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Romero-de la Cruz, Oscar, 2011

Seismological studies in south-central Alaska and northern Mexico

Bibliographic Reference

Romero-de la Cruz, Oscar, 2011, Seismological studies in south-central Alaska and northern Mexico: University of Texas, El Paso, Ph.D. dissertation, xiv, 105 p.,illust., maps.

Abstract

The work in this study is focused on two different areas, south-central Alaska and northern Mexico. In the first study area, I calculated dynamic stress drops for moderate-sized earthquakes and performed receiver function analyses. The goal of the stress drop studies was to determine if events occurring in the more strongly coupled portion of the subducting slab have higher stress drops. My results show that higher stress drops correspond to the locked and strongly coupled region in Prince William Sound, and lower stress drops are associated with the Cook Inlet region, a zone of relaxation of the plate interface. The receiver function analysis focused on data from an isolated broadband station on the Kenai Peninsula that may be located near the edge of the strongly coupled portion of the Yakutat microplate. The station recorded global teleseismic events of M >5.5 for three different periods, achieving a total recording of ~9 months. I used these data to determine the crustal structure from the P to S converted phases. The best match to data shows a thickness of 34 km and a Vp/Vs ratio of 1.45 just under the station, but three other results from different directions obtained values of 28 km and a ratio of 2.3 to the south of the station, 30 km and a ratio of 1.98 southwest of the station, and 32 km and a ratio of 1.63 eastward from the station. This would suggest the presence of a mantle wedge beneath the study area. In the second study area, northern Mexico, I obtained a crustal velocity model by means of the Joint Hypocenter Determination inversion technique using microseismicity and mining blasts in the region as sources. The final model shows the moho depth at 30 km and the upper-lower crust boundary at 21 km. The inclusion of a transition layer at 12 km allowed better adjustment than preliminary starting model of Harder and Keller. The new locations of the epicenters maintain the alignment to the Pitaycachi fault and the mining blasts clusters converge better to the mining locations.

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