Preliminary Results of Rupture Process for 2003 December 26 Southeastern IRAN, Earthquake


Inversion was made using teleseismic data (provided by IRIS-DMC)

On December 26, 2003 (GMT), a destructive earthquake (Ms 6.5) struck southeastern Iran. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 16 stations were selected from the viewpoint of good coverage, and used in the waveform inversion with ABIC (Fukahata et al., 2003; Yagi et al., 2003).

Result

The seismic moment Mo = 6.8 x 10**18 Nm (Mw 6.5);
The source duration T = 15 s;
(strike, dip, rake) = (173, 63, 159.6)
Hypocenter: (Lat. = 28.990N, Lon. = 58.288E, depth = 10 km) [Fix].
[The epicenter of the main-shock was determined by USGS]
Variance: (obs-cal)**2/obs**2 = 0.47105
Maximum slip = 1.2(m)
Maximum stress drop = 6.1 MPa

The rupture mainly propagated about 25 km to the south from hypocenter. The rupture may extend to surface of the earth. Three asperities (large slip areas) are identified. The maximum dislocation is about 1.2 m 5km east from hypocenter. The strong ground motion should extend to south direction due to the effect of rupture propagation.

Note: Since I used the teleseismic body wave, the resolution of space is not so good. The maximum dislocation and fault area will be revised using the near-field data.

(Yagi, IISEE, BRI, 2003)


Distribution of fault-slip



Figure : (upper left) Focal mechanism; (upper right) Total moment-rate function; (lower) Distribution of coseismic slip. Star indicates the location of the initial break.

Stress change on the fault plane due to fault-slip



Figure : Distribution of shear stress change due to the mainshock. Blue and red areas indicate the zones of stress decrease and increase, respectively. Star indicates the location of the initial break.

Map View



Figure: Hypocenter of the main-shock determined by USGS. Blue lines represent the extent of the fault plane used in our inversion.

Waveform comparison


Figure : Comparison of the observed waveform (Black) with the calculated waveform (Red). The numbers below the station code indicate maximum amplitude in microns. The start time of the traces is lined-up at 10 (s) before the P-wave arrival.



Figure : Teleseismic stations used in inversion. The star represents the epicenter of the main-shock.

Reference

Fukahata, Y., A. Nishitani and M. Matsu'ura, Geodetic data inversion using ABIC to estimate slip history during one earthquake cycle with viscoelastic slip-response functions, Geophys. J. Int., accepted 2003a.

Fukahata, Y., Y. Yagi, and M. Matsu'ura, Waveform inversion for seismic source processes using ABIC with two sorts of prior constraints: Comparison between proper and improper formulations, GRL, 30, 10.1029/2002GL016293, 2003b.

Yagi, Yagi ; T. Mikumo; J. Pacheco, Source rupture process of the Tecoman, Colima, Mexico earthquake of January 22, 2003, determined by joint inversion of teleseismic body wave and near-field data (PDF), submited to Bull. Seism. Soc. Am., 2003.


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If you have questions, please send to yagi@kenken.go.jp.

Last Updated: December 27, 2003