Engineering ground motion characteristics and site characterization for earthquakes in Texas

The level of induced seismicity has been on an increase since 2009 in the states of Oklahoma, Kansas and Texas. Understanding the engineering characteristics of the ground motions from induced earthquakes in Central and Eastern North America (CENA) helps one to understand the potential for these earthquakes to cause damage. In particular, it is important to understand the ground shaking characteristics for moderate events that may cause infrastructure damage. Seismicity across the broader CENA region is also investigated for ground shaking due to the lesser frequency of moderate events in these states. Seven earthquakes of magnitude 5 and greater have happened in the CENA region in the preceding 70 years. This research studies the engineering characteristics of earthquake shaking from these events in terms of intensity, frequency content and duration from these seven earthquakes. In 2016, two moderate sized earthquakes occurred in Oklahoma, the Pawnee (M=5.8) and the Cushing (M=5.0) earthquakes. For the first time, earthquake motions within 10 km of an M~5 earthquake were recorded in CENA. In this study, all the earthquake motions recorded for these seven earthquakes within 400 km are analyzed in terms of: peak ground acceleration, spectral acceleration at 0.3 s and 1.0 s, peak ground velocity, Arias intensity, mean period, and duration. This study also examines the applicability of the P-wave seismogram method to estimate V [subscript S30] at stations in Texas and Oklahoma. The P-wave seismogram method was utilized to compute V [subscript S30] at 65 seismic stations and is combined with P-wave seismogram estimates from Zalachoris et al. (2017) to investigate V [subscript S30] across Texas, Oklahoma, and Kansas. The near-field recordings from the Cushing earthquake are particularly interesting, with peak ground accelerations as large as 0.25 to 0.6 g. However, these motions did not have significant energy at longer periods. The results from this study indicates the unique characteristics of near-field motions from potentially induced earthquakes in CENA (large PGA, smaller PGV, short duration), which influences the potential for damage to be induced during these events. Site-specific evaluation of the V [subscript S30] estimates from the P-wave seismogram approach with the help of limited in-situ measurements is also performed.