M 6.4 and M 7.1 Ridgecrest, CA Earthquakes
VIRTUAL ASSESSMENT STRUCTURAL TEAM (VAST) REPORT

Damaged mobile home in Ridgecrest, CA during the M 6.4 earthquake. Photo by Darla A. Baker / The Californian.

VAST Authors
Lead Author: Khalid M. Mosalam, University of California, Berkeley
Co-Authors (in alphabetical order)

Veronica Abuchar, Universidad del Norte
Jorge Archbold, University of California, Berkeley
Carlos A. Arteta, Universidad del Norte - CEER
Erica C. Fischer, Oregon State University
Selim Günay, University of California, Berkeley
Manny Hakhamaneshi, Caltrans & Cal State East Bay
Wael M. Hassan, University of Alaska, Anchorage
Laura Micheli, Iowa State University
Sifat Muin, University of California, Berkeley
Cesar Pajaro, Universidad del Norte
Renmin Pretell, University of California, Davis
Han Peng, Harbin Institute of Technology
Ian Robertson, University of Hawaii
Katerina Ziotopoulou, University of California, DavisXavier Vera,

VAST Editors(in alphabetical order)
David Roueche
Auburn University

GeoEstudios and UCSG, Ecuador

Released: July 8, 2019 | NHERI DesignSafe Project ID: PRJ-2444

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Executive Summary
A magnitude 6.4 earthquake with a depth of 10.7 km occurred in San Bernardino County, CA on
July 4, 2019. The epicenter was located 12 km south west of Searles Valley. On July 5, 2019, a
7.1 magnitude earthquake occurred near the same location and at a depth of 17 km. It is notedthat the earthquakes occurred in a fairly remote area in the Mojave Desert region of eastern
California. The earthquakes were felt strongly in the China Lake-Ridgecrest area, and more
broadly from Los Angeles to Las Vegas. The 6.4 magnitude earthquake was preceded by several
foreshocks and followed by hundreds of aftershocks. The maximum Peak Ground Accelerations(PGA) of the 6.4 and 7.1 magnitude earthquakes were 0.38g and 0.48g, respectively. In thisreport, the PGA residuals are estimated using the ASK14 GMPE in terms of the number ofstandard deviations with respect to the median model, which correlates to structural response
due to earthquake ground motions.
The impact of the two earthquakes on the city of Ridgecrest demonstrated its resiliency as it
recovered rapidly where many restaurants and gas stations are back up and running. There wasvery little structural damage, even from the second stronger earthquake of M 7.1, except for the
typically vulnerable buildings (e.g. unreinforced masonry structures and mobile homes). However,there were substantial non-structural and content losses. Fortunately, both earthquakes occurred
during a holiday weekend, which meant that schools were not in session and most offices were
not operational during the events. If it had not been a holiday and these schools and office spaces
would have been fully occupied or the earthquake occurred in a more urban area, fatalities/injuries
due to these non-structural damages could have been larger. As a community, we have to beprepared for those scenarios as well. Once again, these two earthquakes have proven the needto improve our regulations when it comes to the design of non-structural components.
Moreover, some utilities for electricity and water distribution suffered from distress. On the other
hand, transportation systems and bridges suffered none to minor damage with effective and rapid
repair actions.
The other city that was impacted the most is Trona, which did not perform as resilient as
Ridgecrest where the city remained dysfunctional up to the time of writing this report. There weremore damaged structures, mostly from the effects of ground failure and possibly strong site
response related to soft sediments. The town suffered from significant loss of water where its
main water pipes fractured due to fault rupture and lateral spreads.
This report overviews the hazard characteristics of the July 4 and 5, 2019 Ridgecrest, California
M 6.4 and M 7.1 earthquakes, the regulatory context and emergency response, the impacts ofthese earthquakes, and current conditions by collocating publicly-reported information. This
Preliminary Virtual Reconnaissance Report (P-VRR) represents the first product of StEER’s larger
coordinated response to this event, informing and supporting other research teams seeking tolearn from this disaster.

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TABLE OF CONTENTS
Executive Summary

2

TABLE OF CONTENTS

3

Introduction

5

Earthquake Details and Tectonic Summary

1

Historical Context

2

Recorded Ground Motions

3

PGA Residuals

7

Local Codes and Construction Practices

10

Federal, State and Local Response

12

Federal Response

12State Response

12

Local Response

12

Impacts

14

Loss of Life and Injuries

14

Buildings

15

Critical Facilities

15

Commercial Construction

15

Residential Construction

18

Schools

24

Instrumented Structures

25

Fire Following Earthquake27

M 6.4 Earthquake - July 4, 201927

M 7.1 Earthquake - July 5, 201928

Lifelines

29

Transportation Infrastructure and Bridges

29

Utilities for Electricity and Water Distribution

36

Non-Structural Damage

38

Geotechnical Failures39

M6.4 Earthquake - July 4, 201939

M7.1 Earthquake - July 5, 201941

Current Conditions, Access Restrictions and Recommendations
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3

StEER Response Strategy

47

Appendix A: Expected Earthquake Performance of Buildings Designed to the California Building
Code48
Appendix B: EERI VERT Report

52

References

70

Acknowledgements

71

About StEER72

StEER Event Report Library72

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance4Introduction
On July 4, 2019 at approximately 10:33 am PDT, a magnitude 6.4 earthquake with a depth of
10.7 km occurred in a remote area of San Bernardino County, CA. The epicenter was located 12
km south west of Searles Valley at coordinates of 35.71°N and 117.51°W. On July 5, 2019 at 8:19
pm, approximately 34 hours after the first earthquake, a 7.1 magnitude earthquake occurred near
the same location, with coordinates of 35.77°N 117.61°W. The 7.1 magnitude earthquake had adepth of 17 km. Since the events were not close to urban areas, the damage experienced bybuildings and other infrastructure was not extensive. However, this earthquake sequence is quite
important as it includes the two largest earthquakes that occurred in Southern California in thepast two decades. It provides many opportunities to learn about the following, among several
other useful lessons: a) the earthquake sequence characterized by two large magnitude
earthquakes one day apart, and relevantly the large magnitude foreshock scenario, b) the
performance and impact of the Earthquake Early Warning and ShakeAlertLA systems, c) the
expected performance in future earthquakes of pre-1980 non-ductile reinforced concretebuildings, the pre-1980 soft-first story buildings, the water system infrastructure, and thetelecommunications infrastructure, which were identified as four areas of seismic vulnerability by
the LA Mayoral Seismic Task Force, d) the efficacy of the adopted retrofit techniques in improving
structural response, e) the performance of various structures, including school buildings,
hospitals, large industrial facilities, regional airports, and mobile homes, f) the significance of nonstructural damage, g) the ground motion characteristics, and h) the community resilience in termsof the duration of power outages, mobile phone network access, infrastructure repairs, etc.
StEER further hopes to use this event to exercise protocols, procedures, policies and workflowsthat StEER will be developing over the next year in collaboration with the wider hazards
community including the Natural Hazards Engineering Research Infrastructure (NHERI) and othermembers of the Extreme Events Reconnaissance Consortium.
The first product of the StEER response to the 2019 Ridgecrest, California Earthquakes is thisPreliminary Virtual Reconnaissance Report (PVRR), which is intended to:
1. provide an overview of the hazard characteristics
2. introduce the regulatory and disaster response context for these events
3. summarize the preliminary reports of damage to wide-ranging infrastructure
4. review StEER’s event strategy in response to these earthquakes
5. enhance situational awareness to guide subsequent missions conducted by StEER
and the engineering reconnaissance community
It should be emphasized that all results herein are preliminary and based on the rapid
assessment of publicly available online data within 3-4 days of these events. Damage
assessments discussed herein are based largely on the judgement of the authors without
access or with very preliminary and limited access to additional aerial imagery and groundtruthing.

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance5Earthquake Details and Tectonic Summary
On July 4, 2019 at approximately 10:33 am PDT, a magnitude 6.4 earthquake with a depth of
10.7 km occurred in a remote area of San Bernardino County, CA. The epicenter was located 12
km south west of Searles Valley at coordinates of 35.71°N and 117.51°W. On July 5, 2019 at 8:19
pm, approximately 34 hours after the first earthquake, a 7.1 magnitude earthquake occurred near
the same location, with coordinates of 35.77°N 117.61°W. The 7.1 magnitude earthquake had adepth of 17 km.
The earthquakes were felt strongly in the China Lake-Ridgecrest area, and more broadly from
Los Angeles to Las Vegas. The 6.4 magnitude earthquake was preceded by several foreshocks,
and hundreds of aftershocks were detected after the mainshocks. USGS ShakeMap (Figure 1)
indicates the maximum Peak Ground Accelerations (PGA) of the 6.4 and 7.1 magnitude
earthquakes in the range of 0.2 to 0.3g and 0.7 to 0.8g, respectively. Recorded motions are in asimilar range for the 6.4 magnitude earthquake, however for the 7.1 magnitude earthquake, they
are on the order of 0.5g, which is less than those predicted by ShakeMap.

