Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 14
Presentation Time: 8:00 AM-5:30 PM


MORTON, Emily A. and BILEK, Susan L., Earth and Environmental Science, Geophysics, New Mexico Tech, Socorro, NM 87801,

The release of energy during an earthquake changes the stress state and seismicity both locally and remotely. Far-field stress changes can lead to triggered earthquakes coinciding with the arrival of the surface waves. This dynamic triggering is found to occur in a variety of tectonic settings, but in particular magmatic regions. Therefore we would expect to see this process occurring above the Socorro Magma Body (SMB) within the Rio Grande Rift. To test this, I examined data from 319 large earthquakes (teleseisms) MW ≥ 6.0 between January 15, 2008 and November 30, 2009 recorded on 21 EarthScope USArray stations and 10 Socorro Seismic Network short-period stations. Using a high-pass filter to remove the low-frequency waves from the teleseism on the EarthScope stations, waveforms were windowed around the time of the teleseism and analyzed to detect high-frequency triggered local earthquakes. 91 local events were found following 66 teleseisms. The majority of the local events occur well after the arrival of the surface waves indicating that they are independent of the teleseism, or evidence of delayed dynamic triggering, which is marked by an increase in seismicity relative to background rates. Preliminary inspection of the period before the wave passage shows an increase in seismicity after the teleseism wave arrival for more than half possibly triggered events, indicating delayed triggering. The majority of local events are located above the SMB, with some events spread throughout New Mexico, suggesting while triggering appears more conducive above the SMB, it is not limited to this area and can be spread throughout the rift. While dynamic stress values acting on faults are dependent on wave propagation direction relative to fault orientation, the locations of the teleseisms show no preferential source region for triggering in New Mexico. Further work includes determining if triggering and triggering delay is dependent on the amplitude of the telseism waves.