EIC Seismological Note No. 138 Aug.10, 2003

Preliminary Results of Teleseismic Body Wave Analysis
Source Rupture Process of the Scotia Sea
earthquake (Ms 7.5) of August 4, 2003
< Hypocenter information >

QED (quick epicenter determination) information due to USGS is:

Origin Time  04:37:20 (UT)
Epicenter    60.56 S, 43.59 W
Depth        shallow
Ms           7.5

< Data and Analysis >

  16 vertical components of P-wave data and 3 SH data at IRIS stations
were retrieved and converted into ground displacement.  The waveforms
suggest very complicated rupture process with mechanism change.
At first, we derived two subevents of point dislocations. The introductory
subevent reveals a strike-slip with a considerable normal fault component,
while a major subevent is a nearly pure strike-slip event (Fig. 0).
Next, with a fixed fault plane as inferred from the overall mechanism,
we inverted a spatio-temporal distribution of fault slip.

< Results >

   The results are shown in Fig. 1.  Main source parameters
derived are as follows:

   Overall mechanism: (strike, dip, slip) = (110, 64, -13)
   Seismic moment  Mo = 2.0 x10**20 Nm (Mw = 7.5)
   Source duration T = 20 s
   Centroid depth H = 20 km
   Rupture area  S = 50 km x 25 km
   Maximum dislocation Dmax = 6.2 m
   Averaged dislocation Da = 2.7 m
   Averaged stress drop = 11 MPa

                                      (M. Kikuchi and Y. Yamanaka)