Figure 1. Epicenters of the two Ridgecrest earthquakes and Shakemaps [Left: M 6.4 eventand right: M 7.1 event] (USGS, 2019a; USGS, 2019b)
Both earthquakes occurred as the result of shallow strike-slip faulting in the crust of the North
America plate. According to the focal mechanism solutions, rupture occurred on a steeply dipping
fault as the result of either right lateral (RL) slip on a plane striking NW-SE, or as left lateral (LL)slip on a plane striking SW-NE. The earthquakes were located approximately 150 km northeastof the San Andreas Fault - the major plate boundary in the region. At the locations of theearthquakes, the Pacific plate is moving to the northwest with respect to the North America plate
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at a rate of approximately 48 mm/yr. The location of the earthquakes falls within the Eastern
California shear zone, a region of distributed faulting associated with motion across the PacificNorth America plate boundary, and an area of high seismic hazard. More detailed studies will be
required to precisely identify the causative fault associated with these events, though seismic
activity over the past 2 days has been occurring on two conjugate fault structures in the Airport
Lake Fault Zone (USGS, 2019a; USGS, 2019b).
The earthquakes have been followed by numerous aftershocks, the largest of which was a
Magnitude 5.4 earthquake 16 hours after the M 6.4 event. Most aftershocks align in a SW-NE
trend around the M 6.4 earthquake, though some also align on a NW-SE trend. The M 6.4 event
was also preceded by a series of foreshocks over the previous hour, including a magnitude 4.0
event about 30 mins earlier.

Historical Context
This region of eastern California has hosted numerous moderate sized earthquakes. Over the
past 40 years, 8 other earthquakes, with magnitudes 5 or larger, have occurred within 50 km of
the July 4th, 2019 earthquake. Figure 2 provides a timeline of historical earthquakes in California
since 1900. The largest earthquake that took place close to the fault that produced the July 4th
and 5th events in the last four decades prior to these two recent events was a magnitude 5.8
event on September 20, 1995, about 13 km to the west-northwest of the July 4th earthquake(USGS, 2019a; USGS, 2019b).
California is a seismically active region that has seen several major earthquakes in recent history.
In 1906 The Great San Francisco Earthquake struck the bay area causing great material andhuman losses. On June 29th, 1925, a M 6.8 earthquake struck in the vicinity of Santa Barbara.
As a consequence of this event the Pacific Building Official Conference (currently the International
Conference of Building Officials) adopted the Uniform Building Code.
In 1933 the city of Long Beach felt a destructive earthquake, which caused 15 schools in the area
to collapse and damaged many more structures. Almost forty years later, in 1971, a M 6.5
earthquake struck the San Fernando Valley. Because of the earthquake, 64 people lost their lives,
over 2000 were injured and damage was estimated at $500+ million. The M 6.9 Loma Prieta
earthquake on October 17, 1989 led to 63 deaths, 3757 people injured and over $5.6 billion indamage. In 1994, the M 6.7 Northridge earthquake led to 57 deaths, over 8700 people injured
and economic losses between $13 and $40 billion.

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Figure 2. Timeline of major earthquakes in California in the 20th and 21st centuries1

Recorded Ground Motions
For both the M 6.4 and M 7.1 events, ground motions were recorded at several stations. In bothcases, the maximum recorded Peak Ground Acceleration (PGA) was recorded at the Christmas
Canyon China Lake station (code CCC). For the M 6.4 event, the PGA was 369 cm/s 2 (0.38g)
and Peak Ground Velocity (PGV) was 27 cm/s according to the Center for Engineering Strong
Motion Data (CESMD) database. For the M 7.1 event, the recorded PGA was 470 cm/s 2 (0.48g)
and PGV was 55.1 cm/s. Figure 3(a) shows the acceleration time series of the ground motions
recorded at the CCC stations for the M 6.4 event and Figure 3(b) shows the same for the M 7.1
event.

1 https://earthquake.usgs.gov/earthquakes/search/

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Figure 3. Acceleration time histories recorded at the Christmas Canyon China lake (CCC)
station from (a) M 6.4 event and (b) M 7.1 event
Figure 4 shows the PGA vs Distance plots for all the recorded ground motions for both events.
The plot shows that beyond a distance of 40 km, the PGA values were less than 0.1g for theforeshock but for the main shock even beyond 100 km, PGA greater than 0.1g has been recorded.
In general, higher PGAs were recorded for longer distance for the M 7.1 event. This is consistent
with the reports of shaking felt throughout the state.
Response spectra (5% damped) of the two horizontal components and the vertical component of
the ground motion with the largest PGA, at the Christmas Canyon China Lake station (code CCC),
are shown in Figure 5. The highest spectral acceleration for this station is computed to be 1.17g
at about 0.48 sec period for the M 6.4 event, Figure 5(a). For the M 7.1 event, Figure 5(b), themaximum spectral acceleration was computed as 1.69g at about 0.11 sec period. Long period
effect was observed in the response spectra of the mainshock.

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Figure 4. Maximum horizontal ground motion versus distance compared with Boore &Atkinson (2008) Ground Motion Prediction Equation (GMPE) for (a) M 6.4 event and (b) M
7.1 event where distance is fault distance if available, otherwise epicentral distance2
2 https://strongmotioncenter.org/graphtest/?iqrid=ci38443183

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5

(a)

(b)
Figure 5. 5% damped response spectra at the CCC station for the (a) M 6.4 event and (b) M
7.1 event (Source: X. Lu, Tsinghua University & also similar to that reported in the CESMD
database3)

3 https://strongmotioncenter.org/NCESMD/data/ci38443183/ciccc.gif

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PGA Residuals
PGA residuals are estimated using the ASK14 GMPE (Abrahamson et al., 2014), in terms of thenumber of standard deviations (i.e. epsilon) with respect to the median model. The variable
epsilon has been shown to be correlated to structural response for mathematical models
subjected to earthquake ground motions (Baker and Cornell, 2008), hence it is deemed
appropriate for the purpose of this report. Equation 1 defines the variable epsilon as follows:
𝜀 (𝑇) =

𝑙𝑛(𝑆𝑎(𝑇)) − 𝑙𝑛(𝜇(𝑇))𝜎𝑙𝑛(𝑇)(1)

where Sa(T) is the measured spectral acceleration at the structural period T, 𝜇(𝑇) is the medianmodel prediction, and 𝜎𝑙𝑛(𝑇) is the GMPE total standard deviation. Data for PGA was obtained
from the USGS event pages (USGS, 2019a; USGS, 2019b). According to Equation 1, positive 𝜀values indicate that the model underpredicts the observations. Figure 6 shows the relative locationof the stations (red markers) with respect to the events epicenters (black stars). For the estimationof the median ground motion prediction model, a Vs30 = 360 m/s is selected for this preliminary
report. Figure 7 shows the stations superimposed on the slope-based Vs30 map of California.

(a)

(b)

Figure 6. Stations location of the two Ridgecrest earthquakes and Shakemaps for (a) M 6.4
event and (b) M 7.1 event

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Figure 7. Stations locations superimposed on the slope-based Vs30 map of California
Figure 8 presents epsilon values versus distance for PGA of the two events. At the closer distance
range (e.g., R ≤ 50 km), the median PGA is estimated by the GMPE without much bias (|𝜀(𝑇)| ≤0.1) for both event magnitudes. In the distance range 100≤ R ≤ 250 km, the median recorded
PGA is larger than the median model, but with a small bias (𝜀(𝑇) ≤ 0.8) for the M 6.4 event. On
the other hand, for the M 7.1 event, the median model agrees with the median recorded data. For
the larger distance range (e.g., R ≥ 400 km), the observations are larger than the median modelby approximately one standard deviation, which is consistent with the observations in Figure 4.

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Figure 8. Epsilon of PGA versus distance, based on the ASK14 ground motion model [Left:
M 6.4 event and right: M 7.1 event]

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance9Local Codes and Construction Practices
Design of new buildings in California is based on the California Building Code. One of the notable
regulations in Southern California is the LA Non-Ductile Reinforced Concrete Ordinance, which
requires mandatory retrofits of reinforced concrete construction. A 4-page brochure developed by
the Pacific Earthquake Engineering Research (PEER) Center in Collaboration with California
Seismic Safety Commission (CSSC) summarizing, in simplified terms, the expected earthquake
performance of buildings designed to the California building code can be found in Appendix A ofthis report.
The California Building Code has seen distinct improvements after each major earthquake. For
example, after the 1971 San Fernando earthquake, seismic detailing was introduced forreinforced concrete members to increase ductility and energy dissipation capacity. Similarly, after
the 1989 Loma Prieta and 1994 Northridge earthquakes, there were improvements related to softstory wood frame buildings and welded steel connections. July 4 and 5 earthquakes also havethe potential to lead to changes in the code, such as the consideration of large aftershocks and avariety of earthquake consequences in seismic design and reinforcing the ongoing efforts towards
changing the code objectives from life safety to community resilience.
Table 1 provides the distribution of housing units by year of construction in San Bernardino County
and the city of Ridgecrest, the most heavily impacted areas. This is based on data from the U.S.
Census Bureau, 2013-2017 American Community Survey 5-Year Estimates (Bureau, 2018). Suchinformation adds context to building performance relative to code changes. It can be seen fromthe table that 47.4% and 53.7% of building stock in San Bernardino County and Ridgecrest City,
respectively, was constructed prior to 1980; i.e. about half the building stock lacks seismic details.
The percentage of seismically retrofitted structures among this deficient building stock is not
currently available.

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Table 1. Distribution of housing units by year of construction in San Bernardino County
and the city of Ridgecrest (U.S. Census Bureau, 2013-2017 American Community Survey
5-Year Estimates (Bureau,2018) )Time Period

San Bernardino County, CA

Ridgecrest, CA

Built 2014 or later

0.50%

0.00%

Built 2010 to 2013

1.50%

1.40%

Built 2000 to 200914.80%

5.90%

Built 1990 to 1999

13.10%

8.20%

Built 1980 to 1989

22.80%

30.80%

Built 1970 to 1979

17.50%

29.40%

Built 1960 to 1969

10.70%

10.20%

Built 1950 to 1959

11.50%

10.90%

Built 1940 to 1949

4.00%

1.60%

Built 1939 or earlier

3.70%

1.60%

Total Housing Units

711,900

12,534

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance11Federal, State and Local Response
Post-earthquake responses by federal, state and municipalities, including Ridgecrest, Trona and
Los Angeles, are presented below.

Federal Response
United States President Trump tweeted about the 4th of July 2019 California earthquake. His
post on Twitter on the same day of the seismic event expressed that the situation seems to beunder control. On July 5th, 2019 Federal Emergency Management Agency delivered a tractortrailer with water bottles to San Bernardino County due to the damage in the water lines 4.

State Response●●●●

On July 4, 2019 California Governor Gavin Newsom declared a state of emergency for
Kern County and expressed that officials are monitoring the aftershocks5.
On July 5th, 2019 Gavin Newsom declared a state of emergency for San Bernardino
County after the M 7.1 earthquake due to conditions of “extreme peril to the safety of
persons and property”6.
Mark Ghilarducci, the Director of the California Governor’s Office of Emergency Services(Cal OES), said that there were no reported deaths or serious injuries7.
The State’s Office of Emergency Services (OES), confirmed that the OES would provide
fire and rescue resources to the affected region8.

Local Response
●
●
●
●

●

Ridgecrest’s Mayor Peggy Breeden declared a state of emergency. Authorities did notreport serious injuries or deaths, but fires, cracked roads, and minor injuries werereported9.
Ridgecrest Regional Hospital was evacuated for evaluation by state inspectors and as apreventive measure due to aftershocks10.
The Red Cross established evacuation centers in Ridgecrest.
On July 5th 2019, Los Angeles Department of Water declared that qualified personnel
were surveying the aqueduct and reservoirs according to their standard earthquake
response protocol. Critical facilities were also being inspected. They declared no damages
were reported at that time11.
According to the pronouncement of the Chief of San Bernardino County Fire Department,

4 https://abc7.com/state-of-emergency-in-san-bernardino-co-after-ridgecrest-quake/5381855/
5 https://abcnews.go.com/US/powerful-aftershocks-shake-southern-california-massive-earthquake-panic/story?id=64147691
6 https://abc7.com/state-of-emergency-in-san-bernardino-co-after-ridgecrest-quake/5381855/
7 https://abcnews.go.com/US/powerful-aftershocks-shake-southern-california-massive-earthquakepanic/story?id=64147691
8 https://www.washingtonpost.com/nation/2019/07/05/aftershocks-rattle-california-after-magnitudeearthquake/?noredirect=on&utm_term=.9c300804d773
9 https://www.washingtonpost.com/nation/2019/07/05/aftershocks-rattle-california-after-magnitudeearthquake/?noredirect=on&utm_term=.cb2f92d75a8c
10 https://www.cnn.com/us/live-news/earthquake-california-july-2019/index.html
11 https://www.latimes.com/local/lanow/la-me-earthquake-california-shake-quake-20190704-story.html
PVRR: Preliminary Virtual Reconnaissance Report
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consisted of collapsed chimneys, mobile homes shaken off their supports and some water
main breaks, including two main lines. Villarino stated that there were no injuries12.
After the M 6.4 earthquake, three important cracks formed across State Route 178 near
Trona. They were temporarily repaired soon after the seismic event13.

12 https://www.latimes.com/local/lanow/la-me-ln-trona-earthquake-20190705-story.html
13 https://www.latimes.com/local/lanow/la-me-ln-trona-earthquake-20190705-story.html

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Impacts
Loss of Life and Injuries
The PAGER (Prompt Assessment of Global Earthquakes for Response) product of the USGS is
an automated system that produces content concerning the estimated impact of significant
earthquakes around the world, informing emergency responders, government and aid agencies,
and the media of the scope of the potential disaster. PAGER rapidly assesses earthquake impacts
by comparing the population exposed to each level of shaking intensity with models of economic
and fatality losses based on past earthquakes in each country or region of the world (USGS,
2019a & 2019b).
PAGER produces rough estimates of the probability density functions of the number of fatalities
and economic losses in U.S. dollars. More specifically, these approximate probability density
functions provide estimates of the probabilities of the order of magnitude of the number of fatalities
and economic losses by providing probabilities within specific ranges each varying an order ofmagnitude from the previous one. The number of shaking-related fatalities in this event was
projected as relatively low according to the USGS (Figures 9(a) and 10(a)) compared to previous
earthquakes with similar magnitude. For both earthquakes, the USGS PAGER tool (Figures 9(b)and 10(b)) estimated no fatalities and 1 to 10 fatalities with probabilities of 65% and 30%,
respectively. At the time of the writing of this report, there were no fatalities. For the 6.4 magnitude
earthquake, PAGER estimated economic losses due to damage to be between $1 million and$10 million, between $10 million and $100 million, and between $100 million and $1,000 million
with probabilities of 27%, 35%, and 21%, respectively. For the 7.1 magnitude earthquake, theseprobabilities were 23%, 35%, and 25%. Similarity of these two sets of estimates for the twoearthquakes despite their significant differences in magnitude is worth exploring. One reason is
the low population density in the epicentral region, and the relatively distant location from large
urban centers.
PAGER reported that some damage is possible and the impact would be relatively localized.
Estimated economic losses are less than 1% of GDP of the United States. Past events with thisalert level have required a local or regional level response. It should be noted that these economic
loss estimates are characterized by even larger variabilities than those in their estimates of thenumber of fatalities.

(a)

(b)

Figure 9. PAGER Estimated probability of (a) fatalities and (b) economic losses for the July
4th, 2019 Ridgecrest, California Earthquake (USGS, 2019a)

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(a)

(b)

Figure 10. PAGER Estimated probability of (a) fatalities and (b) economic losses for the July
5th, 2019 Ridgecrest, California Earthquake (USGS, 2019b)

Buildings
Critical Facilities
Based on most images and reports of damage at Ridgecrest Hospital, it has been evacuatedpredominantly as a precautionary measure14. “Ridgecrest Regional Hospital was evacuated soan engineer could assess whether it had structural damage,” according to Ridgecrest police Capt.
Justin Dampier. According to OSHPD, they inspected the hospital and did not require evacuation.
At the time of authoring this report, Kern County Fire Department (KCFD) reported at least 15
patients were moved to the Ridgecrest High School gymnasium due to “structure” damage at thehospital15. Authorities also stated that about 15 patients were moved to other emergency rooms16.
Those who were evacuated were sheltering in place under shade awnings and trees, while the
15 emergency room patients were taken to Palmdale-Lancaster area. There was no estimate on
how many people in total were evacuated from the hospital17. “There was some structural damage
at the hospital, including leaking sprinklers,” a fire battalion chief said at an afternoon news
conference. Some reports indicated that a building inspector was examining the damage. The
hospital was reported 100% functional again on July 7th.
Commercial Construction
During the two earthquakes, many unsecured objects fell from shelves (Figures 11 to 13). Insideconvenience stores aisles were flooded with broken liquor bottles and food items that had fallen
off the shelves. There was also light to moderate non-structural component damage, such as
collapse of suspended ceilings tiles/grids, concrete, glass and masonry facades, etc. (Figures 14
and 15). As with residential construction covered in the next section, several commercial masonry
structures experienced various degrees of damage, Figure 16.

14 https://www.ridgecrestca.com/news/20190705/breeden-declares-state-of-emergency-following-

earthquake
15 https://www.visaliatimesdelta.com/story/news/2019/07/04/earthquake-centered-kern-county-rattlesvisalia-tulare/1650393001/
16 https://www.nbcnews.com/news/us-news/6-4-magnitude-earthquake-shakes-southern-californian1026621
17 https://ktla.com/2019/07/04/ridgecrest-hospital-evacuated-after-magnitude-6-4-earthquake-hits-nearby/
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Figure 11. Items knocked from the shelves inside State Bros. Markets in Ridgecrest,
California after the M 6.4 event (Source: CNN, 2019)

Figure 12. Books cover the floor at a Kern County Library in Ridgecrest after the 6.4
magnitude event (Credit: Richard Wagner, Source: KTLA, 2019)

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Figure 13. Broken bottles and other goods in a store in Lake Isabella after the magnitude
6.4 earthquake18(a)(b)
Figure 14. (a) The Daily Independent Newspaper office ceiling damaged during the M 6.4
event (Jessica Watson, AP); (b) Suspended ceiling partial failure at a laundromat in
Ridgecrest after the M 6.4 event (Photo by Terry Pierson, The Press-Enterprise/SCNG)

18 https://www.sfchronicle.com/bayarea/article/6-4-quake-hits-Mojave-Desert-felt-in-Los-Angeles-

14071924.php#photo-17804993
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17

(a)
(b)
Figure 15. (a) Fallen concrete panels at a building in North Ridgecrest (Source: Karen Hua
via Twitter); (b) Glass facade damage in retail building due to M 6.4 event (Source: AP)

Figure 16. Cracks in masonry walls in Trona following the M 7.1 event (Photo by Christine
Goulet, SCEC)
Residential Construction
At least two residential houses in Ridgecrest caught fire after the M 6.4 event most probably due
to broken gas pipes. One house on the corner of Sunland Street and East California Avenue had
the garage and part of the main roof burnt by fire (Figure 17a). Another house was heavily
damaged by fire, after the M 6.4 event (Figure 17b). Figure 18a shows a collapsed chimney andthe upper brick layers that fell from a masonry wall. A house was damaged with diagonal andvertical cracks in exterior walls (Figure18b). Other buildings with failed chimneys or damaged
walls are shown in Figures 19 to 24. Many unreinforced masonry chimney failures were observedin Trona after the M 7.1 event. Preliminary reports cite significant damage in Trona after the M
7.1, pending more information from field teams. Typical damage to timber framed homes is shownin Figure 22, while damage to items in a cafeteria named "My Enchanted Cottage" at 214 W
Ridgecrest Blvd Ridgecrest, CA 93555, are shown in Figure 25.

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18

(a)
(b)
Figure 17. Two houses caught fire in Ridgecrest after the M 6.4 event (San Bernandino Sun,2019; AP News, 2019)(a) Collapse of a chimney and upper section of a masonry wall(b) Cracks in exterior walls(c) Fire damage after M 7.1 event
Figure 18. Damage to masonry structures (Sources: (a) Reuters, 2019; (b) Yahoo, 2019, and(c) themegaagency, Instagram, 2019)

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Figure 19. A cinderblock wall partially destroyed in Ridgecrest following the magnitude 7.1
Earthquake (CNN, 2019)

Figure 20. Damage to a masonry house in Trona after the M 7.1 earthquake (Source: Eytan
Wallace via Twitter)

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20

(a)

(b)
Figure 21. Damage to a masonry houses in Trona after the M 7.1 earthquake (Sources:a)
Rob Mcmillan via Twitter, b) CBS Los Angeles)

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21

(a)
(b)
Figure 22. (a) Damaged house in Trona after the M 7.1 event (credit: Mario Tama, AFP); (b)Damaged walls of a home in Trona (Source: @23ABCNews via Twitter)

Figure 23. Collapsed cinder block walls of a masonry house (Source: Karen Hua viaTwitter)

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance22Figure 24. Broken masonry chimney and damaged masonry walls (Source: Ken O’Doll via
Twitter)

Figure 25. Contents damage in a cafeteria due to the M 6.4 event (AP News, 2019)
At least two mobile homes were damaged during the M 6.4 event. One is at Trousdale Estates at
210 W. Ward Ave. in Ridgecrest where a woman and her child were inside the building when theearthquake occurred but were unharmed, Figure 26(a). The mobile home appears to have been
displaced off its supports, resulting in damage to the skirt surrounding the trailer chassis. Anothermobile home also appears to have fallen off its supports resulting in damage to the metal columns
supporting the roof over the porch, Figure 26(b). Out of 193 mobile homes in three mobile homeparks north of Ridgecrest, eight mobile homes collapsed; none of which were tied down or had
seismic braces (Keith Porter from the field.) It appears that most of these collapses were due tothe M 7.1 event. According to Jonathan Stewart from the field: there are damaged structures inTrona, in many cases this is from the effects of ground failure. Following the M 7.1 event, Trona
seems to be largely abandoned, due to loss of water (it is served by the water pipes ruptured by

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fault rupture). Only police and utility personnel present in the area. Unlike Trona, Ridgecrest
experienced little structural damage except in especially vulnerable structures, significant content
and non-structural damage.

(a)

l
(b)
Figure 26. Damage to mobile homes in Ridgecrest area due to the M 6.4 event (a) Source:
Bakersfield News, 2019; (b) Source: Yahoo News, 2019
Schools
At the time of authoring this report, there were no available reports or articles indicating significant
damage to local schools. A Fourth of July performance was taking place at Burroughs High School
when the M 6.4 earthquake hit, which was documented in a video posted to Twitter (Figure 27,
Fox26News, 2019). Since Burroughs High School had back-up generators, they were able tokeep the air conditioning operational despite disruption of power elsewhere. Burroughs HighSchool served as a cooling center, allowing people to gather in the gymnasium and stay cool
during the day. The American Red Cross later set up an evacuation center at Burroughs High.
Ridgecrest High School similarly had individuals temporarily shelter in their gymnasium -- KCFD
reported that at least 15 patients from Ridgecrest Regional Hospital were moved there due topotential damage.

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance24Figure 27. Fourth of July performance taking place at Burroughs High School during the
M 6.4 earthquake; screen capture from video recorded by Yari Mower (AOL, 2019)
Instrumented Structures
Tables 2 and 3 report the recorded peak structural acceleration (PSA) at the instrumented
structures in descending order for the M 6.4 and M 7.1 events, respectively. Stations with PSA
greater than 0.05g are listed in the tables. The highest peak acceleration (0.29g) was recorded at
a 3-story office building at Lancaster for the M 6.4 event. The same building also recorded
significant shaking (PSA = 0.326g) during the M 7.1 event. At the time of writing this report, no
information on structural or non-structural damage was available for the above mentioned
building. Significant shaking has also been recorded for both events at Hwy 395/Brown Road
Bridge at Ridgecrest (0.27g for the M 6.4 and 0.6g for the M 7.1 events). Based on preliminary
field investigation19, no damage was visible from this field assessment after the M 6.4 event.
Interestingly, the highest peak structural acceleration for the M 7.1 event was recorded 230 km
away from the epicenter at the Port of Long Beach (1.29g). Furthermore, 10 story residentialbuilding at Burbank, situated about 180 km away from the epicenter, experienced strong shaking
during both events recording 0.22g and 0.30g for M 6.4 and M 7.1 events, respectively.

19 This field investigation was conducted on July 5th, 2019 by Prof. Farzin Zareian, UCI.

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Table 2. Peak acceleration recorded at instrumented structures during the M 6.4 event(Source: CESMD database)Station Name

Network

CodeDistance (km)

PSA (g)Lancaster - 3-story Office Bldg.

CGS

24517

127.6

0.291

Lancaster - 5-story Hospital

CGS

24609

127.6

0.275

Ridgecrest - Hwy 395/Brown Road Bridge

CGS

33742

28.6

0.274

Burbank - 10-story Residential Bldg.

CGS

24385

183.8

0.221

Palmdale - 5-story Hospital

CGS

24457

137.4

0.120

Redlands - 1-story Warehouse

CGS

23495

183.8

0.074

San Bernardino - 5-story Hospital

CGS

23634

175.4

0.063

Los Angeles - 9-story Univ Hospital Bldg.

CGS

24260

193.1

0.062

San Bernardino - 6-story Hotel

CGS

23287

183.1

0.057

Los Angeles - 7-story Hospital

CGS

24397

192.2

0.054

Los Angeles - 52-story Office Bldg.

CGS

24602

196.0

0.053

Pasadena; Millikan Library

NSMP

5407

183.0

0.052

Palmdale - Hwy 14/Barrel Springs Bridge

CGS

24706

140.6

0.050

Riverside - 6-story Hospital

CGS

13633

192.2

0.050

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Table 3. Peak acceleration recorded at instrumented structures during the M 7.1 event(Source: CESMD database)Station Name

Network

CodeDistance (km)

PSA (g)Long Beach - Port of LB Pier T

CGS

14412

230.3

1.290

Ridgecrest - Hwy 395/Brown Road Bridge

CGS

33742

22.1

0.605

Lancaster - 3-story Office Bldg.

CGS

24517

129.9

0.326

Burbank - 10-story Residential Bldg.

CGS

24385

186.7

0.300

Lancaster - Airport Control Tower

CGS

24474

126.8

0.236

Palmdale - 5-story Hospital

CGS

24457

140.2

0.143

San Bernardino - 5-story Hospital

CGS

23634

183.2

0.123

Riverside - 6-story Hospital

CGS

13633

199.7

0.119

San Bernardino - 5-story CSUSB Library

CGS

23285

177.6

0.087

Los Angeles - 8-story County Med Ofc Bld

CGS

24249

197.4

0.077

Palmdale - Hwy 14/Barrel Springs Bridge

CGS

24706

143.6

0.074

Irvine - 6-story Hospital

CGS

13439

234.4

0.071

Los Angeles - 52-story Office Bldg.

CGS

24602

199.5

0.069

Los Angeles - 7-story Hospital

CGS

24397

195.5

0.065

Los Angeles - 9-story Office Bldg.

CGS

24579

200.3

0.065

Los Angeles - 8-story CSULA Admin. Bldg.

CGS

24468

195.5

0.063

Palm Springs - 4-story Hospital

CGS

12299

235.0

0.062

Los Angeles - 19-story Office Bldg.

CGS

24643

203.4

0.054

Pasadena - 9-story Commercial Bldg.

CGS

24571

186.4

0.050

Los Angeles - 9-story Univ Hospital Bldg.

CGS

24260

196.8

0.050

Fire Following Earthquake
M 6.4 Earthquake - July 4, 2019
The M 6.4 earthquake caused two structural fires, a brush fire, and a few vegetation fires. Thissection will focus on the fires caused in structures. The structural fires occurred in Ridgecrest, CA
and in Bakersfield, CA and were reported by the Kern County Fire Department. It is unknown at
the time as to the cause of the fires, but multiple gas leaks were also reported after theearthquake. Figure 28(a) shows an active fire in Ridgecrest and Figure 28(b) shows the post-fire

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condition of the house. Figure 29 shows the Bakersfield Fire Department notification of the active
fire in Bakersfield after the M 6.4 event.

(a)(b)
Figure 28. Fire following M 6.4 event in Ridgecrest (a) active fire conditions (ABC, 2019),
and (b) post-fire condition (Source: San Bernardino Sun, 2019)

Figure 29. Fire following M 6.4 event in Bakersfield (Source: Bakersfield Fire Department
Facebook Page)
Fire departments must respond to all gas leaks with the code of “structural fire.” Therefore,
through the Kern County Fire Department (KCFD) incident reporter, these locations can be
determined. There were three reports of gas leaks in Bakersfield due to the M 6.4 event. These
are shown as structural fires and the exact locations are provided in the Earthquake Engineering
Research Institute (EERI) Virtual Earthquake Reconnaissance Team (VERT) report that isincluded in Appendix B of this report.
M 7.1 Earthquake - July 5, 2019
There were 14 structural fire responses by the KCFD within about 12 hours after the earthquake.
While all of these may not be earthquake related, these are mapped below, and exact locations
PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance28

are provided in the VERT report included in the appendix of this report. A map of the locations ofboth the M 6.4 and M 7.1 KCFD responses for structural fires are shown in maps in Figure 30
where these locations were concentrated in Bakersfield and Ridgecrest. A link to the Google Map
is provided in the VERT report included in Appendix B of this report.

(a)(b)
Figure 30. Distribution of structural fire responses by the KCFD after the two earthquakes;
purple indicates M 6.4 responses and orange indicates M 7.1 responses, (a) in Bakersfield,and (b) in Ridgecrest

Lifelines
The M 6.4 Ridgecrest earthquake generated minor damage to lifelines, including some cracks on
178 Highway, localized water breaks, and limited damage to the electric infrastructure. The
majority of the damage was quickly repaired by the responsible agencies. The areas affected bylifelines damage were the town of Trona and Ridgecrest. The M 7.1 event created more significant
damage than the M 6.4 one, generating several cracks on the SR 178 and rockslides.
Transportation Infrastructure and Bridges
A large crack has formed in a highway near Ridgecrest following the earthquake event on July 4,
2019. The road damage included a 12-inch (305 mm) crack across Highway 178, about two miles
west of Trona Road. Moreover, several cracks formed on the SR 178 between Trona andRidgecrest after the M 7.1 event. The roads have been closed for repairs and were quickly
repaired by Caltrans crews (KTLA, 2019, Figures 31 to 33). After the M 6.4 event, highways in
San Bernardino County remained open. However, after the M 7.1 event, the SR 178 between
Trona and Ridgecrest was closed for repairs. No damage to bridges and airports was reported.

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29

(a)

(b)

(c)

(d)

(e)
(f)
Figure 31. Damage reported in Highway 178 (a) Large crack formed near Trona20 (b) a
motorcyclist rides over a temporarily repaired part of the damaged highway in Ridgecrest
one day after the earthquake, demonstrating the rapid response of repair crews; (c)damage reported in Ridgecrest during the M 6.4 event21; (d) surface cracks near Ridgecrest
following the M 6.4 event22 (AP Photo/David McNew) (e) Crack length near Ridgecrest after
the July 4th event23; (f) rockslides cause closure of the highway from the M 7.1 event on
Friday night; announced clear Saturday at 1 AM by Kern Country24

20 https://ktla.com/2019/07/04/6-6-earthquake-jolts-southern-california-on-4th-of-july/
21 https://www.facebook.com/nextquake/photos/rpp.1522642377960072/2878715709019392/?type=3&theater
22 https://www.reuters.com/article/us-california-quake/big-quake-rattles-area-of-20-million-people-in-california-no-one-killed-idUSKCN1TZ1VB
23 https://www.facebook.com/USGeologicalSurvey/
24 https://www.latimes.com/local/lanow/la-me-trona-earthquake-batters-rockslides-ridgecrest-20190705-story.html
PVRR: Preliminary Virtual Reconnaissance Report
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Figure 32. A road in Trona slightly damaged during M 6.4 event (AP Photo/M. Hartman25)

(a)

(b)

(c)
(d)
Figure 33. (a) Several cracks on the SR 178 WS between Trona and Ridgecrest after the M
7.1 event. The road was closed for repairs; (b) Details of the cracks 26; (c) Other picture of
the cracks27; (d) Rockfall cleared on SR 178 between Trona and Ridgecrest but route stillclosed for temporary repair28
An assessment of the bridges instrumented for strong motion by the California Department ofTransportation. Bridge Number 50-0340 at Brown Road, Figure 34(a), was instrumented for
25 https://www.nbcnews.com/news/us-news/6-4-magnitude-earthquake-shakes-southern-california-n1026621
26 https://twitter.com/Caltrans8
27 https://heavy.com/news/2019/07/trona-earthquake-damage-photos/
28 https://heavy.com/news/2019/07/trona-earthquake-damage-photos/

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strong motion and was triggered by this earthquake, Figure 34(b). It is located about 14 miles
from the epicenter of this earthquake. The California Geological Survey (CGS) personnel
processed the data and send it to Caltrans for emergency use. Typically, a default filter of threeseconds is used to filter strong motion records, but with the long period energy associated withthis earthquake, a 10 second corner period was utilized. The ground sensors show a peakacceleration of 0.24g and the structure recorded 0.60g (refer to Figure 35). The structure
experienced long motions of 116 mm transversely and 152 mm longitudinally (refer to Figure 36).
Comparing the wave forms from the top and bottom of the column, they show that they move
together and should have no relative deflection. Thus, from this preliminary investigation, no
cracks are expected of the columns of this bridge.
A structure having a long period of natural vibration (e.g. 6 sec) such as a tall building or large
bridge (e.g. Vincent Thomas) would have experienced great motion (harmonic vibration). Since
this bridge structure of Brown Road and the local buildings have a high natural frequency ofvibration, they basically moved with the ground. If this epicenter was under a large city, many
structures would experience greater displacements. It is indeed fortunate that these two big
events occurred in a rural area.
Another interesting observation is that the free field vertical spectral acceleration (Sa) is almost
4g at 0.4 seconds (refer to Figure 37). Because of the magnitude of the two events, many groundstations, bridges, buildings and geotechnical downhole arrays were triggered and data isavailable29.

29 https://strongmotioncenter.org/cgi-bin/CESMD/iqr_dist_DM2.pl?ID=ci38457511

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32

(a)

(b)
Figure 34. Caltrans Bridge No. 50-340 of Brown Road (a) Photograph of the bridge; (b)Bridge layout and instrumentation by CSMIPPVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance33

Figure 35. Measured accelerations of Bridge No. 50-340 of Brown Road during M 7.1 event(for Channel numbers, refer to Figure 34(b))

PVRR: Preliminary Virtual Reconnaissance Report
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Figure 36. Computed displacement from measured accelerations of Bridge No. 50-340 ofBrown Road during M 7.1 event (for Channel numbers, refer to Figure 34(b))

PVRR: Preliminary Virtual Reconnaissance Report
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Figure 37. Computed 5% damped spectral accelerations from measured accelerations ofBridge No. 50-340 of Brown Road during M 7.1 event (for Channel numbers, refer to Figure34(b))
Utilities for Electricity and Water Distribution
Power was knocked out in Trona, Figure 38, a small town closest to the epicenter, located about
25 miles north of Ridgecrest. In addition, residents reported water main breaks and gas line
breaks30. It was reported that 2,000 customers in Kern County and another 3,000 in San
Bernardino and Inyo lost power after the M 7.1 event. Service had been restored quickly31. Somewater pipes were damaged during the M 6.4 event. Refer to Figures 39 and 40.

30 https://losangeles.cbslocal.com/2019/07/04/6-6m-quake-strikes-near-ridgecrest-in-kern-county/
31 https://www.washingtonpost.com/nation/2019/07/06/california-earthquake/?utm_term=.60923781a92e

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36

(a)
(b)
Figure 38. (a) A utility pole in Trona was damaged during the earthquake32; (b) Workers
repair damaged utility lines in Trona, CA (AP Photo/Mario Tama | Getty Images33(a)(b)
Figure 39. (a) Water spews from pipes in Trona damaged by the M 6.4 event (AP Photo/Matt
Hartman34; (b) A crack on Highway 178 seen during fixing a broken water line south of
Trona (Source: AP Photo/F.J. BROWN | AFP/GETTY IMAGES35

32 https://www.chron.com/bayarea/article/6-6-earthquake-southern-California-san-bernardino-

14071882.php#photo-17806022
33 https://www.mprnews.org/story/2019/07/05/strongest-earthquake-in-20-years-rattles-southern-california
34 https://www.sfchronicle.com/bayarea/article/6-4-quake-hits-Mojave-Desert-felt-in-Los-Angeles14071924.php#photo-17806048
35 https://www.wknofm.org/post/64-magnitude-earthquake-hits-southern-california-rattling-large-swathstate
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37

(a)
(b)
Figure 40. (a) Exploded water pipe reported during the M 6.4 event, consequently forminga crater near Ridgecrest (Source: AP Photo/Etienne Laurent, EPA-EFE36; (b) Crews dealing
with a water main that ruptured during the earthquake37

Non-Structural Damage
This event caused significant damage to non-structural elements such as infill walls, partition walls(usually built of masonry), ceilings and veneers and various types of building contents. In addition
to the equipment damage shown with photographs in previous sections, there was damage tosuspended ceilings, Figure 41.

Figure 41. Suspended ceiling damage at Baptist Church in Ridgecrest38

36https://www.desertsun.com/story/news/local/2019/07/04/6-6-magnitude-earthquake-rattles-parts-

southern-california/1650319001/
37 https://www.msn.com/en-us/weather/weathertopstories/64-magnitude-earthquake-hits-southerncalifornia/ss-AADRIAr?ocid=msn360#image=16
38 http://www.bpnews.net/53239/calif-quakes-prompt-southern-baptist-response
PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance38

Geotechnical Failures
M6.4 Earthquake - July 4, 2019
The M 6.4 earthquake caused geotechnical damage in the form of surface fault rupture, groundseparation, and ground fissures. An approximately 12” wide crack was formed across Trona Road
about 2.5 miles South of State Route 178 (see VERT report included in Appendix B). Anotherlarge crack was formed across State Route 178 about 2 miles West of Trona Road. Several othercracks along State Route 178 were reported by the Caltrans District 8 Twitter page; according to
the same source these cracks were repaired by the Caltrans District 9 Maintenance crews within
an hour after the event. According to the USnews, California Highway Patrol announced that
overpasses and underpasses were not damaged and these cracks were primarily in the county
roads.
Several traces of fault rupture and ground fissure were also reported near Ridgecrest after theearthquake. Satellite images reflected subtle left-lateral fault rupture after the M 6.4 Ridgecrest
earthquake.

(a)
(b)
(c)
Figure 42. Geotechnical damage following M6.4 Ridgecrest (a) 12” wide crack across Tronaroad39, (b) Caltrans District 9 Maintenance crews make repairs to cracks along SR 178 near
Trona (Source: Caltrans District 8 Twitter page40), and (c) ground separation and offset(photo by Emily Guerin41). All images reported in the VERT report, Appendix B.

39 https://heavy.com/news/2019/07/california-earthquake-today-map-damage-magnitude/
40
41

https://twitter.com/Caltrans8
https://twitter.com/guerinemily
PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance39

Figure 43. 100 ft (30.48 m) wide zone of parallel ruptures showing left lateral (LL) and somedilation along the Ridgecrest surface rupture reported by Danielle Verdugo Madugo42

(a)
(b)
(c)
Figure 44. Surface Fault Rupture following M 6.4 Ridgecrest earthquake (a) Off the roadrupture (reported by Emily Guerin43), (b) Ground crack near Ridgecrest44, (c) fault rupture
across Randsburg Wash Road to the south of State Route 178, measured offset of
approximately 1.5 feet (457 mm) (Source: Brian Olson Twitter page45). All images reported
in the VERT report, Appendix B.

42 https://twitter.com/DanielleVerdugo
43

https://twitter.com/guerinemily

44 https://www.newsweek.com/california-earthquake-viral-videos-panic-chaos-tremor-aftershock-1447699
45 https://twitter.com/mrbrianolson

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40

(a)
Figure 45. (a) Lateral displacement of 100 cm; and (b) Wide distributed shears46(b)

M7.1 Earthquake - July 5, 2019
The M 7.1 earthquake caused geotechnical damage in the form of surface fault rupture (e.g.
offset, ground fissures etc.), rockfalls, and liquefaction-induced failures (e.g. lateral spreading).
A North-West trending fault rupture measured up to 6 feet (229 mm) of right-lateral offset on the
China Lake NWAS base47. A right-lateral offset of about 6.5 feet (248 mm) and a vertical offset ofabout 3 feet (114 mm) were reported48. A surface rupture across State Route 178 caused a rightlateral offset, likely related to the North-West trending conjugate fault49, photo taken from the
VERT report, Appendix B. Fault rupture also bended railroad tracks and caused damage to the
nearby road; a 3-feet (114 mm) right lateral offset was reported50.

46 https://twitter.com/ChupikColin/status/1147558794148245504
47 https://twitter.com/mrbrianolson
48 https://twitter.com/mrbrianolson
49 https://twitter.com/mrbrianolson
50 https://twitter.com/neotectonic

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance41

Figure 46. (a) Aerial view of the faulted road on the China Lake NWAS base, about 6.5 feet
(248 mm) right lateral (RL) and 3 feet (114 mm) vertical offset51, (b) North-West trending
fault rupture measuring 6 feet (229 mm) of right-lateral offset on the China Lake NWAS
base52, and (c) Bent railroad track due to the fault rupture , close to 3 feet (114 mm) of RL
offset53
Multiple ground cracks along State Route 178 near Post Mile 8.5 were patched before opening
the road to traffic (the duration of closure is now known at this time). According to the CaltransDistrict 8 Twitter page, Caltrans started permanent construction repairs on State Route 178
approximately six miles east of Ridgecrest. The repairs were done in three separate areas withinfour mile stretch along the State Route 178. All bridges and highway structures have been
evaluated by Caltrans engineers and they have been determined safe for normal operations 54.

51 https://twitter.com/mrbrianolson
52 https://twitter.com/mrbrianolson
53 https://twitter.com/neotectonic
54 https://twitter.com/Caltrans8

PVRR: Preliminary Virtual Reconnaissance Report
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Figure 47. Aerial views of ground failure indicating left-stepping and right-stepping lateral
faults reported by Ian Pierce55

Figure 48. Multiple ground cracks along SR 178 (Source: Caltrans8 Twitter page56, takenfrom the VERT report, Appendix B)

55 https://twitter.com/neotectonic
56 https://twitter.com/Caltrans8

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance43

Figure 49. SR 178 near PM (post mile mark) 8.5 Caltrans crews making repairs to patchroad before open to traffic57 (picture taken 12:53am 07/06/2019)
Rockfall caused road closure in State Route 178 between Bakersfield and Lake Isabella. Thisroad was later opened to traffic. Rockfall in State Route 178 between Trona and Ridgecrest
caused traffic closure; the rockfall was later cleared. Rockfall was also reported from State Route
190 Townes Pass and State Route 127 near the Tecopas Hot Springs turnoff58.

Figure 50. Rockfall damages in Ridgecrest59 (left) and Trona60 (right). All images reported
in the VERT report, Appendix B.
Significant geotechnical damage in Trona resulted from at depth liquefaction (Ken Hudson,
personal communication) leading to lateral spreading at the surface. Few sand boils were also
observed. Photos below were collected by EERI members performing field investigation after the
57 https://twitter.com/Caltrans858 https://twitter.com/Caltrans859

https://twitter.com/neotectonic

60 https://www.latimes.com/local/lanow/la-me-trona-earthquake-batters-rockslides-ridgecres

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Building R esilience through Reconnaissance44M7.1 earthquake and shared by Kenneth Hudson (one of the EERI team members). The
groundwater table in this area is reported to be fairly shallow (~1.5 ft (247 mm) according to
http://wdl.water.ca.gov/waterdatalibrary/ and nearby well data). The combination of heavy rainfall
during the past winter with the lakebed could justify these observations as well as the occurrenceof liquefaction (Ken Hudson, personal communication).

Figure 51. Liquefaction induced lateral spreading and sand boils causing damage to theroadway, and infrastructure in the Trona area (source for all: courtesy of Kenneth Hudson,one of EERI field investigation team members) [clockwise from top left: Esparza restaurantcommercial building distance from – closest distance to Searles Lake 0.6 mile; US Post
Office Building – closest distance to Searles Lake 1.0 mile; corner of California Street andArgus Avenue; Shell gas station – closest distance to Searles Lake 1.0 mile].

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Figure 52. Closer look at ground failure observed at underground storage tank at Shell gas
station on Trona Road (Source: courtesy of Kenneth Hudson, one of EERI field
investigation team members).

Current Conditions, Access Restrictions and Recommendations
There have been access restrictions to some hospitals. The Ridgecrest Regional Hospital has
now reopened after being closed for a few days after both earthquake events61. As of this report,
the authors are not aware of any unusual access restrictions in place.
Recommendations for further investigation may include the following:
1. Effect of the accumulated damage from the M 6.4 earthquake on the response during
the M 7.1 earthquake,
2. Evaluation of the accuracy of regional scale simulations (those of NHERI SimCenter and
X. Lu Tsinghua group) by comparing their results against the observed damage,
3. Investigation of the current status of ShakeAlertLA. Does it require revisions, change ofthresholds, etc.?
4. Current status of earthquake insurance in California,
5. Reasons behind the relatively poor performance of the water supply network despite theongoing efforts for its improvement around the Los Angeles area, and6. Further investigation of performance of non-structural components including mobile
homes.

61 https://twitter.com/FlavioLacayo/status/1148011491984998400?s=20

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StEER Response Strategy
Based on prior event experience and preferences, StEER volunteers are generally offeredpositions on two types of StEER Teams:●

Virtual Assessment Structural Teams (VASTs) were formed to assemble data on theevent from public sources and lead authorship of two reports: The Preliminary Virtual
Assessment Structural Team (P-VAST) Report and The Early Access Reconnaissance
Report (EARR) based on the data from FAST-1. VASTs also work to enrich FAST datawith other information gleaned from inventory and high-resolution imagery and participate
in quality assurance and data cataloging processes.

●

Field Assessment Structural Teams (FASTs) were formed by invitations to individuals
with prior field experience and expertise relevant to this type of event. FASTs were used
to rapidly gather essential data only visible on the ground, with the understanding thatthese will be enriched with additional sources of data through aligned StEER efforts.

Given the magnitude of the two Ridgecrest earthquakes, StEER deployed the VAST who
produced this report. However, the observed limited structural damage discussed in this report
does not warrant the need to deploy a FAST at this stage. StEER will continue to monitor thesituation and work with local field reconnaissance teams in case the situation changes andnecessitates deploring a FAST. In this case a FAST drawn from regional expertise with priorearthquake reconnaissance experience will be sought. Typically, a FAST will gather samples ofdamage to buildings and other infrastructure using a combination of door-to-door (D2D) damage
assessments, unmanned aerial surveys (UASs) and StreetView imagery. VAST will review
damage reports and data from FAST as swiftly as possible, as well as other public data from thisevent, as conducted in this report. This will be used to generate an Early Action Reconnaissance
Report (EARR) to be released on DesignSafe. The findings of FAST will then inform subsequent
FASTs that may deploy to the affected regions.

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Appendix A: Expected Earthquake Performance of
Buildings Designed to the California Building Code62

62 Brochure developed by Grace Kang of PEER and several co-authors of this report for the CSSC.

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50

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Appendix B: EERI VERT Report

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References
The following sources were consulted in the authorship of this report:
Abrahamson, N. A., Silva, W. J., and Kamai, R. (2014). Summary of the ASK14 Ground Motion
Relations for Active Crustal Regions. Earthquake Spectra, 30(3), 1025-1055.
doi:10.1193/070913eqs198m
Baker, J. W., and Cornell, C. A. (2008). Vector-valued Intensity Measures Incorporating Spectral
Shape For Prediction of Structural Response. Journal of Earthquake Engineering, 12(4), 534554. doi:10.1080/13632460701673076
Bureau, C. (2018). American Community Survey 2013-2017 5-year Data Release. Retrieved
from https://www.census.gov/newsroom/press-kits/2018/acs-5year.html
David M. Boore and Gail M. Atkinson (2008) Ground-Motion Prediction Equations for the
Average Horizontal Component of PGA, PGV, and 5%-Damped PSA at Spectral Periods
between 0.01 s and 10.0 s. Earthquake Spectra: February 2008, Vol. 24, No. 1, pp. 99-138.
Ross S. Stein, Tiegan Hobbs, Chris Rollins, Geoffrey Ely, Volkan Sevilgen, and Shinji Toda,(2019), Magnitude 7.1 earthquake rips northwest from the M 6.4 just 34 hours later, Temblor,
http://doi.org/10.32858/temblor.037
USGS (2019a), Latest Earthquakes M 6.4 - 12km SW of Searles Valley, CA, Last accessed July
7, 2019. https://earthquake.usgs.gov/earthquakes/eventpage/ci38443183/executive
USGS (2019b), Latest Earthquakes M 7.1 - 17km NNE of Ridgecrest, CA, Last accessed July 7,
2019. https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/executive

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance70Acknowledgements
StEER gratefully acknowledges the financial support of the National Science Foundation underAward CMMI-1841667, with deep appreciation for the mentorship provided by Dr. Joy Pauschke.
Any opinions, findings, and conclusions or recommendations expressed in this material are thoseof the authors and do not necessarily reflect the views of the National Science Foundation.
StEER team appreciates the collaboration with the Earthquake Engineering Research Institute(EERI) and its Virtual Earthquake Reconnaissance Team (VERT). We thank Professor X. Lu,
Tsinghua University, and his research group for the technical assistance on the response spectra
shown in Figure 5 of this report. We also thank Professors J. Stewart, UCLA, and his GEER teamand F. Zareian, UCI, for sharing their first-hand preliminary field observations.
The discussion about the performance of Bridge Number 50-0340 instrumented by CGS has beenshared by Mr. Pat Hibley, Office of Earthquake Engineering, Caltrans. The authors acknowledge
Mr. Hibley for his contributions of this discussion and also of Figures 34 to 37.
The sharing of videos, damage reports and briefings via DesignSafe-CI’s Slack channel was
tremendously helpful and much appreciated. These collaborations and exchanges of critical datain the landfall stages benefited greatly from the work of the DesignSafe CI team who continuously
supported and responded to StEER’s emerging needs.

PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance71About StEERThe National Science Foundation (NSF) awarded a 2-year EAGER grant (CMMI 1841667) to a
consortium of universities to form the Structural Extreme Events Reconnaissance (StEER)
Network. StEER’s mission is to deepen the structural natural hazards engineering (NHE)community’s capacity for reliable post-event reconnaissance by: (1) promoting community-driven
standards, best practices, and training for RAPID field work; (2) coordinating official event
responses in collaboration with other stakeholders and reconnaissance groups; and (3)representing structural engineering within the wider extreme events reconnaissance (EER)
consortium in geotechnical engineering (GEER) and social sciences (SSEER) to foster greater
potentials for truly interdisciplinary reconnaissance. StEER also works closely with the NSFsupported Natural Hazards Engineering Research Infrastructure (NHERI) RAPID facility andcyberinfrastructure Reconnaissance Portal to more effectively leverage these resources to benefit
StEER missions.
StEER relies upon the engagement of the broad NHE community, including creating institutional
linkages with dedicated liaisons to existing post-event communities and partnerships with otherkey stakeholders. While the network currently consists of the three primary nodes located at the
University of Notre Dame (Coordinating Node), University of Florida (Atlantic/Gulf Regional
Node), and University of California, Berkeley (Pacific Regional Node), StEER aspires to build a
network of regional nodes worldwide to enable swift and high quality responses to major disasters
globally.
StEER’s founding organizational structure includes a governance layer comprised of coreleadership with Associate Directors for the two primary hazards as well as cross-cutting areas ofAssessment Technologies and Data Standards, led by the following individuals:● Tracy Kijewski-Correa (PI), University of Notre Dame, serves as StEER Director
responsible with overseeing the design and operationalization of the network.
● Khalid Mosalam (co-PI), University of California, Berkeley, serves as StEER
Associate Director for Seismic Hazards, leading StEER’s Pacific Regional node andserving as primary liaison to the Earthquake Engineering community.
● David O. Prevatt (co-PI), University of Florida, serves as StEER Associate Director
for Wind Hazards, leading StEER’s Atlantic/Gulf Regional node and serving as primaryliaison to the Wind Engineering community.
● Ian Robertson (co-PI), University of Hawai’i at Manoa, serves as StEER Associate
Director for Assessment Technologies, guiding StEER’s development of a robust
approach to damage assessment across the hazards.
● David Roueche (co-PI), Auburn University, serves as StEER Associate Director for
Data Standards, ensuring StEER processes deliver reliable and standardized
reconnaissance data.

