1969 Santa Rosa earthquakes

Pair of earthquakes that struck Santa Rosa, California May 2025 February 2025 1969 Santa Rosa earthquakes doublet 1969-10-02 04:56 1969-10-02 06:19 1969 10 01 803001 803006 ushis3058 ushis3059 USA California 5.6 and 5.7 w y 9.6 km 38.467 -122.692 region:US-CA_type:event inline,titlehttps://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/4502 Significant Earthquake Information National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information. 10.7289/V5TD9V7K 22 March 2024 United States (Santa Rosa) VII VIII Yes 1 dead thumb|Geological structures near Santa Rosa, showing the epicenters of the 1969 earthquakes At 04:56 and 06:19 UTC on October 2, 1969 (21:56 and 23:19 PDT October 1), a pair of earthquakes of magnitude 5.6 and 5.7, respectively, struck the city of Santa Rosa, California, killing one person and damaging buildings. The maximum felt intensity for the two events was VII (Very strong) and VIII (Severe) respectively on the Mercalli intensity scale.https://ehp4-earthquake.cr.usgs.gov/regional/nca/siteresponse/siteresponse0207.pdf Site Response in the Northern San Francisco Bay Area, California Bergen K.J. Fletcher J.B. Boatwright J. Langeheim V. amp 2007 United States Geological Survey 5 September 2011 https://web.archive.org/web/20120305190850/http://ehp4-earthquake.cr.usgs.gov/regional/nca/siteresponse/siteresponse0207.pdf 2012-03-05 dead The $8.35 million cost of the earthquakeshttps://earthquake.usgs.gov/earthquakes/states/events/1969_10_02.php Santa Rosa, Sonoma County, California 1969 October 02 04:46 and 06:19 UTC (local October 1) Magnitude 5.6 and 5.7 United States Geological Survey 6 September 2011 https://web.archive.org/web/20161201081624/https://earthquake.usgs.gov/earthquakes/states/events/1969_10_02.php 2016-12-01 dead went mostly to replace buildings damaged beyond repair. There were at least 200 aftershocks after the initial pair of earthquakes. At the time they were the largest earthquakes to affect the northern San Francisco Bay Area since the 1906 San Francisco earthquake. Tectonic setting The current tectonics of northern California are mainly controlled by the San Andreas Fault system, the zone of dextral strike-slip faulting that accommodates displacement between the North American plate and the Pacific plate along this transform boundary. In addition to the San Andreas Fault itself there are numerous other sub-parallel dextral strike-slip faults that take up some of the plate boundary motion distributed through a zone more than 100 km wide. The 1969 earthquakes and most of their aftershocks occurred along the Healdsburg Fault, which lies between the Maacama Fault and the Rodgers Creek Fault, linked to them by right step-overs.Wong I.G. Bott J.D.J. 1995 A new look back at the 1969 Santa Rosa, California, earthquakes Bulletin of the Seismological Society of America 85 1 334–341 http://bssaonline.org/cgi/content/abstract/85/1/334 5 September 2011 3 April 2010 https://web.archive.org/web/20100403170606/http://www.bssaonline.org/cgi/content/abstract/85/1/334 dead These faults form a continuation of the Hayward Fault Zone north of San Francisco Bay.Castillo D.A. Ellsworth W.L. 1993 Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in Northern California: Implications for the Development and Evolution of a Young Transform Journal of Geophysical Research 98 B4 6543–6560 http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1396&context=usgsstaffpub&sei-redir=1#search=%22healdsburg%20fault%20map%22 5 September 2011 1993JGR....98.6543C 10.1029/92JB02866 subscription Earthquake The two earthquakes occurred about a kilometer apart, a few kilometers north of Santa Rosa, close to the trace of the Healdsburg Fault.https://pubs.usgs.gov/of/2008/1009/of2008-1009_sheet2.pdf Open-File Report 2008-1009 Sheet 2 of 3 McLaughlin R.J. Langenheim V.E. Sarna-Wojcicki A.M. Fleck R.J. McPhee D.K. Roberts C.W. McCabe C.A. Wan E. amp 2008 