Aftershock Monitoring with a Heterogeneous Seismic Network

Date: 4/24/2019

Time: 11:15 AM

Room: Grand Crescent

The Mw 4.2 Dover, DE, earthquake in 2017 represented an opportunity to evaluate seismicity in a passive margin setting, motivating a rapid deployment of instruments in order to record aftershocks. Within 24 hours of the main shock, personnel from the Lamont-Doherty Earth Observatory, the Department of Terrestrial Magnetism of the Carnegie Institution for Science, the University of Maryland, Lehigh University, and the USGS mobilized to install a mix of instruments in the epicentral area. The deployment included 10 Fairfield Nodal ZLand three-component 5-Hz geophones, which operated on self-contained batteries for 37-40 days, as well as four Nanometrics Trillium 120 Compact posthole broadband seismometers, which used solar power and ran for 42 days until removal.

Using template-matching, we detect several dozen aftershocks, all with magnitudes ≤ 1.3, and locate a subset using a 1D model developed by modeling waveforms of the M4.2 main shock at regional broadband stations down to a 5-second period. We discuss the aftershock productivity and locations in the context of East Coast seismicity. We observe that a single broadband station detects more aftershocks than all 10 nodal stations combined, due to relatively high noise levels on the nodals, even though the frequency range of interest (4-40 Hz) is optimal for the 5-Hz geophone. We compare the signal power during the detection window for nodal and broadband data and relate that to estimated local magnitude of detected aftershocks. Finally, we analyze the relative performance of the three-component nodal geophones and the compact broadband seismometers, and discuss the associated tradeoffs when designing aftershock-monitoring deployments.

Presenting Author: Karen M. Pearson

Authors