StEER’s response to the 2019 Ridgecrest Earthquakes preceded the formation of its official
policies, protocols and membership, which are still in active development. All policies,
procedures and protocols described in this report should be considered preliminary and will be
refined with community input as part of StEER’s operationalization in 2019.

StEER Event Report Library
PVRR: Preliminary Virtual Reconnaissance Report
Building R esilience through Reconnaissance72Lu, X. Gunay, S. Kijewski-Correa, T. Robertson, I. Mosalam, K. Prevatt, D. Roueche, D.(201906-22) “StEER - 17 June, 2019 Yibin City, Sichuan, China Earthquake: Event Briefing.”
DesignSafe-CI. https://doi.org/10.17603/ds2-2117-1565.
Sutley, E. Lequesne, R. Li, J. Kirkham, W. Chen, Z. Al-Sabawy, A. Daniel, L. Enderami, S. Kim,
J. Mudaliar, T. Taher, S. Sharma, P. Roueche, D. (2019-06-12) “StEER - 28 MAY 2019
LINWOOD, KS EF4 TORNADO: FIELD ASSESSMENT STRUCTURAL TEAM (FAST) EARLYACCESS RECONNAISSANCE REPORT (EARR).” DesignSafe-CI. https://doi.org/10.17603/ds2xz1j-nm14.
Yan, G. Zhang, X. Elgawady, M. Han, D. Li, T. Li, Z. Zhao, Y. Honerkamp, R. Zhao, J. Ramadan,
A. Esswein, E. Barner, T. Roueche, D. (2019-06-11) “StEER - 22 May 2019 JEFFERSON CITY,
MO TORNADO: FIELD ASSESSMENT STRUCTURAL TEAM 1 (FAST-1) EARLY ACCESSRECONNAISSANCE REPORT (EARR).” DesignSafe-CI. https://doi.org/10.17603/ds2-qa2bwz63.
Miranda, E., Acosta, A., Ceferino, L., Davalos, H., Galvis, F., Gunay, S., Heresi, P., Macedo, J.,
Miranda, S., Ramos, J., Rojas, P., Ruiz-Garcia, J., Vera, X., Mosalam, K., Robertson, I., Roueche,D., (2019-06-04) “StEER - 26 MAY 2019 LAGUNA PERU EARTHQUAKE: PRELIMINARYVIRTUAL ASSESSMENT STRUCTURAL TEAM (P-VAST) REPORT.” DesignSafe-CI.
https://doi.org/10.17603/ds2-cbff-4878.
Gunay, S. Mosalam, K. Kijewski-Correa, T. Prevatt, D. Robertson, I. Roueche, D. (2019-06-04)“StEER - 22/23 April, 2019 Philippines Earthquakes: Event Briefing.” DesignSafe-CI.
https://doi.org/10.17603/ds2-6my9-yz67.
Roueche, D., Cleary, J., Barnes, R., Davis, B., Marshall, J., Rittelmeyer, B., Smallegan, S., Guo,
Y., Hodges, C., Kijewski-Correa, T., Salman, A., Turner, K., Merschman, E., mulchandani, H.,
Prevatt, D., Robertson, I., Mosalam, K., (2019-06-04) “StEER - 3 March 2019 Tornadoes in theSoutheastern US: Field Assessment Structural Team (FAST) Early Access Reconnaissance
Report (EARR).” DesignSafe-CI. https://doi.org/10.17603/ds2-qav0-t570.
Roueche, David; Davis, Brett; Hodges, Courtney; Rittelmeyer, Brandon; Turner, Kelly; KijewskiCorrea, Tracy; Prevatt, David; Robertson, Ian; Mosalam, Khalid (2019-01-30) , "StEER - 19
JANUARY 2019 TORNADOES IN THE SOUTHEASTERN US: FIELD ASSESSMENT TEAMEARLY ACCESS RECONNAISSANCE REPORT (EARR)”, DesignSafe-CI [publisher], Dataset,
doi:10.17603/ds2-eb6e-tr31 [DOI: https://doi.org/10.17603/ds2-eb6e-tr31]
Robertson, Ian; Esteban, Miguel; Stolle, Jacob; Takabatake, Tomoyuki; mulchandani, Harish;
Kijewski-Correa, Tracy; Prevatt, David; Roueche, David; Mosalam, Khalid (2019-01-15), "StEER- PALU EARTHQUAKE AND TSUNAMI, SULAWESI, INDONESIA: FIELD ASSESSMENT TEAM
1 (FAT-1) EARLY ACCESS RECONNAISSANCE REPORT (EARR)”, DesignSafe-CI [publisher],
Dataset, doi:10.17603/DS2JD7T [DOI: https://doi.org/10.17603/DS2JD7T]
Robertson, Ian; Head, Monique; Roueche, David; Wibowo, Hartanto; Kijewski-Correa, Tracy;
Mosalam, Khalid; Prevatt, David (2018-12-31), "StEER - SUNDA STRAIT TSUNAMI(INDONESIA): PRELIMINARY VIRTUAL ASSESSMENT TEAM (P-VAT) REPORT” DesignSafeCI [publisher], Dataset, doi:10.17603/DS2Q98T [DOI: https://doi.org/10.17603/DS2Q98T]
Mosalam, Khalid; Kijewski-Correa, Tracy; Hassan, Wael; Archbold, Jorge; Marshall, Justin;
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Mavroeidis, George; Muin, Sifat; mulchandani, Harish; Peng, Han; Pretell Ductram, AnthonyRenmin; Prevatt, David; Robertson, Ian; Roueche, David (2018-12-06), "StEER - EERI ALASKA
EARTHQUAKE: PRELIMINARY VIRTUAL ASSESSMENT TEAM (P-VAT) JOINT REPORT”
DesignSafe-CI[publisher],
Dataset,doi:10.17603/DS2MQ38[DOI:
https://doi.org/10.17603/DS2MQ38]
Roueche, David; Cleary, John; Gurley, Kurtis; Marshall, Justin; Pinelli, Jean-Paul; Prevatt, David;
Smith, Daniel; Alipour, Alice; Angeles, Karen; Davis, Brett; Gonzalez, Camila; Lenjani, Ali;
mulchandani, Harish; Musetich, Matthew; Salman, Abdullahi; Kijewski-Correa, Tracy; Robertson,
Ian; Mosalam, Khalid, (2018-10-25), "StEER - HURRICANE MICHAEL: FIELD ASSESSMENTTEAM 1 (FAT-1) EARLY ACCESS RECONNAISSANCE REPORT (EARR)" , DesignSafe-CI[publisher],
Dataset,doi:10.17603/DS2G41M[DOI:
https://ezid.cdlib.org/id/doi:10.17603/DS2G41M]
Alipour, Alice; Aly, Aly Mousaad; Davis, Brett; Gutierrez Soto, Mariantonieta; Kijewski-Correa,
Tracy; Lenjani, Ali; Lichty, Benjamin; Miner, Nathan; Roueche, David; Salman, Abdullahi; Smith,Daniel; Sutley, Elaina; Mosalam, Khalid; Prevatt, David; Robertson, Ian, (2018-10-19), "STEER HURRICANE MICHAEL: PRELIMINARY VIRTUAL ASSESSMENT TEAM (P-VAT) REPORT" ,DesignSafe-CI[publisher],
Dataset,doi:10.17603/DS2RH71[DOI:
https://ezid.cdlib.org/id/doi:10.17603/DS2RH71]
Hu, Fan; Robertson, Ian; Mosalam, Khalid; Gunay, Selim; Kijewski-Correa, Tracy; Peng, Han;
Prevatt, David; Cohen, Jade, (2018-10-11), "StEER - 2018 HAITI EARTHQUAKE: PRELIMINARYVIRTUAL ASSESSMENT TEAM (P-VAT) REPORT" , DesignSafe-CI [publisher], Dataset,
doi:10.17603/DS2Z69H [DOI: https://ezid.cdlib.org/id/doi:10.17603/DS2Z69H]
Robertson, Ian; Kijewski-Correa, Tracy; Roueche, David; Prevatt, David, (2018-10-04), “PALU
EARTHQUAKE AND TSUNAMI, SUWALESI, INDONESIA PRELIMINARY VIRTUAL
ASSESSMENT TEAM (PVAT) REPORT” , DesignSafe-CI [publisher], Dataset,
doi:10.17603/DS2XD5S [DOI: https://ezid.cdlib.org/id/doi:10.17603/DS2XD5S]
Barnes, Robert; Lytle, Blake; Rogers, Spencer; Pei, Weichiang; Kijewski-Correa, Tracy;
Gonzalez, Camila; u, Fan; Musetich, Matthew; Peng, Han; Prevatt, David; Roueche, David;
Salman,Abdullahi; Mosalam, Khalid; Robertson, Ian, (2018-09-25), "HURRICANE FLORENCE:
FIELD ASSESSMENT TEAM 1 (FAT-1) EARLY ACCESS RECONNAISSANCE REPORT(EARR)",
DesignSafe-CI[publisher],
Dataset,doi:10.17603/DS2TT3G[DOI:
https://ezid.cdlib.org/id/doi:10.17603/DS2TT3G]

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