2019 Ridgecrest earthquakes: Difference between revisions

Coordinates: 35°45′58″N 117°36′18″W / 35.766°N 117.605°W / 35.766; -117.605
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At 8:19 p.m. PDT on July 5, a larger, 7.1 {{M|w}} earthquake occurred in the Ridgecrest area, revealing the 6.4 {{M|w}} earthquake to have been a foreshock. Both earthquakes have been described by the United States Geological Survey as occurring via shallow strike-slip mechanisms. Subsequent seismic activity occurred along two intersecting faults in the Airport Lake Fault Zone.<ref>{{short-anss|Ridgecrest|2019c|access-date = July 6, 2019}}.</ref>
At 8:19 p.m. PDT on July 5, a larger, 7.1 {{M|w}} earthquake occurred in the Ridgecrest area, revealing the 6.4 {{M|w}} earthquake to have been a foreshock. Both earthquakes have been described by the United States Geological Survey as occurring via shallow strike-slip mechanisms. Subsequent seismic activity occurred along two intersecting faults in the Airport Lake Fault Zone.<ref>{{short-anss|Ridgecrest|2019c|access-date = July 6, 2019}}.</ref>


Successful [[Earthquake warning system|earthquake early warnings]] were issued by the [[ShakeAlert|USGS ShakeAlert]] system. The average user warning for both earthquakes was 45 seconds. However, the alerts were restricted to areas for which the expected shaking was of intensity V or greater, which did not include Los Angeles. Following complaints about the lack of alerts, the threshold for sending alerts is likely to be lowered in future.<ref name=la_curbed>{{cite web|url=https://la.curbed.com/2019/7/4/20682446/earthquake-los-angeles-fourth-of-july-shake-alert|title = Two large earthquakes rattle LA—but where was the early warning?|date=July 9, 2019|access-date = July 16, 2019}}</ref>
Successful [[Earthquake warning system|earthquake early warnings]] were issued by the [[ShakeAlert|USGS ShakeAlert]] system. [https://earlywarninglabs.com/ Early Warning Labs] became the first and only commercially licenced [[USGS]] partner to successfully deliver [https://www.shakealert.org/ ShakeAlerts] to people & automated systems across Southern California. <ref>https://www.prweb.com/releases/early_warning_labs_delivers_the_only_commercially_licensed_shakealerts_to_people_automated_systems_across_southern_california_during_recent_m6_4_m7_1_earthquakes/prweb16424662.htm</ref> [https://earlywarninglabs.com/ Early Warning Labs] consumer app QuakeAlert, was the only app to successfully deliver mobile alerts. The average user warning for both earthquakes was 45 seconds. <ref>https://la.curbed.com/2019/7/4/20682446/earthquake-los-angeles-fourth-of-july-shake-alert</ref>


===Aftershocks===
===Aftershocks===

Revision as of 18:24, 16 July 2019

35°45′58″N 117°36′18″W / 35.766°N 117.605°W / 35.766; -117.605

2019 Ridgecrest earthquakes
2019 Ridgecrest earthquakes is located in California
Ridgecrest
Ridgecrest
Los Angeles
Los Angeles
Bakersfield
Bakersfield
Las Vegas
Las Vegas
Sacramento
Sacramento
San Diego
San Diego
Tijuana
Tijuana
2019 Ridgecrest earthquakes
UTC time 
 A: 2019-07-04 17:33:49
 B: 2019-07-05 11:07:53
 C: 2019-07-06 03:19:52
ISC eventn/a
USGS-ANSS 
 A: ComCat
 B: ComCat
 C: ComCat
Local date 
 A: July 4, 2019 (2019-07-04)
 B: July 5, 2019 (2019-07-05)
 C: July 5, 2019 (2019-07-05)
Local time 
 A: 10:33 a.m. PDT
 B: 4:08 a.m. PDT
 C: 8:19 p.m. PDT
Magnitude 
 A: Mw6.4[1]
 B: Mw 5.4[2]
 C: Mw 7.1[3]
Depth 
 A: 10.7 km (6.6 mi)
 B: 7.0 km (4.3 mi)
 C: 8.0 km (5.0 mi)
Epicenter35°45′58″N 117°36′18″W / 35.766°N 117.605°W / 35.766; -117.605
TypeStrike-slip
Areas affectedCalifornia, Nevada, Arizona, Baja California
Total damageAt least $100 million
Max. intensityIX (Violent)
Foreshocks2 (≥2.5 Mw )
(including before main foreshock)
Aftershocks4,000
~1,200 (≥2.5 Mw )
(including after main foreshock)
Casualties1 death, 25 injured (20 on July 4, 5 on July 5)

