9:15 AM - 9:30 AM
[SSS13-26] ICDP DSeis 10: Near-field Observations for the M5.5 Orkney, South Africa Earthquake
Keywords:Orkney earthquake, South Africa, slip inverstion
The waveforms show that there is a small foreshock (about M1.8) located 1.6 km south of the mainshock hypocenter and at 0.6 sec before the mainshock. There is no evidence of any unusual character of the foreshock, or any significant deformation between the foreshock and mainshock.
Using lower frequency (<2.0 hz) data, the nearfield waveforms can be modeled using a finite fault slip inversion. The results show a slip distribution with two main patches of larger slip, which are located a few kilometers to the north and to the south of the hypocenter. The area of the fault plane is relatively large for a M5 earthquake and this gives a rather small static stress drop.