Fast approximate migration of ground penetrating radar using Kalman estimators and determination of the lithospheric structure of Lake Baikal, Russia

Oscar S Dena Ornelas, University of Texas at El Paso

Abstract

This dissertation is composed of two quite different studies. The first is related to the development of a migration algorithm for vertical incidence Ground Penetrating Radar (GPR) using the Kalman approach. The scope of any migration tool is to correct the position and to recover the true geometry of subsurface GPR targets. The advantage of using the Kalman approach is that the GPR records can be migrated at the same time when the data are being collected, avoiding further processing as is required by the available synthetic aperture algorithms for diffraction hyperbola collapse. The second part is a study of the lithosphere of the Lake Baikal, which is one of only a small number of Cenozoic continental rifts, the Baikal Rift Zone (BRZ) is a natural laboratory for understanding processes of rifting. Located in south-central Russia, the rift zone is known for Lake Baikal, a rift valley lake that contains 20% of the world's fresh water. Rifting in the region began about 25 Ma along the boundary between the Archean-Paleoproterozoic Siberian craton and the Early Paleozoic age Sayan-Baikal orogenic belt. Here we present a new velocity model for the structure of the crust along a 160-km transect in the north basin of Lake Baikal. The data, recorded in 1992, come from five 4-component ocean bottom seismometers (OBS) deployed at ca 40 km intervals. The source consisted of 2 air guns with a combined volume of 120 liters, that were fired at 240 m intervals along the transect. The data are of moderately good quality and are characterized by strong first arrivals to offsets of 40 km and a series of wide-angle reflections from interfaces in the crust, including the Moho. Travel times for both P- and S-wave arrivals from the crust were picked from the data. The velocity model, obtained through a combination of forward modeling and inversion, contains two shallow layers associated with basin sediments, a low velocity zone (LVZ) at 6 to 9 km depth, mid-crustal interfaces at ca. 12 and 22 km depth, a high velocity layer at ca. 33 km and Moho at ca. 40 km. The evidence for two distinct layers within the sedimentary section is consistent with geologic models that have proposed that there have been two distinct stages of rifting. Beneath the sedimentary layers, the crust is unusually fast with average velocities of 6.5 km/s at 5 km depth, increasing to 7.4 km/s at Moho. Possible origins for the low velocity zone are still being investigated. Joint analysis of the P- and S-wave models suggests that it has a Poisson's ratio greater than 0.3. The interface at 20 km may correspond to a detachment zone between 18 km and 22 km that has been proposed by previous workers. A ca. 7-km thick layer with velocities of 7.4 to 7.5 km/s forms the base of the crust. The Moho is essentially flat along the entire transect. The Low Velocity Zone in our model is consistent with an LVZ found in teleseismic and Deep Seismic Sounding (DSS) studies in the area. The mid-crustal reflector in our model coincides with a distinct band of reflectivity, suggestive of rifting, detected from DSS results. Seismic transects across and along the central basin of Lake Baikal detect a high velocity layer at the base of the crust similar to our model for the north basin.^

Subject Area

Geology|Geophysics

Recommended Citation

Dena Ornelas, Oscar S, "Fast approximate migration of ground penetrating radar using Kalman estimators and determination of the lithospheric structure of Lake Baikal, Russia" (2008). ETD Collection for University of Texas, El Paso. AAI3310706.
http://digitalcommons.utep.edu/dissertations/AAI3310706

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