M6.0 South Napa, California Earthquake – August 24, 2014 | U.S. Geological Survey

M6.0 South Napa, California Earthquake – August 24, 2014 | U.S. Geological Survey
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M6.0 South Napa, California Earthquake – August 24, 2014
Completed
By
Earthquake Hazards Program
August 21, 2024
Overview
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The M6.0 South Napa, California Earthquake was the largest earthquake to strike the San Francisco Bay Area in over 25 years. It caused significant damage to over 100 structures and was widely felt across the region.
Earthquake Probabilities
Earthquake Probabilities in the San Francisco Bay Area by Fault.
View Map
Did You Feel It?
If you felt the Napa earthquake, please tell us about your experience.
Tell Us
What We Have Learned
Media
Sources/Usage: Public Domain.
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Mapped faults and seismicity (magnitude 3+, 1947-2007) prior to the August 24, 2014 South Napa earthquake. The 2000 M4.9 earthquake near Yountville is shown as a white star, and the South Napa earthquake is shown as a yellow star. (Public domain.)
In the wee hours of Sunday morning at 3:20am, on August 24, 2014, the residents and wineries of Napa Valley were shaken by a magnitude 6.0 earthquake, the largest in the San Francisco Bay Area in over 25 years, and the first since the
M7.9 1906 earthquake
to rupture on the surface. Residents in this area feel small earthquakes often, and they generally pause for a moment and then go back to whatever they were doing. But this was no small earthquake, and as the small representative sample of
Jawbone© data
shows, many residents had trouble going back to sleep after this one.
In the days, weeks and months that followed, scientists collected and analyzed data from instruments that recorded the event. Many others spread out across the Napa Valley and surrounding area to collect additional data such as fault rupture expressed on the ground surface, as well as shaking-induced damage to buildings and infrastructure. Data collected from
airborne LIDAR
were used to look for effects on the ground surface. In addition, airborne and ground-based LIDAR data were collected in areas known to have surface cracks to measure and describe what happened.
Tectonic Setting
Media
Sources/Usage: Public Domain.
View Media Details
Seismicity in the Napa area 1973-2015, all magnitudes. (Public domain.)
To put the South Napa earthquake in context, the West Napa fault, which was the causative fault, is part of the large San Andreas Fault Zone (SAFZ) system. The West Napa fault extends along the western margin of the basin that underlies much of Napa Valley. The relative motion on this fault is not well known but is thought to be about 1 mm/yr (0.04 in/yr). The SAFZ is a complex collection of smaller fault segments that collectively accommodate the horizontal movement between the North American Plate and the Pacific Plate.
Sometimes a single fault segment will slip and cause an earthquake, and other times many fault segments slip in unison, causing a larger earthquake. The South Napa earthquake included a few small segments that ruptured together to produce the M6 earthquake. The only other noteworthy earthquake in the Napa area in the recent past (since 1973) was the M4.9 Yountville earthquake on September 3, 2000. The epicenter of that quake was 20 km (12 mi) NNW of the South Napa epicenter, and also happened on the West Napa fault system. In addition, a M3.0 foreshock occurred on August 5, 2014, 19 days before the M6.0 mainshock.
Immediate Impact
Media
Sources/Usage: Public Domain.
View Media Details
The Did You Feel It? map with 41,356 responses as of this writing. (Public domain.)
Many California residents have the
Did You Feel It? (DYFI) webpage
bookmarked, so as soon as the shaking stopped, they started reporting their experience of the shaking on DYFI. Within an hour of the earthquake, over 25,000 citizen scientists entered their experience on the website, creating a
map of the distribution of shaking that they felt
. The highest intensities were
MMI VII-VIII
in the city of Napa and extending a littler further north. Shaking intensities of VII-VIII are described as strong to severe, and very likely woke up all but the most heavy of sleepers. Ultimately, more than 40,000 citizens shared their experiences, with the farthest felt report 300 km (186 mi) to the east in Reno, NV. The
computed instrumental intensities
agreed well with those reported by residents.
The shaking damaged some wood-frame houses and caused significant damage to some commercial buildings in downtown Napa, including the 1870 courthouse. Damage to wood-frame houses included broken or cracked chimneys and failure of cripple walls (see Additional Resources below) and short walls in the crawl space between the foundation and the floor. A few homes even shifted off of their foundations, which can be caused by the failure of cripple walls, which drop the floor to the foundation and sometimes allow houses to slide off their foundation.
Some residents reported a difference in the amount of water being discharged from natural springs. The change occurred within an hour of the earthquake, but the discharge amount returned to normal within a few days. This is not an unusual phenomenon in areas with natural springs and geothermal features. The shaking causes the shifting of below-surface features that may temporarily (and sometimes permanently) change the flow from a spring or even stop the flow. When the pressure adjusts and equilibrates with the water table, the flow will often return. For further details, see
Groundwater Effects from Earthquakes
Media
Sources/Usage: Public Domain.
View Media Details
Aftershocks during the first week after the mainshock. Symbol size represents earthquake magnitude, and fill color represents depth. The crosses and letters indicated cross-sections not shown in this image. (Public domain.)
In the month following the M6.0 mainshock, there were 80 aftershocks of magnitude greater than or equal to 1.8. The three largest aftershocks included a M3.9 on August 26, a M3.2 a week after the mainshock on August 31, and then a M4.1 10 months later on May 22, 2015. The number of aftershocks was less than usual for an earthquake of this size, 80 during the first month following the mainshock, compared to 320 following the M6.0 in Parkfield in 2006.
Fieldwork and Data Analysis
Scientists found that some of the fault segments that ruptured on the morning of August 24 had been previously mapped as part of the West Napa fault system, but the rupture also extended northward where no faults had been mapped before. The length of the rupture was about 12.5 km (8 mi), and scientists measured up to 46 cm (18 in) of slip. No other surface features were found, such as evidence of liquefaction or landslides. This lack of ground failure was attributed to the lack of rainfall in the area—a shallower water table would have made the surface material less stable and more prone to ground failure.
Shallow slipping across the fault, known as afterslip, continued after the mainshock and lasted for several months. Afterslip is slow movement on the fault, and it is unclear whether it is associated with, or independent of, the aftershocks. An additional 14+ cm (5.5+ in) of slip was measured during the first 24 hours, and up to 20 cm (8 in) after 48 hours, mainly on southern half of the main fault strand. Afterslip causes additional damage to manmade structures, such as roads, but does not release seismic waves or cause shaking.
Inspection of buildings after the earthquake yielded 100+ red-tagged structures, meaning immediate rehabitation is too dangerous. Engineers and scientists determined that the worst-damaged buildings resulted from a combination of:
the rupture direction along the fault - to the north and updip towards Napa. (see directivity)
the sedimentary basin - soft sediments amplify the shaking.
commercial buildings were pre-1950 masonry and had not been built to current code standards or retrofit.
wood-frame houses that were damaged were older ones that had not been retrofit (see links below for retrofitting information).
Media
Sources/Usage: Public Domain.
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The South Napa earthquake caused this ground surface rupture running through a viineyard near Buhman Road, Napa Valley, California. (Public domain.)
Media
Sources/Usage: Public Domain.
View Media Details
Locations of the traces of tectonic surface faulting produced by the South Napa earthquake overlain on an aerial photograph. The six traces are labeled A-F. The red star is the location of the mainshock. (Public domain.)
Media
Sources/Usage: Public Domain.
View Media Details
Napa Valley area red- and yellow-tagged structures shown as red and yellow squares. Also shown are locations of the mainshock (red dot), aftershocks (other dots), surface ruptures (red lines), locations of permanent (unfilled triangles) and temporary (filled triangles) seismic stations. (Public domain.)
Media
Sources/Usage: Public Domain.
View Media Details
These two photos showing evidence of afterslip were taken where the fault crosses Highway 12 (south side of the highway) at Cuttings Wharf Road. The first offset measurement was taken the day of the earthquake - about 6 cm (2 in) of right-lateral offset. The following day (almost 24 hrs later), the same feature had 11 cm (4 in) of offset. These measurements are probably minimums for the zone since the deformation was probably distributed over an area of several meters wide. (Credit: Tim Dawson, California Geological Survey. Public domain.)
Broader Impacts
The 2014 earthquake spurred earth scientists to further investigate the West Napa fault, which had been little-studied prior to 2014.  Several paleoseismic trenching investigations have been carried out by USGS and CGS scientists.  These studies suggest that earthquakes on this fault are fairly infrequent, although precise timing of past events remains elusive.  The
map of Quaternary active faults
has been updated to include the 2014 surface ruptures, and mapping of the section of fault north of the 2014 ruptures is currently being improved based on LIDAR data and field examination.  Preliminary results suggest that the fault extends along the southwest side of Napa Valley farther north than previously recognized, past the town of Calistoga.  The 2014 earthquake serves as a reminder that the numerous less-active faults throughout the Bay Area in California nevertheless pose significant hazards and are worthy of scientific investigation and public awareness.  While each individual fault may produce earthquakes only once every few thousand years, collectively these less-active faults account for a 13% chance of an earthquake above magnitude 6.7 before 2043,
contributing to an overall 72% chance of such an earthquake from all known faults
Concluding Thoughts
This earthquake was unusual for its size, because it had a relatively long surface rupture of 12.5 km (8 mi) with a significant amount of surface slip (up to 46 cm, or 18 in). It also had a large amount of afterslip, and fewer aftershocks than average for an earthquake of its size. However, knowledge gained provides new insights into the influence of the sedimentary basin under the Napa region, which can be used in future hazard maps to more accurately forecast earthquake hazards in the area.
Additional Resources
USGS Event page - ShakeMap, Did You Feel It? and more details about the Napa Earthquake
Earthquake outlook for the San Francisco Bay region 2014–2043
Protecting Your Family From Earthquakes
(English/Spanish; .pdf)
Protecting Your Family From Earthquakes
(Asian-languages; .pdf)
Earthquake Strengthening of Cripple Walls in Wood-Frame Dwellings
(.pdf)
Quantifying Business Interruption, Downtime, and Recovery following the 2014 South Napa Earthquake and Identifying the Causes
(.pdf)
Additional Publications
Earthquake Country Alliance Bay Area
Scientific Staff
Earthquake Science Center, Moffett Field, California
Geologic Hazards Science Center, Golden, Colorado
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Slide show of multimedia items associated with this project.
