Deep Crustal Investigation of Central Oklahoma Using Local Earthquake Waveforms and Teleseismic Receiver Function Analysis

Session: Seismicity and Tectonics of Stable Continental Interiors
Type: Oral
Date: 4/30/2020
Time: 02:30 PM
Room: 240
Description: 

The midcontinent granite-rhyolite province evokes crucial questions about the tectonic processes that controlled the Proterozoic growth of the North American continental lithosphere. Present models for the evolution of the deeper crust are based on geochemical studies from drill cuttings and cores which only sample the uppermost crust, and also only at a few sites. Deep crustal seismic studies can help in understanding the deeper regional crustal structures. In this regard, Oklahoma presents a unique potential as induced seismicity in the past decade has led to installation of several temporary and permanent networks that captured a rich catalog of local and teleseismic events, which can be used for studying deeper crust in Oklahoma.

We apply common-midpoint (CMP) stacking and inversion techniques to Pg and PmP phases of induced earthquakes to obtain a 3-D velocity and Moho depth model for central Oklahoma. This technique allows us to investigate the crustal velocity structure up to ~40 km depth, which is a significant improvement to conventional local earthquake tomography. We use a total of 27,582 events recorded from 2010-2017 on 10 networks across Oklahoma to obtain localized 1D Pg travel-time curves, which are combined to get a 3D velocity model for the crust. We further derive a Moho depth model based on PmP phases.

In addition, 212 teleseismic events are used for receiver function analysis and H-k stacking to obtain a crustal thickness model and Vp/Vs ratios for central Oklahoma. We compare our velocity and Moho depth models with gravity and aeromagnetic data. We also compare observed crustal structures with the local seismicity patterns.

Our models show P-wave velocities for lower crust to be higher than 7.0 km/s and average Vp/Vs ratio greater than 1.8, which together are strong indicators of mafic lower crust. Moho depths vary between 40-48 km. We observe a generally homogeneous crust throughout entire central Oklahoma. Velocity variations are related to gravity and magnetic anomalies and are interpreted in the context of the assembly of different crustal blocks.

Presenting Author: Pranshu Ratre

Authors