Update: Magnitude 7.1 Earthquake in Southern California

Release Date:

Updated on July 12. Visit the USGS earthquake event page for more information.

Scientists from the USGS and other organizations continue field work and analyses to learn more about the series of earthquakes and aftershocks centered in the Southern California desert near Ridgecrest. 

Map showing seismic and GPS deployments as of July 11, 2019

Seismic instruments and GPS deployments as of July 11, 2019. Seismic stations are indicated by triangles and GPS stations are shown as squares. Preliminary mapping of surface ruptures from the July 4 magnitude 6.4 event is shown in black. Ruptures from the July 5 magnitude 7.1 event appear in red.(Credit: USGS. Public domain.)

This includes conducting aerial and ground reconnaissance of the extensive surface rupture, deploying temporary seismic and geodetic stations to record aftershocks, and coordinating efforts with military, state, local and academic partners.

The data collected and knowledge gained will help scientists identify which faults broke during the earthquake, determine the extent of faulting and surface displacement, and locate areas of ground failure to better understand the earthquake and its aftershocks. Some of this information helps us refine the USGS National Seismic Hazards Model, a series of maps that reflect what we know about where shaking is likely to occur over decades — information that is used to develop building codes and design structures to withstand the expected shaking.

 

Instrument Deployments

As of July 11, scientists from USGS, UC Riverside, and the Scripps Institution of Oceanography have deployed temporary equipment including at least 14 seismic and 13 GPS stations as well as five USGS nodal arrays. Additional monitoring equipment will continue to be deployed to learn about this large earthquake.  

These locally installed instruments provide more precise measurements of small aftershocks, ground shaking, and ground deformation than more remote regional instruments can.

 

Map showing general surface ruptures July 4 M6.4 in black and blue; July 5 M7.1 are red.

General surface rupture based on field mapping and satellite data as of July 11, 2019. Ruptures from the magnitude 6.4 event are shown in black and blue, and ruptures from the magnitude 7.1 event are shown in red and green. Circles indicate where scientists have visited the fault surface rupture. (Credit: USGS. Public domain.)

Measuring Surface Ruptures and Fault Offsets

 

The earthquakes were large enough that the fault rupture reached the earth’s surface. Field teams in the Ridgecrest area and on the Naval Air Weapons Station China Lake are documenting fault offsets through direct measurements using tools ranging from tape measures to mobile laser scanning. Their observations show that the magnitude 7.1 event caused a maximum of 6 to10 feet of right-lateral offset along about 30 miles of rupture. Rarely is the surface rupture for large earthquakes expressed as a single, clear break, and in this case the rupture along part of its length is unusually broadly distributed. 

lidar truck

USGS Earthquake Science Center Mobile Laser Scanning truck operated by Ben Brooks and Todd Ericksen scanning the surface rupture near the zone of maximum surface displacement of the M7.1 Searles Valley earthquake. (Credit: Ben Brooks, USGS. Public domain.)

 

Aftershocks and Foreshocks What Has Happened 

 

The aftershock sequence remains very active since the magnitude 7.1 mainshock occurred on July 5. As of July 12, more than 8,900 aftershocks have been recorded including: 

  • more than 540 magnitude 3 or larger events, 
  • 51 magnitude 4 or larger, and 
  • 5 magnitude 5. 
Video animation of Ridgecrest earthquakes before July 4 M6.4 event to noon July 8

This video shows earthquakes from a few hours before the July 4 magnitude 6.4 event through noon on July 8, 2019. The blue dots are the events associated with the magnitude 6.4 and the red dots are associated with the magnitude 7.1 (USGS animation; background image copyright Google Earth Used with Permission)

On July 12 at 6:11 a.m. Pacific Time a moderate magnitude 4.9 aftershock occurred near Ridgecrest.  Aftershocks like this are normal, and in the coming days, seismologists expect additional magnitude 4 or larger aftershocks. So far, all of the magnitude 4 and above aftershocks are occurring within the original aftershock zone. 

 

Aftershock Forecast

 

The odds of a subsequent large earthquake continue to drop. During the week starting July 11, the USGS forecasts a 1 in 200 chance of a magnitude 7 or larger aftershock and a 43% chance of a potentially damaging magnitude 5 or larger aftershock. The chance of aftershocks strong enough to feel near the epicenter —  magnitude 3 or greater —  is virtually certain at more than 99%. Between 39 to 73 such events are expected in the next week.   