The 2019 Ridgecrest earthquakes of July 4th and 5th occurred north and northeast of the town of Ridgecrest, California (approximately 200 km [122 miles] north-northeast of Los Angeles). They included three main shocks of Mw magnitudes 6.4, 5.4, and 7.1,[4] and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. The first main shock (now deemed to be a foreshock) occurred on July 4 at 10:33 a.m. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona,[5] on a NE-SW trending fault where it intersects the NW-SE trending Airport Lake Fault Zone.[6] This quake was preceded by several smaller earthquakes, and was followed by more than 1,400 detected aftershocks. The M 5.4 and M 7.1 quakes struck on July 5 at 4:08 a.m. and 8:19 p.m. PDT approximately 10 km (6 miles) to the northwest. The latter, now considered the mainshock, was the most powerful earthquake to occur in the state in 20 years.[7] Subsequent aftershocks extended approximately 50 km (~30 miles) along the Airport Lake Fault Zone.

Relatively minor damage resulted from the initial foreshock, though some building fires were reported in Ridgecrest near the epicenter. The main quake on July 5 cut power to at least 3,000 residents in Ridgecrest.[8][7] Effects were felt across much of Southern California, parts of Arizona and Nevada, as far north as the San Francisco Bay Area and Sacramento, and as far south as Baja California, Mexico. An estimated 20 million people experienced the foreshock, and approximately 30 million people experienced the mainshock.[9]

Background

California lies across the mainly transform boundary between the North American and Pacific Plates. About 75% of the displacement between the two plates is taken up by the San Andreas Fault system, with the remaining 25% being accommodated by faults within the Walker Lane/East California Shear Zone.[10]

Although California frequently experiences earthquakes, the state has been in an "earthquake drought" for decades.[11] Prior to the 2019 earthquakes, the last 6 MW or stronger event was the 2014 South Napa earthquake.[12][11] The San Andreas, San Jacinto, and Hayward faults in particular have been exceptionally quiet since 1919, with geologists surmising this to be the only 100-year period in the last 1,000 years with no ground-breaking earthquakes.[11] An average of three to four ground-breaking events are expected each century.[13]

The 2019 earthquakes are the largest in Southern California since the 7.1Mw  Hector Mine Earthquake in October 1999, 20 years earlier;[14] however, that event occurred away from the main plate boundary. The lack of major events in the region is increasing the strain along multiple faults, raising the probability of major earthquake events.[11]

Earthquakes

The July 2019 Ridgecrest earthquakes consist of three main shocks of magnitudes 6.4, 5.4, and 7.1, each followed by a flurry of aftershocks of substantially lower magnitude.

At 10:02 a.m. PDT (17:02 UTC) on July 4, 2019, a 4.0 Mw  foreshock occurred about 6.8 mi (10.9 km) southwest of Searles Valley, California.[15][16] A foreshock registering 6.4 Mw  occurred at 10:33 a.m. PDT (17:33 UTC) 7.5 mi (12.1 km) southwest of Searles Valley.[17] The most populated area near the epicenter was Ridgecrest, home to 28,000 people.[18] The foreshock originated along a strike-slip fault in the Eastern California Shear Zone, a region frequented by earthquake swarms, near the edge of Death Valley National Park.[18][19] The rupture occurred along a 10 mi (16 km) section of an unspecified fault line. Earth on either side of the fault was deformed, with lateral shifts of 6–8 in (15–20 cm) in the immediate vicinity.[20] The exact fault it occurred on is uncertain with many small faults encompassing the region, though United States Geological Survey (USGS) seismologist Susan Hough stated it may have been the Little Lake Fault.[21] Focused at a relatively shallow depth of 6.6 mi (10.7 km), the foreshock affected a large region populated by 20 million people.[17][18] Residents near the epicenter reported that shaking lasted approximately 30 seconds.[21] Shaking was felt as far north as Sacramento, California, eastward to Phoenix, Arizona, and as far south as Baja California, Mexico, with evacuations taking place in Mexicali and Tijuana.[18][22]

