California, California earthquake swarm, earthquake hazard, earthquake watch, earthquakes, geothermal, Imperial Fault, induced earthquakes, Salton Sea, Salton Trough Fault, San Andreas earthquake, San Andreas Fault, San Jacinto Fault, seismicity, Southern California, stupidity
“Geothermal power is a growing energy source; however, efforts to increase production are tempered by concern over induced earthquakes. Although increased seismicity commonly accompanies geothermal production, induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters. We show that at the Salton Sea Geothermal Field, the total volume of fluid extracted or injected tracks the long-term evolution of seismicity.” (Brodsky et. al. 2013)
Why would they take such risks as putting geothermal production facilities on major earthquake faults?
“The Salton Sea and surrounding basin sits over the San Andreas Fault, San Jacinto Fault, Imperial Fault Zone, and a “stepover fault” shear zone system. Geologists have determined that previous flooding episodes from the Colorado River have been linked to earthquakes along the San Andreas Fault. Sonar and other instruments were used to map the Salton Sea’s underwater faults during the study. During the period when the basin was filled by Lake Cahuilla, a much larger inland sea, earthquakes higher than magnitude 7 occurred roughly every 180 years, the last one occurring within decades of 1700. Computer models suggest the normal faults in the area are most vulnerable to deviatoric stress loading by filling in of water. Currently, a risk still exists for an earthquake of magnitude 7 to 8. Simulations also showed, in the Los Angeles area, shaking and thus damage would be more severe for a San Andreas earthquake that propagated along the fault from the south, rather than from the north. Such an earthquake also raises the risk for soil liquefaction in the Imperial Valley region.” https://en.wikipedia.org/wiki/Salton_Sea
“October 04, 2016 | By Annie Reisewitz
New Fault Discovered in Earthquake-Prone Southern California Region
A swarm of nearly 200 small earthquakes that shook Southern California residents in the Salton Sea area last week raised concerns they might trigger a larger earthquake on the southern San Andreas Fault. At the same time, scientists from Scripps Institution of Oceanography at the University of California San Diego and the Nevada Seismological Laboratory at the University of Nevada, Reno published their recent discovery of a potentially significant fault that lies along the eastern edge of the Salton Sea.
The presence of the newly mapped Salton Trough Fault, which runs parallel to the San Andreas Fault, could impact current seismic hazard models in the earthquake-prone region that includes the greater Los Angeles area. Mapping of earthquake faults provides important information for earthquake rupture and ground-shaking models, which helps protect lives and reduce property loss from these natural hazards.
The National Science Foundation (NSF)-funded study appears in the Oct. 2016 issue of the journal Bulletin of the Seismological Society of America.
Recent studies have revealed that the region has experienced magnitude-7 earthquakes roughly every 175 to 200 years for the last thousand years. A major rupture on the southern portion of the San Andreas Fault has not occurred in the last 300 years.
The findings provide much-needed information on the intricate structure of earthquake faults beneath the sea and what role it may play in the earthquake cycle along the southern end of the San Andreas Fault.” See entire press release here: http://ucsdnews.ucsd.edu/pressrelease/new_fault_discovered_in_earthquake_prone_southern_california_region
“Anthropogenic seismicity rates and operational parameters at the Salton Sea Geothermal Field. Science. 2013 Aug 2;341(6145):543-6. Epub 2013 Jul 11.
Brodsky EE1, Lajoie LJ. Science. 2013 Dec 20;342(6165):1446.
Geothermal power is a growing energy source; however, efforts to increase production are tempered by concern over induced earthquakes. Although increased seismicity commonly accompanies geothermal production, induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters. We show that at the Salton Sea Geothermal Field, the total volume of fluid extracted or injected tracks the long-term evolution of seismicity. After correcting for the aftershock rate, the net fluid volume (extracted-injected) provides the best correlation with seismicity in recent years. We model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time.“https://www.ncbi.nlm.nih.gov/pubmed/23845943
“Characterizing Potentially Induced Earthquake Rate Changes in the Brawley Seismic Zone, Southern California Andrea L. Llenos and Andrew J. Michael https://pubs.er.usgs.gov/publication/70176199
“Natural or Induced: Identifying Natural and Induced Swarms from Pre-production and Co-production Microseismic Catalogs at the Coso Geothermal Field” Martin Schoenball 1, 2 , J. Ole Kaven 2 , Jonathan M.G. Glen 2 and Nicholas C. Davatzes 1 1 Earth and Environmental Science, Temple University, Philadelphia, Penn. 2 GMEG Science Center, U.S. Geological Survey, Menlo Park, Calif.
“Increased levels of seismicity coinciding with injection of reservoir fluids have prompted interest in methods to distinguish induced from natural seismicity. Discrimination between induced and natural seismicity is especially difficult in areas that have high levels of natural seismicity, such as the geothermal fields at the Salton Sea and Coso, both in California…”
“Induced seismicity in Basel led to suspension of its hot dry rock enhanced geothermal systems project. A seismic-hazard evaluation was then conducted, resulting in the cancellation of the project in December 2009. Basel, Switzerland sits atop a historically active fault and most of the city was destroyed in a magnitude 6.5 earthquake in 1356. But the Basel project, although it had established an operational approach for addressing induced earthquakes, had not performed a thorough seismic risk assessment before starting geothermal stimulation./ Seismic events in Basel reached the trip point of Richter Magnitude ML 2.9 six days after the main stimulation was started on December 2, despite precautionary reduction of the injection rate earlier that same day upon reaching earlier “soft” thresholds. However, further tremors exceeding magnitude 3 were recorded on 6 January (measuring 3.1), 16 January 2007 (3.2), and 2 February 2007 (3.2).” https://en.wikipedia.org/wiki/Induced_seismicity_in_Basel