Dynamic triggering of microearthquakes in three geothermal/volcanic regions of California

Abstract

Geothermal/volcanic regions are most susceptible to local earthquake triggering by regional and remote earthquakes. Transient stresses caused by surface waves of these earthquakes can activate critically stressed faults. Though earthquakes can be triggered in geothermal/volcanic regions, it is less understood how these regions differ in their triggering responses to distant earthquakes. We conduct a systematic survey of local earthquakes triggered by distant earthquakes in three geothermal/volcanic regions of California: Long Valley Caldera, Coso Geothermal Field, and Geysers Geothermal Field. We examine waveforms of distant earthquakes with magnitudes ≥ 5.5 occurring between 2000 and 2012 and compute β statistics to confirm the significance of our findings. We find that Long Valley, Coso, and Geysers vary in triggering frequency-2.0%, 3.8%, and 6.8% in the 12 year period, respectively-and when compared to the triggering of deep tectonic tremors along the Parkfield-Cholame section of San Andreas Fault (9.2% in the 12 year period). Stress triggering thresholds vary among the regions with Long Valley having the highest of~5 kPa and 1 kPa for the other regions. Because dynamic stresses from distant earthquakes are similar in these three regions, the varying triggering behavior likely reflects faults having a tendency to be at or near failure. This is compatible with Geysers having a higher a value in the Gutenberg-Richter relationship and higher geothermal productivity than the other two regions. The observation of more frequent triggering of tremor than microearthquakes is consistent with recent laboratory studies on increasing triggerability with lower effective stress.

Remote triggering of seismicity at Japanese volcanoes following the 2016 M7.3 Kumamoto earthquake

“…3c, station ANNH), the dynamic stress changes are on the order of 5-11 kPa. These last values are similar to the minimum dynamic stress values, of a few kPa, reported in other studies as capable of triggering earthquakes (e.g., Aiken and Peng 2014). van der Elst and Brodsky (2010) report minimum dynamic stresses that could trigger earthquakes on the order of 0.1 kPa or even lower, using an improved approach.…”

“…Nevertheless, two main classes of models (Hill and Prejean 2015) are used to explain the triggering by dynamic stresses: (1) direct triggering by frictional failure and (2) triggering through excitation of crustal fluids. As documented in previous studies (e.g., Aiken and Peng 2014), fluids are active agents in geothermal and volcanic areas, where dynamic triggering is often observed.…”

“…The threshold dynamic stresses that can trigger seismicity are of a few kPa (e.g., Aiken and Peng 2014); however, larger thresholds have been reported for Japan (e.g., van der Elst and Brodsky 2010). We hypothesize that a change in triggering conditions may have taken place after the 2011 Tohoku-oki earthquake, in particular at volcanic areas in NE Japan.…”

Triggering and decay characteristics of dynamically activated seismicity in Southwest Japan

“…As documented in previous studies (e.g. Aiken & Peng 2014), fluids are active agents in volcanic and geothermal areas, which may explain the more vigorous and widespread triggering in such regions. Miyazawa (2011) reported an earthquake triggering front, propagating at about the same speed as the Rayleigh waves (of 10-20 s period), from the 2011 Tohoku-oki earthquake; the furthest seismic Triggering and decay characteristics 1011 activation has been observed in southern Kyushu, at the Ibusuki volcanic area, at about 1350 km epicentral distance.…”

Measuring seismicity diversity and anomalies using point process models: case studies before and after the 2016 Kumamoto earthquakes in Kyushu, Japan

“…In this respect, we have quantitatively analyzed this type of off-fault activity. There are various physical mechanisms that operate to trigger earthquakes (Hill and Prejean 2015) either via increased static shear stress or fault weakening by dynamic stresses where crustal fluids are active agents (e.g., Terakawa 2014;Aiken and Peng 2014). In this respect, we have quantitatively estimated how the background rate of the non-stationary ETAS model fluctuated on the northern side of the focal fault segments of the Kumamoto earthquakes, as shown in Fig.…”