HR: 1340h
AN: S13B-1068    [Abstracts]
TI: Temporal variations of crustal characteristics
AU: * Liu, K H
EM: liu@ksu.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506 United States
AU: Gao, S S
EM: gao@ksu.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506 United States
AU: Nair, S K
EM: snair@ksu.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506 United States
AB: One of the most outstanding puzzles related to the formation and evolution of continental crust is whether crust formation processes have always been the same or whether they have changed with time. The most important piece of information to resolve this puzzle is to study the temporal variations of seismologically detectable properties of the continental crust. Previous seismological studies gave contradicting results. Using a modified version of the procedure of Zhu and Kanamori (2000), we have measured three parameters at GSN and GEOSCOPE stations for the purpose of characterizing the properties of the earth's continental crust of different ages. The parameters that we measured include a) crustal thickness (H); b) crustal Vp/Vs; and c) the amplitude of teleseismic P-to-S converted waves relative to that of the direct P-waves (R). For most of the stations, the number of hand-picked, high-quality receiver functions participated in the stacking is between 100 and 600. The stations are approximately evenly distributed over the continental areas of the earth. The stations are divided into three groups. Those in group one are on Cenozoic-Mesozoic orogenic zones, those in group two are on Paleozoic orogenic zones, and those in group three are on Precambrian platforms or shields. On average, the resulting R measurements are the largest at group one stations, and are the smallest at group three stations. The average H values are between 37-40 km for the three groups and are statistically indistinguishable. The mean Vp/Vs value is 1.81+-0.02, 1.77+-0.02, and 1.76+-0.01 for groups one, two, and three, respectively. One of the models to explain the observed reduction of Vp/Vs over age involves increasingly pervasive delamination of the mafic lower crust over time. Thermal events that caused the delamination might have reduced the sharpness and/or the flatness of the original Moho and consequently led to observed decrease of the amplitude of P-to-S converted phases with the age of the crust.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting