Evaluating Source and Site Effects in Peak Ground Displacement Models for Earthquake Magnitude Calculation

Jack Sheehan, & Valerie J. Sahakian

Published August 16, 2021, SCEC Contribution #11549, 2021 SCEC Annual Meeting Poster #246 (PDF)

Peak ground displacement (PGD) ground-motion models (GMMs) derived from high-rate Global Navigation Satellite System (HR-GNSS) data are becoming more widely used in earthquake and tsunami early warning applications, both for magnitude and ground-motion estimation. Magnitude scaling laws derived from strong-motion measurements can suffer drastically from saturation effects, but estimates from PGDs do not saturate. This is particularly important in early-warning applications, as accurate magnitude estimates in the initial minutes following an earthquake can save lives. PGD GMMs are, however, relatively new, and little is known about the physical causes of their associated earthquake and site variability.

This study aims to evaluate the cause of the individual earthquake and station biases in PGD models. We hypothesize these effects could be caused by earthquake mechanisms, hypocenter estimations, or crustal effects. We use the largest PGD earthquake dataset currently available, published as an open database alongside Ruhl et al., (2019) which includes 29 earthquakes and 3,433 three-component station recordings. First, using the predicted PGD model proposed by Crowell, as well as the observed PGD equation from Melgar et al., (2015), we compute dataset residuals for all records in the dataset. We calculate 94.3% of PGD residuals within +/- .02 meters, as well as a net residual of -0.001 meters. There is no consistent overall magnitude bias. Next, we compute source and site effects in R, using a mixed effects regression on the residuals. We test earthquake mechanism as a potential source effect by plotting each earthquake’s resulting site residual versus hypocenter distance for reverse, strike-slip, and normal earthquakes. We plan to test hypocenter estimation by comparing residuals calculated using initial location estimates and those determined by the National Earthquake Information Center http://earthquake.usgs.gov/). We will also test peak slip and rupture velocity as a potential source effect for each earthquake. Current results indicate earthquake mechanism does not play a significant role in the success of the model. For each of our additional hypotheses, updated results will be presented at the meeting.

Key Words
PGD, GNSS, source effects, model

Citation
Sheehan, J., & Sahakian, V. J. (2021, 08). Evaluating Source and Site Effects in Peak Ground Displacement Models for Earthquake Magnitude Calculation. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology