Since we have exceeded the average, many people use the term “overdue,” but it’s more complicated than that. Maybe you’ve heard that the “Big One is overdue” on the San Andreas Fault. Bay Area Retrofit assumes no responsibility or liability for use by homeowners, contractors, engineers, or anyone else of the information provided on this site. Many of the sites paleoseismologists have been studying are along key sections of the SAFZ where there is a large population or major infrastructure that would be affected by a large earthquake in the future. The 1906 San Francisco earthquake is estimated to have been in the 7.8 range (and possibly even larger.) On October 21, 1868, a magnitude 6.8 earthquake struck the San Francisco Bay area. Here is a shorter eye-opening 7-minute TV clip on the Cascadia Fault. Along the southernmost San Andreas, from Palm Springs to the Salton Sea, earthquakes happen infrequently, about every 200-300 years. The transform boundary initiated about 30 million years ago when a spreading ridge separating the Pacific and Farallon Plates intersected with the North American continental crust near what is now Los Angeles, California (Fig. The entire San Andreas fault system is more than 800 miles long and extends to depths of at least 10 miles within the Earth. Prior to 1300, the intervals are shorter, about 200 years. The faults shown here are represented by simple lines which do not convey how complicated they can be. We have identified 4 common types of house and have written web pages and made videos to show you how to retrofit them. The SAFZ is the main part of the boundary between the Pacific tectonic plate on the west side and the North American plate on the east side. The In 1836 there was a large earthquake but the larges was felt on October 21, 1868. Let's start in southern California and work our way north. The San Andreas fault caused the biggest earthquakes in California with an approximate magnitude 7.9 in 1857 (Southern California) and 1906 (San Francisco). DAMAGE LIKE THIS IS A VERY REAL POSSIBILITY WHEN THE CASCADIA SUBDUCTION ZONE RUPTURES, Retrofitting Bay Area Homes for 25 Years and Still Counting, The Coming Bay Area Earthquake: 2010 Update of Scenario for a Magnitude 7.0 Earthquake on the Hayward Fault. This fault, called a “tectonic time bomb,” is about 74 miles long. Fault-plane reflections reveal that two of these faults, the San Andreas and Hayward, dip toward each other below seismogenic depths at 60?? Sorry for posting all the documentaries and I can’t really tell you which one is best. Map of faults in southern California. Four urban areas of the San Andreas Fault System in Northern California have accumulated a sufficient amount of energy to produce major earthquakes, a new study finds. The fault has been creeping about 4.6 mm/yr (0.2 inches/yr) for the last several decades, but that is only half of the long-term slip rate, so stress is building upon this fault. Along the San Francisco peninsula no detectable slip occurs (less than 1.5 mm/yr) at the surface, but appreciable strain is accumulating. The San Andreas Fault and 6 other significant fault zones are present in the Bay Area: the Calaveras, Concord-Green Valley, Greenville, Hayward, Rodgers Creek, and San Gregorio Faults. The San Francisco Bay area is crossed by several right-lateral strike-slip faults of the San Andreas fault zone. At that location, the record is about 1000 years long, and in that time period, there are about 9 large earthquakes recorded in the sediments, including the 1857 rupture. Public domain.). (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. San Francisco Bay Area Earthquakes: The Hayward and San Andreas Faults are probably the most studied earthquake faults in the world, so a lot is known about them. 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. 408-664-6355 The threat to San Francisco from the Hayward fault was recognized by A. C. Lawson in 1908 in Report of the State Earthquake Commission, The California earthquake of April 18, 1906, p. 447: "The foot of Market Street, San Francisco, is about midway between the San Andreas rift and the fault scarp upon which movement occurred in 1868. In detail, the fault is a complex zone of crushed and broken rock from a few hundred feet to a mile wide. Since then, research has indicated that the likelihood of a Hayward quake is greater and more threatening to the 7 million Bay Area residents than a San Andreas … 510-548-1111. The “zone” part of the name means it’s a system with the main fault and many sub-parallel faults that all together take up the motion between the two plates. In 2014, a paleoseismology site at Hael Creek on the Maacama fault reiterated the results found on the Hayward fault to the south – creeping with infrequent large earthquakes, and a large one expected in the not-too-distant future. The Hazel Dell site near Corralitos, CA was trenched in 2013 to characterize the Santa Cruz Mountains section of the San Andreas Fault. (Credit: Kate Scharer, USGS. Geographic Names Information System (GNIS), Mapping, Remote Sensing, and Geospatial Data, Earthquake Outlook for the San Francisco Bay Region 2014—2043, Map of active faults and historic ruptures in California, New Information About the San Andreas Fault, Catching Glimpses of Centuries-Old Earthquakes, Science of the New Madrid Seismic Zone - Paleoseismology, UCERF3: A New Earthquake Forecast for California’s Complex Fault System. This means that earthquakes as large as M=7.4 are possible on both sides of San Francisco Bay, rather than just on the San Andreas, as we had thought before. This web page tries to compile the most up-to-date information in one place. The Hayward Fault is 40 miles long and about 8 miles deep and trends along the east side of San Francisco Bay. ?, respectively, and persist to the base of the crust. Scientists are working to improve forecasts that estimate how often future earthquakes will occur and how much the ground will shake so engineers and planners will know where to focus efforts to mitigate the effects of damaging earthquakes. Near fault shear strain rates are 0.6 ± 0.1 μstrain/yr (engineering) with direction N47°W ± 9. Basically, because it’s a big fault that is close to some big cities. The paleoseismic data on different parts of the San Andreas Fault Zone are all telling us that some sections appear to be past the average, or "overdue" for a significant earthquake. 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