September 23, 2021
2014 South Napa
2014 South Napa
2014 South Napa
By
Natural Hazards
Earthquake Hazards
California
September 23, 2021
2014 South Napa
2014 South Napa
2014 South Napa
2014 South Napa
By
Natural Hazards
Earthquake Hazards
California
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
September 11, 2014
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the brick exterior of the downtown Napa Post Office. Photo take September 11, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
September 11, 2014
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the brick exterior of the downtown Napa Post Office. Photo take September 11, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Collecting topographic data
Collecting topographic data
August 26, 2014
Collecting topographic data
Collecting topographic data
Collecting topographic data
USGS summer geology interns Alexandra Pickering and Nikita Avdievitch collecting topographic data with a three-dimensional laser scanner on August 26. Surface rupture from the 2014 South Napa Earthquake is visible in the foreground
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 26, 2014
Collecting topographic data
Collecting topographic data
Collecting topographic data
Collecting topographic data
USGS summer geology interns Alexandra Pickering and Nikita Avdievitch collecting topographic data with a three-dimensional laser scanner on August 26. Surface rupture from the 2014 South Napa Earthquake is visible in the foreground
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
August 24, 2014
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
USGS volunteer Whitney DeLong and geology intern Alexandra Pickering collecting topographic data with a three-dimensional laser scanner along Cuttings Wharf Road in Napa County, CA on August 26, 2014. In the background are engineers inspecting the earthquake surface rupture where is passes through a horse paddock.
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
USGS volunteer Whitney DeLong and geology intern Alexandra Pickering collecting topographic data with a three-dimensional laser scanner along Cuttings Wharf Road in Napa County, CA on August 26, 2014. In the background are engineers inspecting the earthquake surface rupture where is passes through a horse paddock.
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
August 24, 2014
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA caused by the South Napa earthquake. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
August 24, 2014
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA caused by the South Napa earthquake. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Surface rupture
Surface rupture
August 24, 2014
Surface rupture
Surface rupture
Surface rupture
Surface rupture in soil near the intersection of state Highway 12 and Cuttings Wharf Road in Napa, CA on August 24, 2104
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture
Surface rupture
Surface rupture
Surface rupture
Surface rupture in soil near the intersection of state Highway 12 and Cuttings Wharf Road in Napa, CA on August 24, 2104
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
August 24, 2014
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave just northwest of South Ave in Napa County, CA. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave just northwest of South Ave in Napa County, CA. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Surface rupture across State Highway 12
Surface rupture across State Highway 12
August 24, 2014
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12 at Cuttings Wharf Road - Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12 at Cuttings Wharf Road - Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
October 31, 2019
Coseismic slip and early afterslip of the M6.0 August 24, 2014 South Napa, California, earthquake
Coseismic slip and early afterslip of the M6.0 August 24, 2014 South Napa, California, earthquake
We employ strong motion seismograms and static offsets from the Global Positioning System, Interferometric Synthetic Aperture Radar, and other measurements in order to derive a coseismic slip and afterslip model of the M6.0 24 August 2014 South Napa earthquake. This earthquake ruptured an ∼13‐km‐long portion of the West Napa fault with predominantly right‐lateral strike slip. In the...
Authors
Frederick Pollitz, Jessica R. Murray, Sarah E. Minson, Charles W. Wicks, Jerry L. Svarc, Benjamin A. Brooks
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 8, 2019
The Mw 6.0 South Napa earthquake of August 24, 2014—Observations of surface faulting and ground deformation, with recommendations for improving post-earthquake field investigations
The Mw 6.0 South Napa earthquake of August 24, 2014—Observations of surface faulting and ground deformation, with recommendations for improving post-earthquake field investigations
The Mw 6.0 South Napa earthquake of August 24, 2014, produced complex and extensive surface faulting and other ground deformation features. Following the event, geologists made more than 1,200 field observations at locations where tectonic faulting and ground failure produced visible deformation that fractured and disturbed the ground surface. At a few locations, large-scale, detailed...
Authors
Daniel J. Ponti, Carla M. Rosa, James Luke Blair
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
November 1, 2016
Continuity of the West Napa–Franklin fault zone inferred from guided waves generated by earthquakes following the 24 August 2014 Mw 6.0 South Napa Earthquake
Continuity of the West Napa–Franklin fault zone inferred from guided waves generated by earthquakes following the 24 August 2014 Mw 6.0 South Napa Earthquake
We measure peak ground velocities from fault‐zone guided waves (FZGWs), generated by on‐fault earthquakes associated with the 24 August 2014 Mw 6.0 South Napa earthquake. The data were recorded on three arrays deployed across north and south of the 2014 surface rupture. The observed FZGWs indicate that the West Napa fault zone (WNFZ) and the Franklin fault (FF) are continuous in the...
Authors
Rufus D. Catchings, Mark R. Goldman, Y.-G. Li, Joanne H. Chan
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
October 22, 2016
Tearing the terroir: Details and implications of surface rupture and deformation from the 24 August 2014 M6.0 South Napa earthquake, California
Tearing the terroir: Details and implications of surface rupture and deformation from the 24 August 2014 M6.0 South Napa earthquake, California
The Mw 6.0 South Napa earthquake of 24 August 2014 caused slip on several active fault strands within the West Napa Fault Zone (WNFZ). Field mapping identified 12.5 km of surface rupture. These field observations, near-field geodesy and space geodesy, together provide evidence for more than ~30 km of surface deformation with a relatively complex distribution across a number of...
Authors
Stephen B. DeLong, Andrea Donnellan, Daniel J. Ponti, Ron S. Rubin, James J. Lienkaemper, Carol S. Prentice, Timothy E. Dawson, Gordon G. Seitz, David P. Schwartz, Kenneth W. Hudnut, Carla M. Rosa, Alexandra J. Pickering, Jay W. Parker
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
June 22, 2016
Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults
Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults
We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double...
Authors
Jeanne L. Hardebeck, David R. Shelly
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 1, 2016
Afterslip behavior following the M6.0, 2014 South Napa earthquake with implications for afterslip forecasting on other seismogenic faults
Afterslip behavior following the M6.0, 2014 South Napa earthquake with implications for afterslip forecasting on other seismogenic faults
The M6.0, 24 Aug. 2014 South Napa, California, earthquake exhibited unusually large slip for a California strike-slip event of its size with a maximum coseismic surface slip of 40-50 cm in the north section of the 15 km-long rupture. Although only minor (
Authors
James J. Lienkaemper, Stephen B. DeLong, Carolyn J Domrose, Carla M. Rosa
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
December 31, 2015
2014 M=6.0 South Napa earthquake triggered widespread aftershocks and stressed several major faults and exotic fault clusters
2014 M=6.0 South Napa earthquake triggered widespread aftershocks and stressed several major faults and exotic fault clusters
The strongest San Francisco Bay area earthquake since the 1989 Mw 7.0 Loma Prieta shock struck near Napa on 24 August 2014. Field mapping (Dawson et al., 2014; Earthquake Engineering Research Institute [EERI], 2014; Brocher et al., 2015) and seismic and geodetic source inversions (Barnhart et al., 2015; Dreger et al., 2015; Wei et al., 2015) indicate that a 15-km-long northwest-trending...
Authors
Shinji Toda, Ross Stein
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 5, 2015
The Mw6.0 24 August 2014 South Napa earthquake
The Mw6.0 24 August 2014 South Napa earthquake
The Mw 6.0 South Napa earthquake, which occurred at 10:20 UTC 24 August 2014 was the largest earthquake to strike the greater San Francisco Bay area since the Mw 6.9 1989 Loma Prieta earthquake. The rupture from this right‐lateral earthquake propagated mostly unilaterally to the north and up‐dip, directing the strongest shaking toward the city of Napa, where peak ground accelerations...
Authors
Thomas M. Brocher, Annemarie S. Baltay Sundstrom, Jeanne L. Hardebeck, Fred F. Pollitz, Jessica R. Murray, Andrea L. Llenos, David P. Schwartz, J. Luke Blair, Daniel J. Ponti, James J. Lienkaemper, Victoria E. Langenheim, Timothy E. Dawson, Kenneth W. Hudnut, David R. Shelly, Douglas S. Dreger, John Boatwright, Brad T. Aagaard, David J. Wald, Richard M. Allen, William D. Barnhart, Keith L. Knudsen, Benjamin A. Brooks, Katherine M. Scharer
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Below are news stories associated with this project.
Harvesting Earthquake Fault Slip f­rom Laser Images of Napa's Vineyards
July 31, 2017
Harvesting Earthquake Fault Slip f­rom Laser Images of Napa's Vineyards
A new U.S. Geological Survey-led study suggests that earthquake-related deformation just below the Earth's surface can be quite different from how it...
Read Article
Scientists Deploy Seismographs in Napa Valley
August 11, 2016
Scientists Deploy Seismographs in Napa Valley
Media Advisory: Photo Opportunity
Read Article
South Napa Earthquake – One Year Later
August 21, 2015
South Napa Earthquake – One Year Later
One year ago, the largest earthquake in over 25 years hit the San Francisco Bay Area, causing significant damage in California’s famous Napa Valley...
Read Article
Scientists gather at USGS to discuss findings from Napa quake
January 28, 2015
Scientists gather at USGS to discuss findings from Napa quake
MENLO PARK, Calif. (KGO) --
Five months after the South Napa earthquake, scientists gathered on Wednesday at the U.S. Geological Survey to talk about...
Read Article
Media Advisory: South Napa Earthquake Science Briefing
September 3, 2014
Media Advisory: South Napa Earthquake Science Briefing
Members of the news media are invited to attend a scientific briefing at the U.S. Geological Survey to summarize what has been learned about and from...
Read Article
Tuesday Midday Update on South Napa Earthquake
August 26, 2014
Tuesday Midday Update on South Napa Earthquake
This release of information serves as an updated summary of U.S. Geological Survey information as it relates to the current understanding of the South...
Read Article
Update on the Magnitude 6 South Napa Earthquake of August 24, 2014
August 25, 2014
Update on the Magnitude 6 South Napa Earthquake of August 24, 2014
Yesterday at 3:20 AM local time, the northern San Francisco Bay Area was struck by the largest earthquake to impact the Bay Area since the 1989 M6.9...
Read Article
The M6.0 South Napa, California Earthquake was the largest earthquake to strike the San Francisco Bay Area in over 25 years. It caused significant damage to over 100 structures and was widely felt across the region.
Earthquake Probabilities
Earthquake Probabilities in the San Francisco Bay Area by Fault.
View Map
Did You Feel It?
If you felt the Napa earthquake, please tell us about your experience.
Tell Us
What We Have Learned
Media
Sources/Usage: Public Domain.
View Media Details
Mapped faults and seismicity (magnitude 3+, 1947-2007) prior to the August 24, 2014 South Napa earthquake. The 2000 M4.9 earthquake near Yountville is shown as a white star, and the South Napa earthquake is shown as a yellow star. (Public domain.)
In the wee hours of Sunday morning at 3:20am, on August 24, 2014, the residents and wineries of Napa Valley were shaken by a magnitude 6.0 earthquake, the largest in the San Francisco Bay Area in over 25 years, and the first since the
M7.9 1906 earthquake
to rupture on the surface. Residents in this area feel small earthquakes often, and they generally pause for a moment and then go back to whatever they were doing. But this was no small earthquake, and as the small representative sample of
Jawbone© data
shows, many residents had trouble going back to sleep after this one.
In the days, weeks and months that followed, scientists collected and analyzed data from instruments that recorded the event. Many others spread out across the Napa Valley and surrounding area to collect additional data such as fault rupture expressed on the ground surface, as well as shaking-induced damage to buildings and infrastructure. Data collected from
airborne LIDAR
were used to look for effects on the ground surface. In addition, airborne and ground-based LIDAR data were collected in areas known to have surface cracks to measure and describe what happened.
Tectonic Setting
Media
Sources/Usage: Public Domain.
View Media Details
Seismicity in the Napa area 1973-2015, all magnitudes. (Public domain.)
To put the South Napa earthquake in context, the West Napa fault, which was the causative fault, is part of the large San Andreas Fault Zone (SAFZ) system. The West Napa fault extends along the western margin of the basin that underlies much of Napa Valley. The relative motion on this fault is not well known but is thought to be about 1 mm/yr (0.04 in/yr). The SAFZ is a complex collection of smaller fault segments that collectively accommodate the horizontal movement between the North American Plate and the Pacific Plate.
Sometimes a single fault segment will slip and cause an earthquake, and other times many fault segments slip in unison, causing a larger earthquake. The South Napa earthquake included a few small segments that ruptured together to produce the M6 earthquake. The only other noteworthy earthquake in the Napa area in the recent past (since 1973) was the M4.9 Yountville earthquake on September 3, 2000. The epicenter of that quake was 20 km (12 mi) NNW of the South Napa epicenter, and also happened on the West Napa fault system. In addition, a M3.0 foreshock occurred on August 5, 2014, 19 days before the M6.0 mainshock.
Immediate Impact
Media
Sources/Usage: Public Domain.
View Media Details
The Did You Feel It? map with 41,356 responses as of this writing. (Public domain.)
Many California residents have the
Did You Feel It? (DYFI) webpage
bookmarked, so as soon as the shaking stopped, they started reporting their experience of the shaking on DYFI. Within an hour of the earthquake, over 25,000 citizen scientists entered their experience on the website, creating a
map of the distribution of shaking that they felt
. The highest intensities were
MMI VII-VIII
in the city of Napa and extending a littler further north. Shaking intensities of VII-VIII are described as strong to severe, and very likely woke up all but the most heavy of sleepers. Ultimately, more than 40,000 citizens shared their experiences, with the farthest felt report 300 km (186 mi) to the east in Reno, NV. The
computed instrumental intensities
agreed well with those reported by residents.
The shaking damaged some wood-frame houses and caused significant damage to some commercial buildings in downtown Napa, including the 1870 courthouse. Damage to wood-frame houses included broken or cracked chimneys and failure of cripple walls (see Additional Resources below) and short walls in the crawl space between the foundation and the floor. A few homes even shifted off of their foundations, which can be caused by the failure of cripple walls, which drop the floor to the foundation and sometimes allow houses to slide off their foundation.
Some residents reported a difference in the amount of water being discharged from natural springs. The change occurred within an hour of the earthquake, but the discharge amount returned to normal within a few days. This is not an unusual phenomenon in areas with natural springs and geothermal features. The shaking causes the shifting of below-surface features that may temporarily (and sometimes permanently) change the flow from a spring or even stop the flow. When the pressure adjusts and equilibrates with the water table, the flow will often return. For further details, see
Groundwater Effects from Earthquakes
Media
Sources/Usage: Public Domain.
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Aftershocks during the first week after the mainshock. Symbol size represents earthquake magnitude, and fill color represents depth. The crosses and letters indicated cross-sections not shown in this image. (Public domain.)
In the month following the M6.0 mainshock, there were 80 aftershocks of magnitude greater than or equal to 1.8. The three largest aftershocks included a M3.9 on August 26, a M3.2 a week after the mainshock on August 31, and then a M4.1 10 months later on May 22, 2015. The number of aftershocks was less than usual for an earthquake of this size, 80 during the first month following the mainshock, compared to 320 following the M6.0 in Parkfield in 2006.