See the aftershock forecast for details. This forecast will be updated as conditions change. 

Diagram showing magnitude vs. time for M6.4 and 7.1 earthquakes-aftershocks

The magnitude 6.4 and 7.1 earthquakes and their aftershocks. Aftershock rates for the magnitude7.1 event continue to fall as time passes. Large aftershocks are still possible. (Credit: USGS. Public domain.)

Relation to Coso Geothermal Field and Other Major Faults     

Map showing regional faults and Coso field near Ridgecrest

Map showing the Coso Geothermal Field to the north. The northeast-striking Garlock fault (orange) runs south of Ridgecrest through the center of the map. The San Andreas fault (red) appears in the southwest corner of the map. Faults identified with green, brown or black lines are thought to be less active than those shown in orange and red.  Fault mapping is from the USGS Quaternary Fault and Fold Database. (Credit: USGS. Public domain.)

 

Aftershocks are occurring over about a 37-mile length, with a cluster of activity about 15 miles northwest of the mainshock – with five aftershocks greater than magnitude 4 on July 9 and 10. Interestingly, stopping southeast of the Coso geothermal field.  The Coso field itself is having very little aftershock activity. The scientific field teams are closely monitoring the Coso field and have found no evidence of magmatic activity and no changes in steam production.

Aftershocks at the southern end of the rupture extend to the Garlock fault. Some small earthquakes are occurring on or very close to the Garlock fault. The fault zones that caused the recent earthquakes are complex, and whether they might affect the Garlock, San Andreas, or other regional fault systems is uncertain. The USGS is closely monitoring this situation using instruments installed where these fault systems meet.

 

ShakeMap -- Measuring Earthquake Effects 

 

The California Integrated Seismic Network, a network of about 400 high-quality ground motion sensors, enabled the USGS to produce a map of regional ground shaking shortly after the magnitude 7.1 event. Maximum shaking was estimated at MMI IX (violent) near the epicenter and shaking was very strong (MMI VII) over a broader, approximately 25-mile wide region, including the city of Ridgecrest (see map below).  

A newer version called the Global ShakeMap also incorporates public observations reported into Did You Feel It? to produce a regional map in a little more than 3 hours after the origin time. 

Map showing shaking intensity varied from mild to violent.

The ShakeMap for the magnitude 7.1 event shows shaking in the region varied from mild to violent. (Credit: USGS . Public domain.)

 

 

 

 

 

 

The following content was edited for brevity on July 10, 2019

Updated on July 9, 2019

Aftershock Forecast

According to the current forecast, during the week beginning on July 8, 2019, there is less than a 1 % chance of one or more aftershocks that are larger than magnitude 7.1, and an 8 % chance of a magnitude 6 or larger aftershock. Smaller earthquakes are likely during the next week, with 55 to 120 magnitude 3 or greater aftershocks. Magnitude 3 and above earthquakes are large enough to feel near the epicenter.

Updated on July 8, 2019

The July 5, 2019 magnitude 7.1 earthquake near eastern California’s Searles Valley resulted from shallow strike-slip faulting in the North America plate crust. The magnitude 7.1 event occurred about 34 hours after and about 7 miles northwest of a magnitude 6.4 foreshock on July 4, 2019 at 10:34 a.m. Pacific Time.

The USGS has received more than 40,000 “Did You Feel It?” reports.

During the last three days, scientists with the USGS and California Geological Survey -- with help from the U.S. Navy -- began to survey and map the surface ruptures and offset features that resulted from the earthquake. Results from these investigations will be made public in the coming weeks.

Updated on July 6, 2019

USGS scientists and crews continue to work around the clock on field work, mapping impacted areas and monitoring additional aftershocks to keep the public informed.

The USGS has a revised the alert for economic losses to yellow, meaning that damage is possible, and the impact should be relatively localized. USGS estimates that economic losses will exceed $10 million dollars, with a 30 % chance that losses exceed $100 million dollars. Past events with this alert level have required a local or regional level response. 

The alert remains at green for shaking-related fatalities.

Image shows a map of the earthquake area with quakes marked

Mainshock and aftershock locations shortly after the magnitude 7.1 event, exhibiting a distinctive “T” pattern created by two perpendicular fault zones. The magnitude 6.4 event ruptured along the NE-SW trending fault, and the subsequent magnitude 7.1 event ruptured along the NW-SE trending fault (USGS Public domain).

