2019 Ridgecrest earthquakes

The 2019 Ridgecrest earthquakes (more commonly referred to in scientific literature as the 2019 Ridgecrest earthquake sequence) of July 4 and 5 occurred north and northeast of the town of Ridgecrest, California and west of Searles Valley (approximately 200 km [122 mi] north-northeast of Los Angeles). They included three initial main shocks of Mw magnitudes 6.4, 5.4, and 7.1,[5] and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. Eleven months later, a Mw  5.5 aftershock took place (the largest of the sequence) to the east of Ridgecrest. 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,[6] on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone.[7] 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 (after the 1999 Hector Mine earthquake).[8] Subsequent aftershocks extended approximately 50 km (~30 miles) along the Little Lake Fault Zone.

2019-2020 Ridgecrest earthquakes
Ridgecrest
Los Angeles
Bakersfield
Las Vegas
Sacramento
San Diego
Tijuana
UTC time 
 A: 2019-07-04 17:33:49
 B: 2019-07-05 11:07:53
 C: 2019-07-06 03:19:52
 D: 2020-06-03 01:32:11
ISC event 
 A: 616042637
 B: 616043696
 C: 616046044
USGS-ANSS 
 A: ComCat
 B: ComCat
 C: ComCat
 D: ComCat
Local date 
 A: July 4, 2019 (2019-07-04)
 B: July 5, 2019 (2019-07-05)
 C: July 5, 2019 (2019-07-05)
 D: June 3, 2020 (2020-06-03)
Local time 
 A: 10:33 a.m. PDT
 B: 4:08 a.m. PDT
 C: 8:19 p.m. PDT
 D: 6:32 p.m. PDT
Magnitude 
 A: Mw6.4[1]
 B: Mw 5.4[2]
 C: Mw 7.1[3]
 D: Mw 5.5[4]
Depth 
 A: 10.7 km (6.6 mi)
 B: 7.0 km (4.3 mi)
 C: 8.0 km (5.0 mi)
 D: 6.8 km (4.2 mi)
Epicenter35.766°N 117.605°W / 35.766; -117.605
TypeStrike-slip
Areas affectedCalifornia, Nevada
Total damageAt least $1 billion
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)

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.[9][8] Effects were felt across much of Southern California, parts of Arizona and Nevada[10], 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.[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.
The aftershocks of the Ridgecrest earthquakes reveal two fault zones. The July 4 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.

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.[12][13] 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.[14] The most populated area near the epicenter was Ridgecrest, home to 28,000 people.[15] 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.[15][16] The rupture occurred along a 10 mi (16 km) section of an unspecified fault. Earth on either side of the fault was deformed, with lateral shifts of 6–8 in (15–20 cm) in the immediate vicinity.[17] 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.[18] Focused at a relatively shallow depth of 6.6 mi (10.7 km), the foreshock affected a large region populated by 20 million people.[14][15] Residents near the epicenter reported that shaking lasted approximately 30 seconds.[18] 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.[15][19]

At 8:19 p.m. PDT on July 5, a larger 7.1 Mw  earthquake occurred in the Ridgecrest area after being preceded by a 5.0 Mw  foreshock 3 minutes prior[20], revealing the previous day's 6.4 Mw  earthquake to have been a foreshock. All three 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 Little Lake Fault Zone.[21]

Aftershocks

A significant series of additional earthquakes followed the foreshock, with the majority of magnitudes ranging approximately 2–4 Mw .[22] By the evening of July 5, more than 1,400 earthquakes occurred,[23] the strongest of which measured 5.4 Mw  at 4:07 a.m. PDT (11:07 UTC) on July 5.[24] 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.[17] The number of aftershocks within hours of the earthquake were unusually high, but not unprecedented.[25]

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.[26] Geologists at the USGS estimate an additional 34,000 aftershocks in the six months following the earthquakes.[27]

On June 3, 2020, at 6:32 PM PST, a 5.5 Mw  aftershock was recorded 11 miles south of Searles Valley. This aftershock is tied for the strongest aftershock following the 7.1  Mw  mainshock.

Events at or above Mw  4.5 associated with the 2019 Ridgecrest earthquakes
Date Time (UTC) Magnitude Mw  MMI Depth Location Ref.
July 417:33:496.4 VIII6.4 mi (10.3 km)7.5 mi (12 km) SW of Searles Valley[14]
July 418:39:444.6 VI1.7 mi (2.8 km)4.3 mi (7 km) ESE of Ridgecrest[28]
July 418:56:064.6 VI1.2 mi (1.9 km)9.3 mi (15 km) NE of Ridgecrest[29]
July 419:21:324.5 VI3.2 mi (5.2 km)8.1 mi (13 km) SSW of Searles Valley[30]
July 511:07:535.4 VII4.3 mi (7.0 km)9.9 mi (16 km) W of Searles Valley[31]
July 603:16:325.0 VII0.6 mi (0.9 km)8.7 mi (14 km) WSW of Searles Valley[32]
July 603:19:537.1 IX5.0 mi (8.0 km)11 mi (18 km) W of Searles Valley[33]
July 603:22:034.6 VII5.7 mi (9.1 km)9.9 mi (16 km) E of Little Lake[34]
July 603:22:485.0 VI5.9 mi (9.5 km)9.9 mi (16 km) ESE of Little Lake[35]
July 603:23:505.4 VII7.7 mi (12.4 km)11 mi (18 km) WNW of Searles Valley[36]
July 603:25:275.0 VI7.0 mi (11.2 km)14 mi (23 km) ESE of Little Lake[37]
July 603:27:064.7 VI8.1 mi (13.0 km)11 mi (18 km) E of Little Lake[38]
July 603:29:294.5 VI6.9 mi (11.1 km)7.5 mi (12 km) SW of Searles Valley[39]
July 603:47:535.5 V2.1 mi (3.4 km)9.3 mi (15 km) ESE of Little Lake[40]
July 603:50:594.9 V4.1 mi (6.6 km)12 mi (19 km) ESE of Little Lake[41]
July 604:13:074.8 VI4.9 mi (7.9 km)3.7 mi (6 km) SE of Ridgecrest[42]
July 604:18:555.4 VII4.6 mi (7.4 km)12 mi (20 km) E of Little Lake[43]
July 604:36:554.9 VII1.2 mi (1.9 km)9.9 mi (16 km) ESE of Little Lake[44]
July 606:01:514.6 VI3.2 mi (5.1 km)9.3 mi (15 km) E of Little Lake[45]
July 608:32:574.6 VI1.9 mi (3.1 km)9.9 mi (16 km) SSW of Searles Valley[46]
July 609:28:284.9 VII2.5 mi (4.0 km)11 mi (17 km) ESE of Little Lake[47]
July 613:06:554.5 VI1.5 mi (2.4 km)11 mi (18 km) E of Little Lake[48]
July 623:50:414.5 VII1.9 mi (3.0 km)14 mi (22 km) N of Ridgecrest[49]
July 705:38:154.5 VI6.6 mi (10.6 km)9.9 mi (16 km) W of Searles Valley[50]
July 1100:14:374.5 VI0.5 mi (0.8 km)9.9 mi (16 km) NNE of Coso Junction[51]
July 1213:11:374.9 VI6.2 mi (9.9 km)5.0 mi (8 km) ENE of Ridgecrest[52]
July 1620:15:364.5 VI2.2 mi (3.6 km)12 mi (19 km) NNE of Ridgecrest[53]
July 1803:59:144.9 VI1.6 mi (2.5 km)5.6 mi (9 km) NE of Coso Junction[54]
July 2600:42:474.7 VI2.4 mi (3.8 km)11 mi (18 km) E of Little Lake[55]
August 2220:49:505.0 VII1.5 mi (2.4 km)11 mi (18 km) E of Little Lake[56]
June 401:32:115.5 VIII4.2 mi (6.8 km)11 mi (17 km) S of Searles Valley[57]

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.[15][58] One mobile home was knocked off its foundation and deemed uninhabitable.[17] Around 20 injuries were reported, primarily from shattered glass and falling debris.[59][58] Some gas lines broke, prompting utility companies to shut off service. Businesses experienced product loss, with goods falling off shelves.[60] Emergency personnel responded to nearly two dozen incidents in the city and opened two shelters.[15] Fifteen patients at Ridgecrest Regional Hospital and residents in several apartment buildings were evacuated.[61] Approximately 6,900 customers lost power near the epicenter: 6,000 in Ridgecrest and 900 in Searles Valley.[62] A 4 in (10 cm) wide crack occurred along State Route 178 near Searles Valley and debris covered part of U.S. Route 395.[63][58] 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.[25] In Los Angeles proper, power outages affected the Fashion District and Granada Hills.[64]

One person died in Pahrump, Nevada, when a lifted Jeep he was working under collapsed.[65]

July 5 mainshock

Several fires broke out and five injuries were reported after the mainshock hit, most of them in Ridgecrest and Trona.[66][67] 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.[9] Roughly 50 homes were damaged in the town.[68] Multiple rockslides also occurred, making all roads to the city impassable. Water was also in high demand.[9][69] CalTrans once again closed State Route 178 after new cracks and rockslides had occurred.[70]

Overall damage is estimated in excess of $5.3 billion.[65][71]

Aftermath

July 4 foreshock

Hours after the Mw  6.4 foreshock, California Governor Gavin Newsom approved an emergency proclamation for Kern County.[72][73] 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.[74] Routine protocol inspections of major infrastructure, including the Los Angeles Aqueduct, were conducted across the Los Angeles metropolitan area.[75] The Ventura County Fire Department dispatched personnel to survey the county for damage.[63] Naval Air Weapons Station China Lake brought in additional personnel to conduct damage assessments.[58] The USGS sent geologists to Kern County soon after the foreshock to look for a surface rupture and collect data.[75] Disneyland suspended ride operations for inspection.[76]

On July 4, seismologist Dr. Lucy Jones said there was a "1 in 20 chance" that the shock would be followed by larger earthquakes over the next few days. Jones also noted that the magnitude of additional shocks would also likely increase, with some possibly exceeding 5 Mw .[75]

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.[9] The agency distributed cots, water, and food. Due to temperatures exceeding 100 °F (38 °C), Cal OES established cooling stations in the affected areas.[68] Newsom proclaimed a state of emergency for San Bernardino County on July 6.[77] 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.[68]

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.[78]

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 and 30 miles in length.[79]

Earthquake early warning

Many residents of Los Angeles County were not pleased when an earthquake early warning mobile app, ShakeAlertLA, did not alert them to either of the Ridgecrest earthquakes, which many people assumed to be failure.[80] This app, developed by the City of Los Angeles in partnership with the USGS, and released at the beginning of 2019, is intended to give users located in Los Angeles County some tens of seconds of warning of possibly damaging shaking from a non-local earthquake.[81] ShakeAlertLA is triggered by the ShakeAlert system being developed by the USGS that monitors earthquakes across Southern California. When that system detects an earthquake of magnitude 5.0 or greater it calculates the intensity of shaking to be expected in Los Angeles County, factoring in the calculated magnitude and distance of the source.[82]

At the time of the Ridgecrest earthquakes the threshold for issuing an alert was an expected shaking intensity in Los Angeles County of 4 (IV) on the Modified Mercalli Intensity Scale, what is considered "light shaking" with only slight damage (such as cracked plaster).[83] The intensity expected for Thursday's quake (on the 4th) was calculated to be less than that, so no alert was issued. While the actual shaking reached intensity 4 in some areas in the northern part of the county, in other parts the intensity reached only a level 2 or 3, not noticed by many people.[84] The second quake, having a greater magnitude, was felt more strongly, with an intensity of 4.5 in some places, and 3.9 downtown.[85]

According to the City of Los Angeles's Twitter account, the threshold will be lowered after this event.[86][87]

Tectonic setting
Red marks the major fault zones. The red zone extending northeast from "LA" is the Garlock Fault. Extending northward from the Garlock Fault are (east-to-west) the Death Valley fault zone (orange), Panamint Valley Fault (red), Little Lake and Airport Lake fault zones (short bit of orange). The White Wolf Fault (yellow) parallels the western end of the Garlock Fault, with the Kern Canyon Fault striking north.