Fieldwork and Data Analysis
Scientists found that some of the fault segments that ruptured on the morning of August 24 had been previously mapped as part of the West Napa fault system, but the rupture also extended northward where no faults had been mapped before. The length of the rupture was about 12.5 km (8 mi), and scientists measured up to 46 cm (18 in) of slip. No other surface features were found, such as evidence of liquefaction or landslides. This lack of ground failure was attributed to the lack of rainfall in the area—a shallower water table would have made the surface material less stable and more prone to ground failure.
Shallow slipping across the fault, known as afterslip, continued after the mainshock and lasted for several months. Afterslip is slow movement on the fault, and it is unclear whether it is associated with, or independent of, the aftershocks. An additional 14+ cm (5.5+ in) of slip was measured during the first 24 hours, and up to 20 cm (8 in) after 48 hours, mainly on southern half of the main fault strand. Afterslip causes additional damage to manmade structures, such as roads, but does not release seismic waves or cause shaking.
Inspection of buildings after the earthquake yielded 100+ red-tagged structures, meaning immediate rehabitation is too dangerous. Engineers and scientists determined that the worst-damaged buildings resulted from a combination of:
the rupture direction along the fault - to the north and updip towards Napa. (see directivity)
the sedimentary basin - soft sediments amplify the shaking.
commercial buildings were pre-1950 masonry and had not been built to current code standards or retrofit.
wood-frame houses that were damaged were older ones that had not been retrofit (see links below for retrofitting information).
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Sources/Usage: Public Domain.
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The South Napa earthquake caused this ground surface rupture running through a viineyard near Buhman Road, Napa Valley, California. (Public domain.)
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Sources/Usage: Public Domain.
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Locations of the traces of tectonic surface faulting produced by the South Napa earthquake overlain on an aerial photograph. The six traces are labeled A-F. The red star is the location of the mainshock. (Public domain.)
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Sources/Usage: Public Domain.
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Napa Valley area red- and yellow-tagged structures shown as red and yellow squares. Also shown are locations of the mainshock (red dot), aftershocks (other dots), surface ruptures (red lines), locations of permanent (unfilled triangles) and temporary (filled triangles) seismic stations. (Public domain.)
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These two photos showing evidence of afterslip were taken where the fault crosses Highway 12 (south side of the highway) at Cuttings Wharf Road. The first offset measurement was taken the day of the earthquake - about 6 cm (2 in) of right-lateral offset. The following day (almost 24 hrs later), the same feature had 11 cm (4 in) of offset. These measurements are probably minimums for the zone since the deformation was probably distributed over an area of several meters wide. (Credit: Tim Dawson, California Geological Survey. Public domain.)
Broader Impacts
The 2014 earthquake spurred earth scientists to further investigate the West Napa fault, which had been little-studied prior to 2014.  Several paleoseismic trenching investigations have been carried out by USGS and CGS scientists.  These studies suggest that earthquakes on this fault are fairly infrequent, although precise timing of past events remains elusive.  The
map of Quaternary active faults
has been updated to include the 2014 surface ruptures, and mapping of the section of fault north of the 2014 ruptures is currently being improved based on LIDAR data and field examination.  Preliminary results suggest that the fault extends along the southwest side of Napa Valley farther north than previously recognized, past the town of Calistoga.  The 2014 earthquake serves as a reminder that the numerous less-active faults throughout the Bay Area in California nevertheless pose significant hazards and are worthy of scientific investigation and public awareness.  While each individual fault may produce earthquakes only once every few thousand years, collectively these less-active faults account for a 13% chance of an earthquake above magnitude 6.7 before 2043,
contributing to an overall 72% chance of such an earthquake from all known faults
Concluding Thoughts
This earthquake was unusual for its size, because it had a relatively long surface rupture of 12.5 km (8 mi) with a significant amount of surface slip (up to 46 cm, or 18 in). It also had a large amount of afterslip, and fewer aftershocks than average for an earthquake of its size. However, knowledge gained provides new insights into the influence of the sedimentary basin under the Napa region, which can be used in future hazard maps to more accurately forecast earthquake hazards in the area.
Additional Resources
USGS Event page - ShakeMap, Did You Feel It? and more details about the Napa Earthquake
Earthquake outlook for the San Francisco Bay region 2014–2043
Protecting Your Family From Earthquakes
(English/Spanish; .pdf)
Protecting Your Family From Earthquakes
(Asian-languages; .pdf)
Earthquake Strengthening of Cripple Walls in Wood-Frame Dwellings
(.pdf)
Quantifying Business Interruption, Downtime, and Recovery following the 2014 South Napa Earthquake and Identifying the Causes
(.pdf)
Additional Publications
Earthquake Country Alliance Bay Area
Scientific Staff
Earthquake Science Center, Moffett Field, California
Geologic Hazards Science Center, Golden, Colorado
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Slide show of multimedia items associated with this project.
