HR: 09:30h
AN: S31B-07    [PDF]
TI: Examination of systematic mislocation of south sandwich islands earthquakes from station pairs: Implications for inner core rotation
AU: * Sun, X
EM: xsun@uiuc.edu
AF: Geology Dept., Univ. of Illinois at Urbana-Champaign, 245 N.H.B., 1301 W. Green st, Urbana, IL 61801 United States
AU: Song, X
EM: xsong@uiuc.edu
AF: Geology Dept., Univ. of Illinois at Urbana-Champaign, 245 N.H.B., 1301 W. Green st, Urbana, IL 61801 United States
AB: One of the most robust observations for the inner core rotation is that the differential PKP BC-DF travel times from South Sandwich Islands (SSI) earthquakes to College, Alaska (and some other stations in Alaska) have increased systematically over the past 50 years. The time shift in the differential time residuals is about 0.12 s per decade. However, the time-dependence was questioned because of possible systematic earthquake mislocation. Here we examine about 40 years of P arrival times between pairs of stations. We examine how the difference in P residuals of one station at similar azimuth as the path from SSI earthquakes to Alaska and the other station at the opposite azimuth changes with time. Because the differential horizontal slowness between the P arrival times of the pairs is 10 to 20 times that of the differential BC-DF times, mislocation would cause a time shift of the differential P times an order of magnitude larger than that of BC-DF times. Our preliminary results from time picks of earthquake bulletins suggest that most of the station pairs have a a very small increase of differential P residuals with time and some station pairs have a decrease of residuals with time. After removing all the means of the residuals of different station pairs, the combined data suggest an increase of 0.1 to 0.2 s per decade. Assuming the time shift is caused by mislocation, the corresponding time shift for the differential BC-DF times at Alaska stations would be less than 0.02 s per decade, which is much less than the observed time shift of the BC-DF times. We have also collected P waveforms of a selected few stations. Results from the precise time picks of these stations will be presented.
DE: 7207 Core and mantle
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting