An Unwanted Long-Period Step-Response Signal Recorded During Local Alaska Earthquakes

Session: Recent Advances in Very Broadband Seismology
Type: Oral
Date: 4/30/2020
Time: 11:15 AM
Room: 215 + 220
Description: 

Previous seismological studies have documented step-response signals recorded during earthquakes, whereby the true long-period ground motion is obscured by an instrumental step response initiating with the arrival of high-frequency, high-amplitude earthquake waves. Here we examine 17 earthquakes in central Alaska with magnitudes between Mw 3.2 and 5.0. We document 94 occurrences of the step-response signal at 26 different stations, including 13 within the FLATS deployment centered on Nenana basin (FLATS: Fault Locations and Alaska Tectonics from Seismicity). For most recorded step-response signals, the epicentral distances range from 5 km to 150 km and the signals are dominantly on the horizontal components, suggesting the influence of tilting. In August of 2018, a team of UAF and Nanometrics scientists installed a Cascadia instrument adjacent to an existing FLATS sensor. The Cascadia includes a Trillium Compact 120s seismometer and a Titan Class A accelerometer. During the full-year deployment, the colocated sensors recorded two local earthquakes that produced step-response signals due to local tilting, whereby "local" refers to distances within 1 m of the sensor. Our observations lead to a key question: How can we record the long-period seismic wavefield at near-field stations within sedimentary basins? We will discuss options for possible improvements to installations, instruments and data processing, toward mitigating the occurrences of step-response signals masking long-period regional ground motion.

Presenting Author: Carl Tape

Authors