At 8:19 p.m. PDT on July 5, a larger, 7.1 Mw  earthquake occurred in the Ridgecrest area, revealing the 6.4 Mw  earthquake to have been a foreshock. Both earthquakes have been described by the United States Geological Survey as occurring via shallow strike-slip mechanisms. Subsequent seismic activity occurred along two intersecting faults in the Airport Lake Fault Zone.[23]

Successful earthquake early warnings were issued by the USGS ShakeAlert system. Early Warning Labs became the first and only commercially licenced USGS partner to successfully deliver ShakeAlerts to people & automated systems across Southern California. [24] Early Warning Labs consumer app QuakeAlert, was the only app to successfully deliver mobile alerts. The average user warning for both earthquakes was 45 seconds. [25]

Aftershocks

The aftershocks of the Ridgecrest earthquakes reveal two fault zones. The July 4th M 6.4 event (orange dot) occurred on the SW-NE fault where it intersects the NW-SE oriented fault. The red dot marks the M 7.1 event.

A significant series of additional earthquakes followed the foreshock, with the majority of magnitudes ranging approximately 2–4 Mw .[26] By the evening of July 5, more than 1,400 earthquakes occurred,[27] the strongest of which measured 5.4 Mw  at 4:07 a.m. PDT (11:07 UTC) on July 5.[28] Shaking from this aftershock was felt as far north as Fresno, as far south as Laguna Hills (including Los Angeles), and as far east as Las Vegas, Nevada. No additional damage occurred from any of the aftershocks.[20] The number of aftershocks within hours of the earthquake is unusually high, but not unprecedented.[29]

Thousands more aftershocks occurred following the 7.1 Mw  event, with the total number of aftershocks exceeding 3,000 by the morning of July 7.[30] Geologists at the USGS estimate an additional 34,000 aftershocks in the six months following the earthquakes.[31]

Events at or above Mw  4.5 associated with the 2019 Ridgecrest earthquakes
Date Time (UTC) Magnitude Mw  Intensity Depth Location Ref.
July 4 17:33:49 6.4 VIII 6.4 mi (10.3 km) 7.5 mi (12 km) SW of Searles Valley [17]
July 4 18:39:44 4.6 VI 1.7 mi (2.8 km) 4.3 mi (7 km) ESE of Ridgecrest [32]
July 4 18:56:06 4.6 VI 1.2 mi (1.9 km) 9.3 mi (15 km) NE of Ridgecrest [33]
July 4 19:21:32 4.5 VI 3.2 mi (5.2 km) 8.1 mi (13 km) SSW of Searles Valley [34]
July 5 11:07:53 5.4 VII 4.3 mi (7.0 km) 9.9 mi (16 km) W of Searles Valley [35]
July 6 03:16:32 5.0 VII 0.56 mi (0.9 km) 8.7 mi (14 km) WSW of Searles Valley [36]
July 6 03:19:53 7.1 IX 5.0 mi (8.0 km) 11 mi (18 km) W of Searles Valley [37]
July 6 03:22:03 4.6 VII 5.7 mi (9.1 km) 9.9 mi (16 km) E of Little Lake [38]
July 6 03:22:48 5.0 VI 5.9 mi (9.5 km) 9.9 mi (16 km) ESE of Little Lake [39]
July 6 03:23:50 5.4 VII 7.7 mi (12.4 km) 11 mi (18 km) WNW of Searles Valley [40]
July 6 03:25:27 5.0 VI 7.0 mi (11.2 km) 14 mi (23 km) ESE of Little Lake [41]
July 6 03:27:06 4.7 VI 8.1 mi (13.0 km) 11 mi (18 km) E of Little Lake [42]
July 6 03:29:29 4.5 VI 6.9 mi (11.1 km) 7.5 mi (12 km) SW of Searles Valley [43]
July 6 03:47:53 5.5 V 2.1 mi (3.4 km) 9.3 mi (15 km) ESE of Little Lake [44]
July 6 03:50:59 4.9 V 4.1 mi (6.6 km) 12 mi (19 km) ESE of Little Lake [45]
July 6 04:13:07 4.8 VI 4.9 mi (7.9 km) 3.7 mi (6 km) SE of Ridgecrest [46]
July 6 04:18:55 5.4 VII 4.6 mi (7.4 km) 12 mi (20 km) E of Little Lake [47]
July 6 04:36:55 4.9 VII 1.2 mi (1.9 km) 9.9 mi (16 km) ESE of Little Lake [48]
July 6 06:01:51 4.6 VI 3.2 mi (5.1 km) 9.3 mi (15 km) E of Little Lake [49]
July 6 08:32:57 4.6 VI 1.9 mi (3.1 km) 9.9 mi (16 km) SSW of Searles Valley [50]
July 6 09:28:28 4.9 VII 2.5 mi (4.0 km) 11 mi (17 km) ESE of Little Lake [51]
July 6 13:06:55 4.5 VI 1.5 mi (2.4 km) 11 mi (18 km) E of Little Lake [52]
July 6 23:50:41 4.5 VII 1.9 mi (3.0 km) 14 mi (22 km) N of Ridgecrest [53]
July 7 05:38:15 4.5 VI 6.6 mi (10.6 km) 9.9 mi (16 km) W of Searles Valley [54]
July 11 00:14:37 4.5 VI 0.50 mi (0.8 km) 9.9 mi (16 km) NNE of Coso Junction [55]
July 12 13:11:37 4.9 VI 6.2 mi (9.9 km) 5.0 mi (8 km) ENE of Ridgecrest [56]

