V_S30 Characterization of Texas, Oklahoma, and Kansas Using the P-Wave Seismogram Method

Abstract

The P-wave seismogram method is used to develop estimates of the time averaged shear wave velocity of the upper 30 m ( V S30) at 251 seismic stations in Texas, Oklahoma, and Kansas. Geologic conditions at the sites are documented using large-scale geologic maps. The V S30 values from the P-wave seismogram method agree well with the limited in situ measurements across the study area and correlate well with the mapped geologic units. Compared with the V S30 proxy values assigned to the stations by the Next Generation Attenuation–East (NGA-East) project, the P-wave seismogram method generally produces larger V S30 estimates. These differences are likely due to the fact that very few V S measurements in Texas, Oklahoma, and Kansas were available for use in the development of the NGA-East proxies. Analysis of the P-wave seismogram V S30 values indicates that, in this geographic area, incorporating rock type along with geologic age better distinguishes the average V S30 of these materials than geologic age alone.

Ground Motion Model for Small-to-Moderate Earthquakes in Texas, Oklahoma, and Kansas

“…To assess the accuracy of both the P-wave seismogram V S30 estimates and geologybased V S30 proxies, we compare them with V S30 values derived from a series of in-situ V S measurements ( Figure 3) recently performed at seismic station locations in the Dallas-Fort Worth area using a combination of linear array active-source and two-dimensional array ambient-wavefield surface wave testing by Cox et al (2017). These seismic station locations coincide with locations where P-wave seismogram estimates were available by Zalachoris et al (2017). Also shown is the measured V S30 at the Wichita Mountains seismic station (US.WMOK) in Oklahoma (V S30 ¼ 1,859 m∕s, Yong et al 2015), located on Paleozoic granite.…”

“…For soft sites (V S30 < 200 m∕s), the recordings indicate motions 40% smaller than predicted by the HA15 model at T ¼ 0.1 s, while the observations are almost 70% smaller at T ¼ 1.0 s. The discrepancies between the HA15 model and recordings at softer sites in Texas, Oklahoma, and Kansas are likely due to the fact that HA15 utilizes the BSSA14 WNA site amplification model. As discussed in Zalachoris et al (2017), the depth to rock (i.e., V S30 > 760 m∕s) in Texas, Oklahoma, and Kansas tends to be small even at sites with small V S30 . In WNA, sites with small V S30 typically are characterized by deeper sediments that generate larger amplification, particularly at longer periods.…”

“…Finally, if neither field measurements or P-wave seismogram estimates were not available, proxybased V S30 values from Table 1 were utilized. Of the 213 seismic stations with recordings in the ground motion database, two had in-situ measurements of V S30 , 198 were assigned V S30 from the P-wave seismogram approach, and 14 were assigned V S30 from the geology-based proxy method using the statewide geologic maps of surface geology, as described in Zalachoris et al (2017). To assess the accuracy of both the P-wave seismogram V S30 estimates and geologybased V S30 proxies, we compare them with V S30 values derived from a series of in-situ V S measurements ( Figure 3) recently performed at seismic station locations in the Dallas-Fort Worth area using a combination of linear array active-source and two-dimensional array ambient-wavefield surface wave testing by Cox et al (2017).…”

“…Geology-based protocol for V S30 proxy assignment from Cox et al (2017) based on data fromZalachoris et al (2017) …”

Shallow elasticity structure from colocated pressure and seismic stations in the Piñon Flat Observatory and estimation of Vs30

“…Estimates for Vs30 have been made by various methods; drilling boreholes is the most direct approach but because of its high cost, non-invasive methods using surface seismic measurements, relying on active as well as passive seismic sources, are often used (e.g., Yong et al, 2016). There are other approaches such as particle motion analysis of body waves (e.g., Zalachoris et al, 2017;Park and Ishii, 2018). Our approach is also an alternative approach that requires colocated pressure and seismic sensors, relying on ambient seismic noise generated by atmospheric processes, primarily through surface pressure changes Wang, 2018, 2019).…”