From Temblor: “The San Andreas’ sister faults in Northern California”



May 23, 2017
David Jacobson

Check your hazard rank

The city of Ukiah, in Northern California sits right next to the Maacama Fault, which is capable of M=7.5 earthquakes and poses a significant threat to the region. (Photo from: Trulia)

In California, when most people think about faults, their thoughts are immediately drawn to the San Andreas, and to a lesser extent, the Hayward Fault. However, in Northern California, there is almost no seismicity on the San Andreas. Instead, the majority of the earthquakes occur on faults that are parallel to and east of the San Andreas. These faults are part of the greater San Andreas system, and are capable of generating large magnitude earthquakes. Today, we thought we’d take a look at two of them.

The Maacama and Bartlett Spring faults lie approximately 50 km and 80 km east of the San Andreas respectively. All of these faults are members of the greater transform boundary between the Pacific and North American plates, a margin primarily composed of nearly pure right-lateral strike-slip faults. Both the Maacama and Bartlett Springs faults are known to be active based on seismicity and creep. Creep implies there is very slow, relatively continuous motion on a fault due to tectonic deformation. While faults that creep tend to not rupture in large earthquakes, the Hayward Fault running through the San Francisco East Bay creeps and has ruptured in M=7+ quakes. So, it is not a black and white rule.

This Temblor map shows the major faults in Northern California. What is evident from this map is that the San Andreas shows almost no seismicity, which the Maacama and Bartlett Springs faults shows significant activity. It should be pointed out that the cluster of earthquakes south of Clear Lake are hydrothermally induced.

What is evident from the Temblor map above is that within the last month, there has been microseismicity along both the Maacama and Bartlett Springs faults. By examining the USGS database, it was determined that the seismicity in the last month is relatively consistent with previous months. While almost none of these quakes were felt, they highlight an obvious difference with the San Andreas. In the last month, there have been no M=1+ earthquakes on the northern San Andreas Fault. In fact, the portion of the San Andreas that ruptured in the 1906 earthquake (From San Juan Bautista to the Mendocino Triple Junction) shows almost no signs of seismic activity. What this shows that if we only used seismicity to identify faults, we would miss the greatest threat Northern California faces.

While the San Andreas may be capable of producing larger earthquakes than either the Maacama or Bartlett Spring faults, quakes on both of these could be very damaging. Based on their relative lengths, M=7.5 earthquakes are possible on either the Maacama or Bartlett Springs faults. Such quake could be devastating to the city of Ukiah, which sits right on the Maacama Fault. Based on the Global Earthquake Activity Rate model, which is available in Temblor, the likely earthquake in your lifetime for this part of California is M=6.25+. This model uses global strain rates and seismicity since 1977 to forecast future events. What this suggests is that a M=7.5 earthquake would be a unique event, but nonetheless possible.

This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for Northern California. What this shows is that around the Maacama and Bartlett Springs faults, a M=6.25+ earthquake is likely in your lifetime.

The Maacama Fault also deserves a bit of extra attention because at its southernmost extent in Santa Rosa, there is a stepover with the Rodgers Creek Fault. Because of their close proximity, it is possible that an earthquake originating on the Rodgers Creek Fault, could rupture onto the Maacama Fault, or vice versa. This has serious implications for the city of Santa Rosa, which suffered heavy damage in the 1906 earthquake (see below). What all of this indicates is that while the San Andreas may get all the publicity, Northern California has many other large faults capable of generating large earthquakes.

This picture shows the city of Santa Rosa following the 1906 earthquake. The caption in this figure reads: “Dear Blossom, This is as we found it. Much love, Mother.”


Ohlin, H.N., McLaughlin, R.J., Moring, B.C., and Sawyer, T.L., 2010, Geologic map of the Bartlett Springs Fault Zone in the vicinity of Lake Pillsbury and adjacent areas of Mendocino, Lake, and Glenn Counties, California: U.S. Geological Survey Open-File Report 2010–1301, scale 1:30,000. (Available at

Robert J. McLaughlin, Andrei M. Sarna-Wojcicki, David L. Wagner, Robert J. Fleck, V.E. Langenheim, Robert C. Jachens, Kevin Clahan, and James R. Allen, Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California, 2012, Geosphere, Vol. 8, Issue 2, DOI:10.1130/GES00682.1

See the full article here .

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Stem Education Coalition

You can help many citizen scientists in detecting earthquakes and getting the data to emergency services people in affected area.
QCN bloc

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).


BOINC WallPaper

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
QCN Quake Catcher Network map