Thesis Defense Announcement

Chloe Glover

Advisor: Charles Langston

Transmission and Reflection Imaging Of Stratigraphy From Passive Array Data

ABSTRACT:.The Incorporated Research Institutions in Seismology (IRIS) Consortium conducted a community wavefield experiment in Oklahoma in the summer of 2016. Seismograms from five local events recorded by a 3-line array of short-period stations were used to identify phase conversions in the upper crust. We observed large Sp conversions that dominate the P-wave coda and large S-waves; this indicates structure affects the P-wave much less than other phases. Sp conversion times were calculated using a continuous velocity model and geometrical ray theory to solve for P- and S-wave travel times. The earthquake data from each event was separated 3 arrays to convert array seismograms into depth images. Testing was completed by re-processing data assuming different earthquake source depths and using altered velocity models. Two event depths were adjusted as a result of testing. A major Sp phase conversion was identified at 0.5 km, with several other large conversions evident between 1.5 and 2.5 km depth across all profiles and events. The 0.5 km depth conversion correlates to a discontinuity that represents the base of the Tertiary sedimentary basin/top of the Permian red-bedded sand stones and shales. The various conversions that are present between 1.5- and 2.5-kilometers depth correspond to the top of the Pre-Cambrian basement and agree with measured basement depths extracted from historic well data in the region. Synthetic seismograms were used to validate the structural imaging results and acceptably produced conversions at 0.5 and 1.5-2.5 km depth for a hypothetical strike-slip event at 4.5 km depth for 20 stations in a 4 km long array with 200-meter receiver spacing.