The broad context of the Ridgecrest earthquakes is the Eastern California Shear Zone (ECSZ), a seismically active region east of the southern segment of the San Andreas Fault (SAF) and largely coincident with the Mojave Desert, featuring multiple right-lateral strike-slip faults paralleling the SAF.[88] It is transected by the Garlock Fault, extending northeast and then east from the SAF's "Big Bend" to the Death Valley Fault near the Nevada state line, passing Ridgecrest about fifteen miles to the south.[89]

The ECSZ extends north along the east front of the Sierra Nevada Mountains to Walker Lane, a zone of faulting extending into Nevada and northward, where the Sierra Nevada (Sierran) microplate that underlies most of Central California is being torn away from North American continent.[90] Currently approximately one-quarter of the slippage between the Pacific Plate and North America is accommodated through the ECSZ and Walker Lane;[91] it is expected that eventually the shearing will consolidate into a new transform fault that wll replace the San Andreas Fault.[92]

Along the eastern front of the Sierra Nevada strike-slip faulting happens on the Owens Valley Fault (OVF), part of which ruptured in the 1872 Owens Valley earthquake near Lone Pine. The OVF runs south, largely along U.S. Highway 395, through Bishop, Big Pine, Independence, and Lone Pine to the northern end of Rose Valley and the northwestern corner of the Naval Weapons Center (NWC), where the OVF turns slightly to the east.[93] At the south end of Rose Valley the Little Lake Fault – scene of the 2019 Ridgecrest earthquakes – strikes southeast from near Little Lake[94] (a "locale" at the south end of Rose Valley) to run under the Naval Weapons Center. The surface trace of the Little Lake Fault is mapped through the northeast corner of the City of Ridgecrest, but due to the dip of the fault the epicenters of the 2019 earthquakes are mainly under the NWC, where the Little Lake Fault intersects the broad north-south oriented Airport Lake Fault Zone.[95] The fault continues on to the Garlock Fault about 15 miles southeast of Ridgecrest, just past Searles Station.[96]

East of Rose Valley, between the nearly parallel ends of the Owens Valley and Little Lake faults, lies the Coso Range and Coso Volcanic Field (a notable geothermal field). These lie in a zone where stress and strike-slip movement from the OVF is transferred to various other faults to the south and east, including the Little Lake and Airport Lake faults.[97] The Little Lake Fault has been considered a splay (branch) of the Sierra Nevada (or Sierran) Frontal Fault (SNFF)[98] (formed by the uplift of the Sierra Nevada), but may actually accommodate a significant amount of the right-slip motion of the ECSZ,[99] and (along with the Airport Lake fault zone) may be a major tectonic boundary.[100] South of Little Lake the SNFF continues south along the west side of Indian Wells Valley (where Ridgecrest is situated), then curves west (roughly along California Highway 14) before connecting with the Garlock Fault.[101]

The easterly striking left-slip Garlock Fault south of Ridgecrest is one of California's longest active faults, and marks the boundary between different styles of tectonic deformation.[102] It has been called "somewhat enigmatic" in that it appears to neither offset, nor be offset by, any of the active, NW trending strike-slip faults that cross the ECSZ.[103] In particular, even though the Little Lake Fault is in general alignment with the Blackwater Fault[104] (and its southern extension, the Calico Fault), and a connection is "strongly suspected",[105] and though the aftershocks triggered along the entire length of these faults by the 1992 Landers earthquake suggests a structural continuity,[106] yet the surficial geology shows that "the Blackwater fault ends a few kilometers short of the Garlock fault."[107] How to explain this apparent lack of fault offsetting, and the larger question of how strain (dislocation) is transferred through or around the Garlock Fault, remains unanswered.[103]

Geodetic measurements show that the slip-rate of Garlock Fault is currently less than half of its estimated long-term geological rate.[108] This may indicate that the Garlock Fault is in the late stages of its earthquake cycle.[109]

The Scodie Lineament is a zone of microseismicity extending southwest (paralleling the Garlock Fault) from near Walker Pass (due west of Ridgecrest) to align with the White Wolf Fault, scene of the 1952 Kern County earthquake south of Bakersfield. The nature of the seismicity suggests an early stage in the formation of a strike-slip fault, before localized faulting in the shear zone has connected to form a continuous structure.[110]

