Local Magnitude (ML) Determination for Earthquakes in the Yellowstone National Park Region, USA

Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

We have derived new local magnitude (M_L) distance and station corrections for earthquakes in the Yellowstone National Park region (YP) using data from a Wood-Anderson and 19 broadband stations located in the area. The University of Utah Seismograph Stations (UUSS) has used the Richter (1958) distance corrections (R58) to calculate M_L for earthquakes in the Intermountain Seismic Belt (ISB) since 1962. Pechmann et al. (2007) validated the use of R58 for the ISB and developed a set of M_L station corrections which was later expanded. However, their evaluation of R58 for the YP part of the ISB was inconclusive since they only had sufficient data from 5 of 20 stations used in our study. Our primary goal was to increase the fraction of YP earthquakes with M_L determinations, which was 40% in 2015-2019. We address this goal by developing a more complete and accurate set of M_L corrections for YP stations with our larger dataset. Another key goal was to derive distance corrections specifically for YP, using hypocentral instead of epicentral distance.

Using a spatially balanced subset of the UUSS YP catalog, we applied a non-parametric inversion method to derive the new distance and station corrections (YP20) simultaneously. Overall, we find YP20 indicates faster attenuation than R58, but with increased amplitudes from 75–150 km (stable over 1000 bootstraps), possibly related to post-critical Moho reflections. We recalculated M_L using YP20 for ~3950 earthquakes and compared the new (M_L,YP) to existing (M_L,UUSS) magnitudes. Although distance and station corrections for M_L,YP and M_L,UUSS are different, they give similar M_Ls with no significant systematic difference in the range 1 < M_L,UUSS < 3.6. In addition, M_L,YP has better agreement with moment magnitudes (M_w) (3.2 < M_w < 4.5 calculated by UUSS and Saint Louis University. The absolute values of the new M_L,YP station corrections are generally smaller than those of the current UUSS station corrections. We suggest that previous M_L station corrections compensated, in part, for inaccuracies introduced by using R58.

Presenting Author: James Holt

Authors