September 23, 2021
2014 South Napa
2014 South Napa
2014 South Napa
By
Natural Hazards
Earthquake Hazards
California
September 23, 2021
2014 South Napa
2014 South Napa
2014 South Napa
2014 South Napa
By
Natural Hazards
Earthquake Hazards
California
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
September 11, 2014
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the brick exterior of the downtown Napa Post Office. Photo take September 11, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
September 11, 2014
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the downtown Napa Post Office
Damage to the brick exterior of the downtown Napa Post Office. Photo take September 11, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Collecting topographic data
Collecting topographic data
August 26, 2014
Collecting topographic data
Collecting topographic data
Collecting topographic data
USGS summer geology interns Alexandra Pickering and Nikita Avdievitch collecting topographic data with a three-dimensional laser scanner on August 26. Surface rupture from the 2014 South Napa Earthquake is visible in the foreground
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 26, 2014
Collecting topographic data
Collecting topographic data
Collecting topographic data
Collecting topographic data
USGS summer geology interns Alexandra Pickering and Nikita Avdievitch collecting topographic data with a three-dimensional laser scanner on August 26. Surface rupture from the 2014 South Napa Earthquake is visible in the foreground
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
August 24, 2014
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
USGS volunteer Whitney DeLong and geology intern Alexandra Pickering collecting topographic data with a three-dimensional laser scanner along Cuttings Wharf Road in Napa County, CA on August 26, 2014. In the background are engineers inspecting the earthquake surface rupture where is passes through a horse paddock.
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
Collecting topographic data with a three-dimensional laser scanner
USGS volunteer Whitney DeLong and geology intern Alexandra Pickering collecting topographic data with a three-dimensional laser scanner along Cuttings Wharf Road in Napa County, CA on August 26, 2014. In the background are engineers inspecting the earthquake surface rupture where is passes through a horse paddock.
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
August 24, 2014
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA caused by the South Napa earthquake. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
August 24, 2014
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA
Damage to a building in downtown Napa, CA caused by the South Napa earthquake. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Surface rupture
Surface rupture
August 24, 2014
Surface rupture
Surface rupture
Surface rupture
Surface rupture in soil near the intersection of state Highway 12 and Cuttings Wharf Road in Napa, CA on August 24, 2104
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture
Surface rupture
Surface rupture
Surface rupture
Surface rupture in soil near the intersection of state Highway 12 and Cuttings Wharf Road in Napa, CA on August 24, 2104
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
August 24, 2014
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave just northwest of South Ave in Napa County, CA. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave
Surface rupture across Los Carneros Ave just northwest of South Ave in Napa County, CA. Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Surface rupture across State Highway 12
Surface rupture across State Highway 12
August 24, 2014
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12 at Cuttings Wharf Road - Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
August 24, 2014
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12
Surface rupture across State Highway 12 at Cuttings Wharf Road - Photo taken by USGS from California Highway Patrol helicopter on August 24, 2014
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
October 31, 2019
Coseismic slip and early afterslip of the M6.0 August 24, 2014 South Napa, California, earthquake
Coseismic slip and early afterslip of the M6.0 August 24, 2014 South Napa, California, earthquake
We employ strong motion seismograms and static offsets from the Global Positioning System, Interferometric Synthetic Aperture Radar, and other measurements in order to derive a coseismic slip and afterslip model of the M6.0 24 August 2014 South Napa earthquake. This earthquake ruptured an ∼13‐km‐long portion of the West Napa fault with predominantly right‐lateral strike slip. In the...
Authors
Frederick Pollitz, Jessica R. Murray, Sarah E. Minson, Charles W. Wicks, Jerry L. Svarc, Benjamin A. Brooks
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 8, 2019
The Mw 6.0 South Napa earthquake of August 24, 2014—Observations of surface faulting and ground deformation, with recommendations for improving post-earthquake field investigations
The Mw 6.0 South Napa earthquake of August 24, 2014—Observations of surface faulting and ground deformation, with recommendations for improving post-earthquake field investigations
The Mw 6.0 South Napa earthquake of August 24, 2014, produced complex and extensive surface faulting and other ground deformation features. Following the event, geologists made more than 1,200 field observations at locations where tectonic faulting and ground failure produced visible deformation that fractured and disturbed the ground surface. At a few locations, large-scale, detailed...
Authors
Daniel J. Ponti, Carla M. Rosa, James Luke Blair
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
November 1, 2016
Continuity of the West Napa–Franklin fault zone inferred from guided waves generated by earthquakes following the 24 August 2014 Mw 6.0 South Napa Earthquake
Continuity of the West Napa–Franklin fault zone inferred from guided waves generated by earthquakes following the 24 August 2014 Mw 6.0 South Napa Earthquake
We measure peak ground velocities from fault‐zone guided waves (FZGWs), generated by on‐fault earthquakes associated with the 24 August 2014 Mw 6.0 South Napa earthquake. The data were recorded on three arrays deployed across north and south of the 2014 surface rupture. The observed FZGWs indicate that the West Napa fault zone (WNFZ) and the Franklin fault (FF) are continuous in the...
Authors
Rufus D. Catchings, Mark R. Goldman, Y.-G. Li, Joanne H. Chan
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
October 22, 2016
Tearing the terroir: Details and implications of surface rupture and deformation from the 24 August 2014 M6.0 South Napa earthquake, California
Tearing the terroir: Details and implications of surface rupture and deformation from the 24 August 2014 M6.0 South Napa earthquake, California
The Mw 6.0 South Napa earthquake of 24 August 2014 caused slip on several active fault strands within the West Napa Fault Zone (WNFZ). Field mapping identified 12.5 km of surface rupture. These field observations, near-field geodesy and space geodesy, together provide evidence for more than ~30 km of surface deformation with a relatively complex distribution across a number of...