Historical seismicity

A large portion of the slippage between the Pacific and North American plates is accommodated in the Eastern California Shear Zone (ECSZ), resulting in many large earthquakes even within the limited span of the historical era.[111] Most notable of these earthquakes is the 1872 Owens Valley earthquake, With an estimated magnitude of 7.4 Mw (preferred; other estimates range as high as 7.9[112]), this earthquake is believed to be the greatest earthquake on record not only for California, but for all of the western United States.[113]

In March 1946 an ML 6.3[114] earthquake struck near Walker Pass (crest of the Sierra Nevada, due west from Ridgecest), with aftershocks continuing for nearly a year.[115] The 1952 Kern County earthquake (Ms7.5, Mw 7.3[116]), considered the biggest earthquake to hit California since the 1906 San Francisco earthquake,[117] occurred on the White Wolf fault south of Bakersfield, and likely connected with the Walker Pass earthquake via the Scodie Lineament.[118]

At the southern end of the ECSZ the 1992 Landers earthquake, at magnitude Mw 7.2 (Ms7.8)[119] was also the strongest earthquake in California since 1906. It was followed by a Mw 7.2 (MS7.4)[120] quake on a nearby fault, the 1999 Hector Mine earthquake.[111] Following the Landers earthquake "a well-developed linear pattern of primary and triggered aftershocks" was observed that extended along the Little Lake Fault and into Owens Valley.[106]

Smaller earthquakes are quite common. In the Ridgecrest area these include a ML5.2[121] earthquake in October 1961 near Brown (approximately halfway between Ridgecrest and Little Lake) that was felt in Independence and Los Angeles; it was preceded by eight minutes by an ML 3.4 foreshock felt in China Lake (east of Ridgecrest).[122] Additional earthquakes struck near Walker Pass in 1961 (ML 5.3),[123] 1962 (ML 4.9),[124] and 1979 (ML 4.3).[125] In 1977 two small quakes that hit Ridgecrest in February[126] were followed by another pair of small earthquakes in March.[127]

Seismicity in Indian Wells Valley has been characterized by swarms of thousands of earthquakes, some lasting for more than a year.[128] The Ridgecrest earthquake sequence of 1995 was particularly notable, having eight events M ≥ 4.0. This sequence was similar to the 2019 earthquakes in having two main shocks: an ML 5.4 earthquake on August 17 located 11 miles north of Ridgecrest,[129] and an ML 5.8 earthquake on September 20, located about a mile south-southwest of the first earthquake.[130] Another shock on the 24th was ML 4.9. Another similarity with the 2019 events: the first earthquake, although occurring on a north-northwest trending fault (presumably the Little Lake fault), may have involved a northeast-striking fault.[130]

An earlier study[131] noted that successive earthquake sequences here tend to increase in number and magnitude, and migrate southward.

gollark: 170.
gollark: Hmm, as vaguely inelegant as it might be, maybe have the code store 1 to 3 (0 to 2) and then convert that to three brightness levels separately.
gollark: Besides, your code says 254, not 255.
gollark: Why do you need exactly and specifically that?
gollark: It might be a rounding error. This is why integers.

See also

References
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  2. ANSS: Ridgecrest 2019b.
  3. ANSS: Ridgecrest 2019c.
  4. ANSS: Ridgecrest 2019d.
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  6. ANSS: Ridgecrest 2019a, "Regional Information".
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  40. "M 5.5 - 15km ESE of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  41. "M 4.9 - 19km ESE of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  42. "M 4.8 - 6km SE of Ridgecrest, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  43. "M 5.4 - 20km E of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  44. "M 4.9 - 16km ESE of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  45. "M 4.6 - 15km E of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  46. "M 4.6 - 16km SSW of Searles Valley, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  47. "M 4.9 - 17km ESE of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  48. "M 4.5 - 18km E of Little Lake, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  49. "M 4.5 - 22km N of Ridgecrest, CA". United States Geological Survey. July 6, 2019. Retrieved July 10, 2019.
  50. "M 4.5 - 16km W of Searles Valley, CA". United States Geological Survey. July 7, 2019. Retrieved July 10, 2019.
  51. "M 4.5 - 16km NNE of Coso Junction, CA". United States Geological Survey. July 11, 2019. Retrieved July 11, 2019.
  52. "M 4.9 - 9km ENE of Ridgecrest, CA". United States Geological Survey. July 12, 2019. Retrieved July 11, 2019.
  53. "M 4.5 - 19km NNE of Ridgecrest, CA". United States Geological Survey. July 16, 2019. Retrieved July 26, 2019.
  54. "M 4.9 - 9km NE of Coso Junction, CA". United States Geological Survey. July 16, 2019. Retrieved July 26, 2019.
  55. "M 4.7 - 18km E of Little Lake, CA". United States Geological Survey. July 26, 2019. Retrieved July 26, 2019.
  56. "M 5.0 - 18km E of Little Lake, CA". United States Geological Survey. August 22, 2019. Retrieved August 23, 2019.
  57. "M 5.5 - 17km S of Searles Valley, CA". United States Geological Survey. June 3, 2020. Retrieved June 3, 2020.
  58. "No major injuries reported in 6.4 earthquake in California's Mojave Desert". KSBY. July 4, 2019. Retrieved July 4, 2019.
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  61. John Antczak and Olga R. Rodriguez (July 4, 2019). "Some injuries, 2 house fires after quake". News Channel 9. Associated Press. Retrieved July 4, 2019.
  62. Alicia Robinson and Jeong Park (July 4, 2019). "6.4 magnitude earthquake near Ridgecrest felt throughout Southern California". The Sun. Retrieved July 4, 2019.
  63. 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.
  64. "6.4M Quake Strikes Near Ridgecrest In Kern County; No Reports Of Damage In LA". CBSLA. July 4, 2019. Retrieved July 4, 2019.
  65. 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.
  66. McBride, Jessica (July 6, 2019). "Trona, California Suffers Earthquake Damage, Rockslides". Heavy.com. Retrieved July 6, 2019.
  67. Maxouris, Christina; Moon, Sarah; Jones, Sheena. "Fires break out after a second and stronger earthquake hits Southern California". CNN.
  68. Christine Kim and Jonathan Lloyd (July 8, 2019). "Clusters of Jarring Aftershocks Shake Ridgecrest With Thousands More Expected". NBC Los Angeles. Retrieved July 10, 2019.
  69. Chabria, Anita; Reyes-Velarde, Alejandra; Vives, Ruben. "Earthquake batters Trona: Rockslides cut off town; water is scarce". latimes.com.
  70. "Caltrans District 9". www.facebook.com.
  71. Los Angeles Times (August 14, 2019). "Ridgecrest Quake Damage Estimated Above $5 Billion at Massive China Lake Naval Base". KTLA. Retrieved August 23, 2019.
  72. Newsom, Gavin [@CAgovernor] (July 4, 2019). ".@GavinNewsom has approved an emergency proclamation for the 6.4 magnitude earthquake in Kern County & aftershocks. @Cal_OES has been fully activated since this morning & is working closely with state & local emergency managers to respond to impacts to residents & infrastructure" (Tweet) – via Twitter.
