DYNAMIC EARTHQUAKE TRIGGERING OF LONG PERIOD EVENTS IN THE SAN MIGUEL VOLCANO

Do earthquakes and volcanoes interact? Energy propagating from earthquakes can change the stress in an area and trigger earthquakes remotely (more than 2 faults lengths away from an epicenter). The internal state and activity of an active volcano may be disturbed by changes caused by the passage of seismic energy. The San Miguel Volcano, located in El Salvador, is a highly active stratovolcano that last erupted in December 2013. San Miguel has not been extensively studied and presents a significant hazard to the region actively releasing volcanic gases, historic flank eruptions, and fissure activity. To investigate the internal processes of the volcano, we used data collected from a network of six UTEP seismic sensors recording ground movement from 2007-2008 located around the volcano. Manually analyzing the seismic data, we found 9 regional earthquakes that appear to have triggered a long period response from the volcano mostly during the passage of the surface waves. We compared 5 earthquakes of similar magnitude and distance that did not trigger a long period signal. These earthquakes lacked a strong surface wave signal based on the (LG/P) ratio. We calculated the peak dynamic stresses (PDS) of the triggering earthquakes and found that they had a PDS of at least 0.01 mPa. We conclude that the long period response of the volcano was triggered by the interaction of the volcano and the abrupt surface waves from the regional earthquakes, and we are currently investigating mechanisms for this long period response.