Aftershock Forecast

According to the current forecast, during the week beginning on July 6, 2019, there is a 2 % chance of one or more aftershocks that are larger than magnitude 7.1. Smaller earthquakes are likely during the next week, with 220 to 330 magnitude 3 or larger aftershocks. Magnitude 3 and above earthquakes are large enough to feel near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.

No one can predict the exact time or place of any earthquake, including aftershocks. The USGS earthquake forecasts help to understand the chances of having more earthquakes within a given time period in the affected area. The USGS calculates this earthquake forecast using a statistical analysis based on past earthquakes.

The forecast changes as time passes due to decline in the frequency of aftershocks, larger aftershocks that may trigger further earthquakes, and changes in forecast modeling based on the data collected for this earthquake sequence.

Image shows a map of the earthquake area with seismic stations overlaid

Map showing the initial alert location (red “+” on green symbol), the four stations that reported the initial alert (green circles), and the USGS network location (yellow circle). Red circle is the S-shaking front at alert time. White circles are approximate S-shaking times at 15 second intervals away from the ANSS epicenter. Blue triangles are seismic stations (USGS Public domain).

ShakeAlert Update

For the magnitude 7.1 earthquake, the ShakeAlert system issued an alert 8.00 seconds after the origin time. The first alert issued estimated the magnitude at 5.5. Within 14 seconds, the system increased its estimated magnitude to 6.3. The USGS is investigating why ShakeAlert underestimated the final magnitude by 0.8 units.

The ShakeAlert system initially estimated the location at 1.6 miles from the ANSS final location, and this measurement did not change significantly. Four stations initially detected the earthquake, with 226 stations contributing to the final alert 40 seconds after detection.

The ShakeAlertLA app was not activated because, as with the earlier magnitude 6.4 earthquake, ShakeAlert estimated no damage in Los Angeles County, the area covered by the app. ShakeAlertLA is currently configured to send alerts for earthquakes of magnitude 5.0 or greater if potential damage from shaking is expected (MMI IV+) in Los Angeles County.

ShakeAlertLA is the nation’s first test of delivering USGS-generated ShakeAlerts to a large population using a city-developed cell phone app. The USGS generates the alerts, but delivery will come by other public and private means -- such as the internet, radio, television, and cellular service -- including the City of Los Angeles ShakeAlertLA app. The City of Los Angeles has been a significant USGS partner in developing the ShakeAlert System in southern California.

Image shows a road with cracks from an earthquake at night

California State Route 178 southwest of Trona, following the magnitude 7.1 earthquake. This road is now closed for repairs. (Credit: Ben Brooks, USGS. Public domain.)

Field Work

Scientists from the USGS and other organizations are on the ground and working to learn more about surface ruptures. The assessment includes canvassing the impacted area for fault displacements, including offsets in roads or curbs, distortion of pipelines, and damage to structures. 

This research will help scientists understand the earthquakes, which faults broke during the earthquake, and the extent of faulting and surface displacement. 

“We have few big earthquakes and we learn something from each one,” said Keith Knudsen, USGS Earthquake Science Center deputy director. “Events like these are an important opportunity to document what happens and could potentially happen in the future.”

The field mapping and seismological work will continue from weeks to months as scientists analyze the collected data. 

Posted July 6, 2019

A magnitude 7.1 earthquake struck southern California on July 5, 2019 at 8:20 p.m. local time (July 6 at 03:20 UTC). This event was centered near the July 4, 2019 magnitude 6.4 earthquake.

The USGS has issued a red alert for economic losses meaning that extensive damage is probable, and the disaster is likely widespread. Estimated economic losses are at least $1 billion dollars, less than 1 % of GDP of the United States. Past events with this alert level have required a national or international level response.

Map of epicenter and past earthquakes in the southern California region

Map shows past earthquakes and the epicenter of the magnitude 7.1 July 5, 2019 southern California earthquake (USGS Public domain).

There is a green alert for shaking-related fatalities with a low likelihood of casualties. The closest large population center is Ridgecrest, population 28,000. Strong to very strong shaking and damage has been reported there.

Shaking from the earthquake was felt by millions of people across the region, including the greater Los Angeles and Las Vegas areas. Visit the USGS event page for more information.

If you felt this earthquake, report your experience on the “USGS Did You Feel It?” website for this event.

The USGS operates a 24/7 National Earthquake Information Center in Colorado that can be reached for more information at 303-273-8500.

Learn more about the USGS Earthquake Hazards Program.