
From temblor
January 13, 2020
Alka Tripathy-Lang
@DrAlkaTrip
Urbanization obscures a complex fault zone on which downtown San Diego sits, but decades-old geotechnical studies reveal the faults.

Urbanization in downtown San Diego. Credit: Tony Webster CC-BY-2.0.
Fault studies often rely on surface expressions of the ground’s movement. In densely populated urban areas, such as San Diego, this evidence is concealed beneath the cityscape. Now, though, a team has used historical reports to trace faults through downtown San Diego in unprecedented detail, establishing a template that other fault-prone cities can follow to illuminate otherwise hidden hazards.
Urbanization obscures geology
Downtown San Diego, popular for its beaches and parks, also hosts the active Rose Canyon Fault Zone, a complex hazard that underlies the city from northwest of La Jolla through downtown, before curving into San Diego Bay.

Rose Canyon Fault. https://www.nbcsandiego.com/
Like the nearby San Andreas, the Rose Canyon Fault is right-lateral, meaning if you were to stand on one side, the opposite side would appear to move to your right. But it plods along at a rate of 1-2 millimeters per year, unlike its speedy neighbor, which indicates a comparatively lower seismic risk.
“We haven’t had a major rupture” on the Rose Canyon Fault since people have been living atop it, says Jillian Maloney, a geophysicist at San Diego State University and co-author of the new study. So it’s hard to say what kind of damage would be caused, she says. “But, a magnitude-6.9 [of which this fault is capable] is big.”
Because of urbanization, though, “there haven’t been any comprehensive geologic investigations” of the faults underlying downtown San Diego, Maloney says. This presents a problem because detailed knowledge of active and inactive fault locations, especially in a complicated area where the fault zone bends, is key for successful seismic hazard assessments, she says. The state and federal government maintain fault maps and databases, but their accuracy at the small scale was unknown.

Map of the Rose Canyon Fault near San Diego, California, USA. USGS
Faded pages
A solution to the lack of detailed fault mapping in downtown San Diego resided in decades of old geotechnical reports. These individual studies the size of a city block or smaller are required by the city for any proposed development near active faults, as mapped by the state. Although the data are public once the reports are filed with the city, the reports had not been integrated into a comprehensive or digital resource, and the city does not maintain a list of such reports.

This bird’s-eye view of downtown San Diego was drawn by Eli Glover in 1876. Prior to the development of downtown San Diego, the Rose Canyon Fault Zone was expressed on the surface and could be seen laterally offsetting topographic features. Credit: Library of Congress, Geography and Map Division.
According to Luke Weidman, lead author of this study, which was his master’s project, the first challenge was determining how many reports were even available. Weidman, currently a geologist at geotech firm Geocon, went straight to the source: He asked several of San Diego’s large geotechnical firms for their old publicly available reports in exchange for digitizing them.
Weidman scrutinized more than 400 reports he received, dating from 1979 to 2016. Many were uninterpretable because of faded or illegible pages. He assembled the 268 most legible ones into a fault map and database of downtown San Diego. Because reports lacked geographical coordinates, Weidman resorted to property boundaries, building locations, park benches and even trees to locate the reports on a modern map, says Maloney, one of his master’s advisors. Weidman, Maloney and geologist Tom Rockwell also of San Diego State published the findings from their comprehensive interactive digital map last month in Geosphere, along with an analysis of the Rose Canyon Fault Zone in downtown San Diego.
Below from https://pubs.geoscienceworld.org/

Map of the Rose Canyon fault zone (RCFZ) through San Diego (SD), California (USA) and across the San Diego Bay pull-apart basin. Black box shows the extent of Figure 3. Grid shows population count per grid cell (∼1 km2) (source: LandScan 2017, Oak Ridge National Laboratory, UT-Battelle, LLC, https://landscan.ornl.gov/). DF—Descanso fault; SBF—Spanish Bight fault; CF—Coronado fault; SSF—Silver Strand fault; LNFZ—La Nacion fault zone.

Street map of greater downtown San Diego region showing Alquist-Priolo (AP) zones and faults from the U.S. Geological Survey (USGS) fault database (USGS-CGS, 2006). Black box shows the extent of Figures 6, 7, and 8. Background imagery: ESRI, HERE (https://www.here.com/strategic-partners/esri), Garmin, OpenStreetMap contributors, and the GIS community.
Fault findings
The team found that downtown San Diego’s active faults—defined in their paper as having ruptured within the past 11,500 years—largely track the state’s active fault maps. However, at the scale of the one-block investigations, they found several faults mapped in the wrong location, and cases of no fault where one was expected. Further, the team uncovered three active faults that were not included in the state or federal maps. At the scale at which geotechnical firms, government, owners and developers need to know active fault locations, the use of this type of data is important, says Diane Murbach, an engineering geologist at Murbach Geotech who was not involved in this study.

This map of downtown San Diego, Calif., shows fault locations as mapped by the U.S. Geological Survey (USGS), and faults as located by the individual geotechnical reports compiled in the new study. Green, light orange, dark orange and red boxes indicate whether individual geotechnical studies found no hazard (green), active faults (red) or potential fault hazards (dark or light orange). Note that the Rose Canyon Fault Zone as mapped by USGS occasionally intersects green boxes, indicating the fault may be mislocated. Where the fault is active, mismatches exist as well. Note the arrow pointing to the ‘USGS-Geotech fault difference,’ highlighting a significant discrepancy in where the fault was previously mapped, versus where it lies. Credit: Weidman et al., [2019].
Maloney says they also found other faults that haven’t ruptured in the last 11,500 years. This is important, she says, because “you could have a scenario where an active zone ruptures and propagates to [one] that was previously considered inactive.”
This research “is the first of its kind that I know of that takes all these different reports from different scales with no set format, and fits them into one [usable] database,” says Nicolas Barth, a geologist at the University of California, Riverside who was not part of this study. Many cities have been built on active faults, obscuring hints of past seismicity, he notes. “This is a nice template for others to use,” he says, “not just in California, but globally.”
References
Weidman, L., Maloney, J.M., and Rockwell, T.K. (2019). Geotechnical data synthesis for GIS-based analysis of fault zone geometry and hazard in an urban environment. Geosphere, v.15, 1999-2017. doi:10.1130/GES02098.1
See the full article here .

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Earthquake Alert


Earthquake Alert
Earthquake Network project
Earthquake Network is a research project which aims at developing and maintaining a crowdsourced smartphone-based earthquake warning system at a global level. Smartphones made available by the population are used to detect the earthquake waves using the on-board accelerometers. When an earthquake is detected, an earthquake warning is issued in order to alert the population not yet reached by the damaging waves of the earthquake.
The project started on January 1, 2013 with the release of the homonymous Android application Earthquake Network. The author of the research project and developer of the smartphone application is Francesco Finazzi of the University of Bergamo, Italy.
Get the app in the Google Play store.

Smartphone network spatial distribution (green and red dots) on December 4, 2015
Meet The Quake-Catcher Network

Quake-Catcher Network
The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.
After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).
The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).
The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).
There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.
Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.
USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.
If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.
BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.
Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.
Below, the QCN Quake Catcher Network map

ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States

The U. S. Geological Survey (USGS) along with a coalition of State and university partners is developing and testing an earthquake early warning (EEW) system called ShakeAlert for the west coast of the United States. Long term funding must be secured before the system can begin sending general public notifications, however, some limited pilot projects are active and more are being developed. The USGS has set the goal of beginning limited public notifications in 2018.
Watch a video describing how ShakeAlert works in English or Spanish.
The primary project partners include:
United States Geological Survey
California Governor’s Office of Emergency Services (CalOES)
California Geological Survey
California Institute of Technology
University of California Berkeley
University of Washington
University of Oregon
Gordon and Betty Moore Foundation
The Earthquake Threat
Earthquakes pose a national challenge because more than 143 million Americans live in areas of significant seismic risk across 39 states. Most of our Nation’s earthquake risk is concentrated on the West Coast of the United States. The Federal Emergency Management Agency (FEMA) has estimated the average annualized loss from earthquakes, nationwide, to be $5.3 billion, with 77 percent of that figure ($4.1 billion) coming from California, Washington, and Oregon, and 66 percent ($3.5 billion) from California alone. In the next 30 years, California has a 99.7 percent chance of a magnitude 6.7 or larger earthquake and the Pacific Northwest has a 10 percent chance of a magnitude 8 to 9 megathrust earthquake on the Cascadia subduction zone.
Part of the Solution
Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of the ShakeAlert system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage.
Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds. ShakeAlert can give enough time to slow trains and taxiing planes, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or chemicals in work environments and to take cover under a desk, or to automatically shut down and isolate industrial systems. Taking such actions before shaking starts can reduce damage and casualties during an earthquake. It can also prevent cascading failures in the aftermath of an event. For example, isolating utilities before shaking starts can reduce the number of fire initiations.
System Goal
The USGS will issue public warnings of potentially damaging earthquakes and provide warning parameter data to government agencies and private users on a region-by-region basis, as soon as the ShakeAlert system, its products, and its parametric data meet minimum quality and reliability standards in those geographic regions. The USGS has set the goal of beginning limited public notifications in 2018. Product availability will expand geographically via ANSS regional seismic networks, such that ShakeAlert products and warnings become available for all regions with dense seismic instrumentation.
Current Status
The West Coast ShakeAlert system is being developed by expanding and upgrading the infrastructure of regional seismic networks that are part of the Advanced National Seismic System (ANSS); the California Integrated Seismic Network (CISN) is made up of the Southern California Seismic Network, SCSN) and the Northern California Seismic System, NCSS and the Pacific Northwest Seismic Network (PNSN). This enables the USGS and ANSS to leverage their substantial investment in sensor networks, data telemetry systems, data processing centers, and software for earthquake monitoring activities residing in these network centers. The ShakeAlert system has been sending live alerts to “beta” users in California since January of 2012 and in the Pacific Northwest since February of 2015.
In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert early warning test system in California joined by Oregon and Washington in April 2017. This West Coast-wide “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost.
This next-generation system will not yet support public warnings but does allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert notifications in areas with sufficient sensor coverage.
Authorities
The USGS will develop and operate the ShakeAlert system, and issue public notifications under collaborative authorities with FEMA, as part of the National Earthquake Hazard Reduction Program, as enacted by the Earthquake Hazards Reduction Act of 1977, 42 U.S.C. §§ 7704 SEC. 2.
For More Information
Robert de Groot, ShakeAlert National Coordinator for Communication, Education, and Outreach
rdegroot@usgs.gov
626-583-7225
Learn more about EEW Research
ShakeAlert Fact Sheet
ShakeAlert Implementation Plan
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