Where are all the Pawnee Area Earthquakes Originating
Authors: Jake Walter, Ph.D., OGS, Priyank Jaiswal, Ph.D., OSU, Bob Springman, GTSeis
Presenter: Bob Springman, GTSeis
On September 3rd, 2016 the largest earthquake in Oklahoma recorded history was felt across most of the Mid-Continent region, as reported by Channel 9 news of Oklahoma City. The location of the epicenter was quickly determined by the U.S.G.S and O.G.S. Since then, hundreds of seismometers have recorded continued earthquake activity. Over 1,200 epicenters have been recorded in the Pawnee Epicenter Area accurately measuring the magnitude, location and depth of each epicenter.
Many man hours, efforts and money has been spent attempting to identify the origin of these epicenters. From analysis of the seismicity data recorded, opinions of the origins and trends of the epicenters has been as varied as the epicenters themselves. We built a velocity model by integrating a sonic log from the surface to the top of the Arbuckle with a model estimating velocities below the Arbuckle to estimate time to depth conversions to 64,000 feet.
An OGS relocated earthquake dataset, suggests that less than 5% of the epicenters occurred above 8,000 feet. Geologic information below 8,000 feet in the Pawnee area is unknown Precambrian sub-metarhyolite. Therefore, 95% of the epicenters are measured 8,000 feet to 32,323 feet originating below the top of the known metarhyolite, probably in Proterozoic Eon age.
With the combined data, effort and work by the Oklahoma Geological Survey, Oklahoma State University and GTSeis along with the generous donation of 3D seismic data images from Silverthorne Seismic, the subsurface origin of each epicenter has been identified. The origin and cause of 95% of the epicenters in the Pawnee area correlate to deep, probably Proterozoic fault plate movements. Much work needs to be done in the future to better define and understand the cause and trends of each plate movement epicenter in the Pawnee area.
Robert Springman is a General Manager of GTSeis with 50 years of experience in geophysical imaging. His work started in Houston with Geophysical Services, Inc. doing seismic data processing and then interpretation. After leaving GSI he continued his career in seismic interpretation with both large oil and gas companies and small independents in positions as geophysicist, geophysical manager, chief geophysicist and independent geophysical consultant. Areas of experience have been in the G.O.M., Rockies, Mid-Continent, North Texas and various international exploration areas. His work has led to discoveries of many MMBO and hundreds of BCFG. Numerous publications, courses and presentations in geophysical imaging have been made to AAPG conventions, SEG, geophysical society and geological society meetings. He has served five years as the continuing education chair for the GSOC and served in officer positions of the GSOC through president. Presently Vice President of the GSOC and invited instructor of geophysics interpretation at Oklahoma State University. He is a life time member of the GSOC, active member of the DGS and OCGS and emeritus member of the SEG.
Bob earned a B.S. degree in Geology and Mathematics from Oklahoma State University in 1973.