Imaging the Deep Crustal Structure of Central Oklahoma Using Stacking and Inversion of Local Earthquake Waveforms. Issue 5 (22nd May 2021)

• Record Type: Journal Article
• Authors: Ratre, Pranshu; Behm, Michael
• Is Part Of: Journal of geophysical research. Volume 126:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-22
• Subjects: crustal structure of Oklahoma -- Mesoproterozoic -- seismic tomography -- southern Granite‐Rhyolite province; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB021368
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: The southern Granite‐Rhyolite province (SGRP) contains a comprehensive record of lithospheric evolution in North America. During the last decade, increased seismicity along with improved seismic monitoring in Oklahoma provided a rich catalog of local earthquakes. The source‐receiver geometry of this data set is well posed to illuminate the middle and lower crust through long offset recordings of the Pg phase. We present a 3‐D P‐wave velocity model for central and northern Oklahoma developed through a non‐standard processing scheme applied to local earthquake waveforms recorded from 2010 to 2017, focusing on the deeper crust. We employed common mid‐point sorting, stacking, and inversion of Pg phases which resulted in a set of localized velocity‐depth functions up to depths of 40 km. Using this methodology, we significantly increased the S/N ratio for far offset (∼200 km) local earthquake waveforms which led to the increase in depth of investigation in the final 3‐D velocity model. We find high velocity (>7 km/s) lower crust throughout the investigated area which suggests a mafic lower crust. The high velocities support previously established models which state that the lower crust of the SGRP was derived from melting of older crust. We further relate shallow and middle crustal velocity anomalies to other data sets such as gravimetric and magnetic anomalies, and the spatial distribution of earthquakes. We do not find clear evidence for the existence of the Midcontinent Rift in northern Oklahoma. Plain Language Summary: To understand how the crust in Oklahoma was created we require information from the deepest, oldest part of the crust. Waves generated by earthquakes can be used to image the Earth's crust. The farther these waves travel, more noise is added to the data. Our technique minimizes the noise and enhances the signal observed even at stations that are greater than 200 km away from the earthquake source. This helps in deriving rock properties for the deepest part of the Earth's crust. Oklahoma has recently seen an exponential increase in the number of earthquakes due to oil and gas production activities. Spatially, they cover a large area in central Oklahoma, thus providing dense subsurface information in this region. We use these earthquakes and apply our technique to derive velocities of the Primary waves (P‐waves) within the crust. We observe velocity variations that indicate intrusive structures in the upper crust. We also observe high P‐wave velocities for the lower crust which indicates that the crust is composed of high‐density material. Our 3‐D P‐wave velocity model provides insights into the nature of the crust and also gives a deeper and more detailed picture of the regional crustal structures in Oklahoma. Key Points: A 3‐D Pg wave velocity model in central Oklahoma is developed, up to depth of 40 km High velocity (Vp > 7 km/s) lower crust suggests a mafic lower crust High Vp anomalies found in the upper‐middle crust, but lack clear signs for a structure comparable to the Midcontinent Rift north of Oklahoma