Geologic and Geophysical Framework of the Santa Rosa 7.5' Quadrangle, Sonoma County, California United States Geological Survey 8 September 2011 The focal depths of the two mainshocks were 9.6 km and 10.4 km respectively. The first shock was described as "violent or explosive" by residents and the main shaking lasted for 15 seconds.Cloud W.K. Hill D.M. Huffman M.E. Jennings C.W. McEvilly T.V. Nason R.D. Steinbrugge K.V. Tocher D. Unger J.D. Youd T.L. T. Leslie Youd amp 1970 The Santa Rosa earthquakes of October, 1969 California Geology 23 3 http://www.conservation.ca.gov/cgs/geologic_hazards/earthquakes/pdfs/Documents/CG_MAR1970.pdf 6 September 2011 https://web.archive.org/web/20120319214854/http://www.conservation.ca.gov/cgs/geologic_hazards/earthquakes/pdfs/Documents/CG_MAR1970.pdf 19 March 2012 dead Earthquake epicenter Coordinates First earthquake 38 28.4 N 122 43.0 W type:event_region:US-CA dec Second earthquake 38 27.9 N 122 43.1 W type:event_region:US-CA dec Damage The earthquake caused severe damage in some areas of Santa Rosa, affecting many buildings, bringing down chimneys, causing sidewalks to buckle and rupturing underground pipes. The lack of casualties and the low number of injuries is ascribed to the earthquakes being in the evening, when there were few pedestrians in the streets. The degree of damage associated with the earthquakes was greater than expected for their magnitude, with many older building left beyond repair. Gravity data have been used to show the presence of two sedimentary basins, separated by the Trenton ridge, which is associated with the northeast-dipping Trenton thrust fault. Modeling of the ground motion for the 1906 and 1969 earthquakes shows increased shaking at the northeastern edge of the southern basin, where Santa Rosa is situated.McPhee D.K. Langenheim V.E. Hartzell S. McLaughlin R.J. Aagaard B.T. Jachens R.C. McCabe C amp 2007 Basin Structure beneath the Santa Rosa Plain, Northern California: Implications for Damage Caused by the 1969 Santa Rosa and 1906 San Francisco Earthquakes Bulletin of the Seismological Society of America 97 5 1449–1457 10.1785/0120060269 https://zenodo.org/record/1235787/files/article.pdf 5 September 2011 2007BuSSA..97.1449M Aftermath Following the relatively high level of damage caused by the 1969 earthquakes, the city set about retrofitting buildings to improve their earthquake resistance by adding for instance cross-bracing to unreinforced masonry structures. The first buildings to be retrofitted were the St. Rose Church and Parish hall due to their high level of occupancy and lack of reinforcing. The safety standards adopted in Santa Rosa in 1970 provided a model for other cities in California when the state brought in requirements for retrofitting.Hecker S. Kelsey H. Prentice C.S. 1906 San Francisco earthquake centennial field guides: field trips associated with the 100th anniversary conference, 18–23 April 2006, San Francisco, California https://books.google.com/books?id=CwchZE54dWYC&pg=PA339 5 September 2011 7 2006 Geological Society of America 978-0-8137-0007-6 352 History and pre-history of earthquakes in wine and redwood country, Sonoma and Mendocino counties California An analysis of the effects on structures in Santa Rosa showed that it was necessary to design buildings using dynamic principles rather than just static, even in the case of a moderate intensity earthquake.Robertson L.E. Tall building criteria and loading https://books.google.com/books?id=l76DdHXCLn0C&pg=PA115 5 September 2011 Monograph on Tall Buildings 150 1980 Council on Tall Buildings and Urban Habitat 978-0-87262-237-1 115 See also List of earthquakes in 1969 List of earthquakes in California List of earthquakes in the United States References External links 803001 Santa Rosa, 1969 1969 Category:History of Sonoma County, California Category:History of Santa Rosa, California Earthquakes Category:Earthquake clusters, swarms, and sequences