By David Jacobson, Temblor
Check your seismic hazard rank
In a move prompted by the “very real” threat of earthquakes, Los Angeles County sued state regulators yesterday to keep the Aliso Canyon natural gas storage facility closed. The facility was closed after a massive leak was discovered on October 23, 2015, and lasted four months, in the process releasing nearly 100,000 tons of methane. This made it the worst natural gas leak in U.S. history. Additionally, people became sick, and thousands were forced to leave their homes.
The lawsuit accuses California state oil and gas regulators of prematurely ending a safety review before fully knowing the seismic risk of Aliso Canyon and the cause of the 2015-2016 gas leak. The oil and gas division could not comment on these accusations.
Aliso Canyon is in northwest Los Angeles County, approximately 40 km from downtown Los Angeles. Since 2006, there have been 16 M=2.0-4.7 earthquakes in the canyon. Additionally, the Santa Susana fault within the Sierra Madre fault zone runs right underneath and next to the natural gas storage facility. Furthermore, one of the state’s Alquist-Priolo fault zones is right next to the facility. These zones are created as a way to increase public safety by prohibiting residential structures from being erected. While the gas storage plant is not residential, the presence of an Alquist-Priolo fault zone illustrates the seismic concern.
In addition to the faults in the immediate vicinity of Aliso Canyon, studies by Professor Matthew d’Alessio found that in the M=6.7 1994 Northridge earthquake, shaking was severe enough at the plant that one of the wells collapsed. So, it is not only local sources that must be considered. Similar well collapses have also been noted worldwide in earthquakes smaller than M=6.3.
Further evidence supporting the seismic hazard of the area is both the Temblor Hazard Rank of 81, and the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor. The hazard rank is based on the likelihood of experiencing damage shaking, and the GEAR model forecasts the likely earthquake magnitude in your lifetime anywhere on earth. This model forecasts a M=6.5-6.75 earthquake is likely in your lifetime for the location of Aliso Canyon. Such an earthquake could cause significant damage to the gas storage facility, and result in the release of natural gas.
Overall, the primary objective of this lawsuit is public safety. Because the exact cause of the 2015-2016 gas leak is not definitively known, Los Angeles County is taking measures to prevent the facility from opening prematurely. Additionally, as the region has the potential to see experience significant shaking from large magnitude earthquakes, the county, and professors like Matthew d’Alessio believe that more studies are needed to fully understand the seismic risk of Aliso Canyon. Should more information come in regarding this lawsuit, we will update this post.
Reference
Los Angeles Daily News