Authors
Stephen B. DeLong, Andrea Donnellan, Daniel J. Ponti, Ron S. Rubin, James J. Lienkaemper, Carol S. Prentice, Timothy E. Dawson, Gordon G. Seitz, David P. Schwartz, Kenneth W. Hudnut, Carla M. Rosa, Alexandra J. Pickering, Jay W. Parker
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
June 22, 2016
Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults
Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults
We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double...
Authors
Jeanne L. Hardebeck, David R. Shelly
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 1, 2016
Afterslip behavior following the M6.0, 2014 South Napa earthquake with implications for afterslip forecasting on other seismogenic faults
Afterslip behavior following the M6.0, 2014 South Napa earthquake with implications for afterslip forecasting on other seismogenic faults
The M6.0, 24 Aug. 2014 South Napa, California, earthquake exhibited unusually large slip for a California strike-slip event of its size with a maximum coseismic surface slip of 40-50 cm in the north section of the 15 km-long rupture. Although only minor (
Authors
James J. Lienkaemper, Stephen B. DeLong, Carolyn J Domrose, Carla M. Rosa
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
December 31, 2015
2014 M=6.0 South Napa earthquake triggered widespread aftershocks and stressed several major faults and exotic fault clusters
2014 M=6.0 South Napa earthquake triggered widespread aftershocks and stressed several major faults and exotic fault clusters
The strongest San Francisco Bay area earthquake since the 1989 Mw 7.0 Loma Prieta shock struck near Napa on 24 August 2014. Field mapping (Dawson et al., 2014; Earthquake Engineering Research Institute [EERI], 2014; Brocher et al., 2015) and seismic and geodetic source inversions (Barnhart et al., 2015; Dreger et al., 2015; Wei et al., 2015) indicate that a 15-km-long northwest-trending...
Authors
Shinji Toda, Ross Stein
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
March 5, 2015
The Mw6.0 24 August 2014 South Napa earthquake
The Mw6.0 24 August 2014 South Napa earthquake
The Mw 6.0 South Napa earthquake, which occurred at 10:20 UTC 24 August 2014 was the largest earthquake to strike the greater San Francisco Bay area since the Mw 6.9 1989 Loma Prieta earthquake. The rupture from this right‐lateral earthquake propagated mostly unilaterally to the north and up‐dip, directing the strongest shaking toward the city of Napa, where peak ground accelerations...
Authors
Thomas M. Brocher, Annemarie S. Baltay Sundstrom, Jeanne L. Hardebeck, Fred F. Pollitz, Jessica R. Murray, Andrea L. Llenos, David P. Schwartz, J. Luke Blair, Daniel J. Ponti, James J. Lienkaemper, Victoria E. Langenheim, Timothy E. Dawson, Kenneth W. Hudnut, David R. Shelly, Douglas S. Dreger, John Boatwright, Brad T. Aagaard, David J. Wald, Richard M. Allen, William D. Barnhart, Keith L. Knudsen, Benjamin A. Brooks, Katherine M. Scharer
By
Natural Hazards Mission Area
Earthquake Hazards Program
Earthquake Science Center
Below are news stories associated with this project.
Harvesting Earthquake Fault Slip f­rom Laser Images of Napa's Vineyards
July 31, 2017
Harvesting Earthquake Fault Slip f­rom Laser Images of Napa's Vineyards
A new U.S. Geological Survey-led study suggests that earthquake-related deformation just below the Earth's surface can be quite different from how it...
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Scientists Deploy Seismographs in Napa Valley
August 11, 2016
Scientists Deploy Seismographs in Napa Valley
Media Advisory: Photo Opportunity
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South Napa Earthquake – One Year Later
August 21, 2015
South Napa Earthquake – One Year Later
One year ago, the largest earthquake in over 25 years hit the San Francisco Bay Area, causing significant damage in California’s famous Napa Valley...
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Scientists gather at USGS to discuss findings from Napa quake
January 28, 2015
Scientists gather at USGS to discuss findings from Napa quake
MENLO PARK, Calif. (KGO) --
Five months after the South Napa earthquake, scientists gathered on Wednesday at the U.S. Geological Survey to talk about...
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Media Advisory: South Napa Earthquake Science Briefing
September 3, 2014
Media Advisory: South Napa Earthquake Science Briefing
Members of the news media are invited to attend a scientific briefing at the U.S. Geological Survey to summarize what has been learned about and from...
Read Article
Tuesday Midday Update on South Napa Earthquake
August 26, 2014
Tuesday Midday Update on South Napa Earthquake
This release of information serves as an updated summary of U.S. Geological Survey information as it relates to the current understanding of the South...
Read Article
Update on the Magnitude 6 South Napa Earthquake of August 24, 2014
August 25, 2014
Update on the Magnitude 6 South Napa Earthquake of August 24, 2014
Yesterday at 3:20 AM local time, the northern San Francisco Bay Area was struck by the largest earthquake to impact the Bay Area since the 1989 M6.9...
Read Article
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