Nov. 04, 2002 (Rev. 02/11/05)

Source rupture processes of the central Alaska earthquake
of Nov. 3, 2002, inferred from teleseismic body waves
(+ the 10/23 M6.7 event)
by M. Kikuchi, and Y. Yamanaka (ERI, Univ. Tokyo)

Broadband records at teleseismic distances were retrieved from IRIS Web site: WILBER-II. The waveforms are very complex, indicating a multiple shock nature of this earthquake source process.


We first applied the iterative deconvolution by Kikuchi and Kanamori (1991), where the source process is modeled as a sequence of discrete subevents with variable mechanisms. Then two subevents were derived: the one for initial 30 s and the other for a later 60 s. The mechanism is completely different: the first event is a reverse-fault striking NE-SW and the second is a right lateral strike-slip (Fig.1). The source parameters for the reverse-fault are: (strike, dip, rake) = (227, 40, 99); the source duration = 16s; Mo = 4.6x10**19 Nm. Note that even an introductory rupture has a size of Mw 7.0.
The centroid of the main event is located about 180 km east to the initial break (63.74N, 147.69W after QED). For the rupture process of the main strike-slip, we constructed the grid scheme on the fault plane to determine the spatio-temporal distribution of the moment release. The results are shown in Fig.2 (moment-rate, waveform comparison etc.) and Fig.3 (map view: slip distribution projected on a horizontal plane).
A strike-slip rupture started near the epicentral area and rapidly extended to the east with 3 km/s. The total length exceeded 200 km. The source parameters for the major strike-slip event are as follows:

centroid depthh0=15 km
(strike, dip, rake) (294, 86, 161)
seismic moment Mo = 7.8x10**20 Nm (Mw=7.9)
source duration T = 70 s
fault area S = 200kmx30km
dislocation (Maximum) Dmax = 12 m
(averaged) Da = 4.3 mĦĦ(rigidity = 30GPa)
stress drop (averaged) DELTA sigma = 4.2 MPa

Teleseismic analysis for the M6.7 shock of Oct. 23, 2002 is shown in Fig.4 (moment-rate, waveform comparison etc.) The epicenter is referred to USGS's: (63.62N,148.04W). The main source parameters obtained are:
Mo=1.2x10**19 Nm (Mw 6.7); (strike,dip,rake)=(265,80,179); Fault area S=30km x 10km; Dmax=1.7m Da=1.4m; stress drop=6.0MPa.