Impact

July 4 foreshock

ShakeMap for M7.1 earthquake
Surface rupture associated with the July 4 earthquake.

Structural damage and two building fires—one of which destroyed half of a home—occurred in Ridgecrest.[18][57] One mobile home was knocked off its foundation and deemed uninhabitable.[20] Around 20 injuries were reported, primarily from shattered glass and falling debris.[58][57] Some gas lines broke, prompting utility companies to shut off service. Businesses experienced product loss, with goods falling off shelves.[59] Emergency personnel responded to nearly two dozen incidents in the city and opened two shelters.[18] Fifteen patients at Ridgecrest Regional Hospital and residents in several apartment buildings were evacuated.[60] Approximately 6,900 customers lost power near the epicenter: 6,000 in Ridgecrest and 900 in Searles Valley.[61] A 4 in (10 cm) wide crack occurred along State Route 178 near Searles Valley and debris covered part of U.S. Route 395.[62][57] In Trona, several buildings sustained damage, water and gas lines broke, and power lines fell. Rockslides covered multiple roads around the community, blocking off mountain roads, including the section of State Route 178 that connects Bakersfield with Lake Isabella.[29] In Los Angeles proper, power outages affected the Fashion District and Granada Hills.[63]

One person died in Pahrump, Nevada, when a lifted jeep he was working under collapsed.[64]

July 5 mainshock

Several fires broke out and five injuries were reported after the mainshock hit, most of them in Ridgecrest and Trona.[65][66] 3,000 people were left without power in Ridgecrest and the rest of Kern County. In Trona, severe damage was reported, with houses knocked off their foundations and numerous gas leaks.[8] Roughly 50 homes were damaged in the town.[67] Multiple rockslides also occurred, making all roads to the city impassable. Water was also in high demand.[8][68] CalTrans once again closed State Route 178 after new cracks and rockslides had occurred.[69]

Overall damage is estimated in excess of $100 million.[64]

Aftermath

July 4 foreshock

Hours after the Mw  6.4 foreshock, California Governor Gavin Newsom approved an emergency proclamation for Kern County.[70][71] Local emergency responders such as the Los Angeles Police Department used social media to alert the public that they were aware of the earthquake and to only use 9-1-1 if there was dangerous conditions or injuries.[72] Routine protocol inspections of major infrastructure, including the Los Angeles Aqueduct, were conducted across the Los Angeles metropolitan area.[12] The Ventura County Fire Department dispatched personnel to survey the county for damage.[62] Naval Air Weapons Station China Lake brought in additional personnel to conduct damage assessments.[57] The USGS sent geologists to Kern County soon after the foreshock to look for a surface rupture and collect data.[12] Disneyland suspended ride operations for inspection.[73]

On July 4, seismologist Dr. Lucy Jones said there is a "1 in 20 chance" that the foreshock would have been followed by larger earthquakes over the next few days. Jones also noted that the magnitude of aftershocks was also likely to increase, with some possibly exceeding 5 Mw .[12]

USGS's ShakeAlert issued a warning 6.9 seconds after the foreshock, about 50 seconds before the foreshock was felt at the Caltech Seismological Laboratory.[74] However, the phone app ShakeAlertLA, which is used to alert residents of Southern California of impending earthquakes, did not activate. This occurred due to the earthquake having a predicted magnitude of 4.5 Mw  in the Los Angeles County area, which is below the activation threshold of 5.0 Mw  and below level 4 on the Modified Mercalli intensity scale ("light shaking"). Due to this, residents were not informed of the earthquake despite the advance notice given to seismologists.[63][75] According to the City of Los Angeles's Twitter account, the threshold will be lowered after this event.[76][77]

July 5 mainshock

Aerial view of a 3–5 ft (0.91–1.52 m) lateral offset on a service road within Naval Air Weapons Station China Lake

The State Operations Center for the California Governor's Office of Emergency Services (Cal OES) was raised to its highest level by Governor Newsom to coordinate resources.[8] The agency distributed cots, water, and food. With temperatures exceeding 100 °F (38 °C), Cal OES established cooling stations in the affected areas.[67] Newsom proclaimed a state of emergency for San Bernardino County on July 6.[78] The California National Guard deployed 200 personnel to assist in relief operations. Power and water service was restored to Ridgecrest and roads were deemed safe by July 7; however, residents were advised to boil water for several days.[67]

Following the shock, (NAWS) Naval Air Weapons Station China Lake evacuated all non essential personnel and declared the base as "not mission capable until further notice" in a statement published on the base's Facebook page on July 6.[79]

In addition, Dr. Lucy Jones said that the odds of another 7 Mw  or above earthquake was a "1 in 10 chance", with a "50-50" chance of a 6 Mw  hitting the Owens Valley. The NW-SE fault is believed to now have increased to between 25 to 30 miles in length.[80]

See also

References

  1. ^ ANSS: Ridgecrest 2019a ..
  2. ^ ANSS: Ridgecrest 2019b ..
  3. ^ ANSS: Ridgecrest 2019c ..
  4. ^ ANSS. "Ridgecrest 2019a: M 6.4 - 12km SW of Searles Valley, CA". Comprehensive Catalog. U.S. Geological Survey. ; ANSS. "Ridgecrest 2019b: M 5.4 - 16km W of Searles Valley, CA". Comprehensive Catalog. U.S. Geological Survey. ; ANSS. "Ridgecrest 2019c: M 7.1 - 18km W of Searles Valley, CA". Comprehensive Catalog. U.S. Geological Survey. .
  5. ^ ANSS: Ridgecrest 2019a, Regional Information ..
  6. ^ ANSS: Ridgecrest 2019c ., "Tectonic Summary".
  7. ^ a b "7.1-Magnitude Earthquake Hits Southern California; Experts Say More Strong Aftershocks Possible". The Weather Company. July 6, 2019. Retrieved July 6, 2019.
  8. ^ a b c d Kaplan, Alejandra Reyes-Velarde, Rosanna Xia, Ruben Vives, Karen. "Second, stronger quake in Ridgecrest shakes Southern California, causing more damage". latimes.com.{{cite web}}: CS1 maint: multiple names: authors list (link)
  9. ^ Doborah Byrd (July 6, 2019). "California shakes from 2nd big quake in 2 days". EarthSky. Retrieved July 7, 2019.
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  24. ^ https://www.prweb.com/releases/early_warning_labs_delivers_the_only_commercially_licensed_shakealerts_to_people_automated_systems_across_southern_california_during_recent_m6_4_m7_1_earthquakes/prweb16424662.htm
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  62. ^ a b Joseph Hong and Ricardo Lopez (July 4, 2019). "6.4 magnitude earthquake rattles Southern California; felt in Coachella Valley". Palm Springs Desert Sun. Retrieved July 4, 2019.
  63. ^ a b "6.4M Quake Strikes Near Ridgecrest In Kern County; No Reports Of Damage In LA". CBSLA. July 4, 2019. Retrieved July 4, 2019.
  64. ^ a b Erika Martin and Eric Spillman (July 10, 2019). "1st Fatality in Ridgecrest Earthquake May Be Man Found Dead Under Jeep 100 Miles From Epicenter: Investigators". KTLA. Retrieved July 10, 2019.
  65. ^ McBride, Jessica (July 6, 2019). "Trona, California Suffers Earthquake Damage, Rockslides". Heavy.com. Retrieved July 6, 2019.
  66. ^ CNN, Christina Maxouris, Sarah Moon and Sheena Jones. "Fires break out after a second and stronger earthquake hits Southern California". CNN. {{cite web}}: |last= has generic name (help)CS1 maint: multiple names: authors list (link)
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External links

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