  73. Gudel, Jonathan (July 4, 2019). "Cal OES Activates SOC in Support of Ridgecrest Earthquake in Southern California". California Governor's Office of Emergency Services. Archived from the original on July 6, 2019. Retrieved July 6, 2019.
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  78. "Naval Air Weapons Station China Lake". www.facebook.com. Retrieved July 7, 2019.
  79. KAPLAN, KAREN (July 6, 2019). "Nearly 11% chance of another earthquake of magnitude 7 or greater in Southern California, scientists say". latimes.com.
  80. Bogel-Burroughs, Nicholas (July 8, 2019). "Californians' Alert Apps Didn't Sound for 2 Big Earthquakes. Why Not?". New York Times.; Dowd, Katie (July 4, 2019). "ShakeAlert fails to send earthquake warning for big SoCal quake". SFGate. Retrieved July 4, 2019.
  81. More distant earthquakes provide more warning, but are less damaging, than local earthquakes.
  82. Given et al. 2018.
  83. Lin, Rong-Gong, II (July 4, 2019). "Why L.A.'s early warning system didn't send an alert before the 6.4 magnitude quake". Los Angeles Times. Retrieved July 4, 2019.
  84. Los Angeles Times, July 4, 2019.
  85. New York Times, July 8, 2019.
  86. "ShakeAlertLA to Lower Alert Threshold After 6.4 Magnitude Quake Hits Mojave Desert, City Says". KTLA. July 4, 2019. Retrieved July 4, 2019.
  87. City of Los Angeles [@LACity] (July 4, 2019). "The #ShakeAlertLA app only sends alerts if shaking is 5.0+ in LA County. Epicenter was 6.4 in Kern County, @USGS confirms LA's shaking was below 4.5. We hear you and will lower the alert threshold with @USGS_ShakeAlert" (Tweet). Retrieved July 4, 2019 – via Twitter.
  88. Frankel et al. 2008, p. 45, and see Figure 1; Wesnousky 2005, p. 3369.
  89. The ECSZ was originally limited to the area south of the Garlock Fault, which separates distinctly different modes of deformation, but now is considered to extend into Walker Lane. Miller et al. 2001, pp. 2255, 2245.
  90. Frankel et al. 2008, p. 1671.
  91. Frankel et al. 2008, p. 45; Miller et al. 2001, p. 2260.
  92. Faulds, Henry & Hinz 2005, p. 508.
  93. See Figure 1 (index map) in Frankel et al. 2008, p. 46.
  94. Zellmer 1987, pp. 5, 10, and see figure 2 (p. 9) for a map of the area.
  95. Zellmer 1987, pp. 7, 10, and see Figure 2 (p.6), "Generalizied Geologic Map of the Indian Wells Area".
  96. Roquemore 1981a, pp. 2, 14.
  97. Frankel et al. 2008, p. 56; Hauksson & Unruh 2007, para. 61.
  98. Roquemore 1981a, p. 14, §2.2.
  99. Hearn & Humphreys 1998, p. 27,034; Zellmer 1987, p. 10.
  100. Unruh, Humphrey & Barron 2003, p. 328.
  101. Frankel et al. 2008, Figure 1.
  102. Zellmer 1987, p. 12; Miller et al. 2001, p. 2254.
  103. Frankel et al. 2008, p. 45.
  104. Roquemore & Simila 1994, p. 860.
  105. Dokka & Travis 1990, p. 315.
  106. Roquemore & Simila 1994, p. 854.
  107. Roquemore & Simila 1994, p. 854. See also figure 4 in Dokka & Travis (1990, p. 314) showing the northern termination of the Blackwater fault.
  108. McClusky et al. 2001, p. 3371.
  109. Miller et al. 2001, p. 2259.
  110. Bawden, Michael & Kellog 1999, pp. 603, 604.
  111. Miller et al. 2001, p. 2245.
  112. Hough & Hutton 2008, p. 932.
  113. Roquemore 1981a, p. 75, 5.2.1.
  114. Stover & Coffman 1993, pp. 83, 138.
  115. Roquemore 1981a, p. 77, 5.2.3.
  116. ISC-OB Event 893168 [IRIS].
  117. Bawden 2001, p. 771.
  118. Bawden, Michael & Kellog 1999, p. 602.
  119. ISC-EHB Event 289086 [IRIS].
  120. ISC-EHB Event 1643776 [IRIS].
  121. Stover & Coffman 1993, p. 89.
  122. Roquemore 1981a, p. 84, 5.2.5.
  123. Stover & Coffman 1993, pp. 89, 151.
  124. Stover & Coffman 1993, p. 90; Roquemore 1981a, p. 86, 5.2.6.
  125. Stover & Coffman 1993, p. 94; Roquemore 1981a, p. 93, 5.2.9.
  126. Roquemore 1981a, p. 90, 5.2.7.
  127. Roquemore 1981a, p. 92, 5.2.8.
  128. Hauksson et al. 1995, p. 54, and see Figure 1, p. 55.
  129. Hauksson et al. 1995, p. 54.
  130. Hauksson et al. 1995, p. 58.
  131. Roquemore & Zellmer 1983, p. 7.

Scientific sources
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