Colima Earthquake

Preliminary Results of Rupture Process for January 22, 2003 Colima, Mexico, Earthquake

Result of Joint inversion

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), by Yagi, Yagi ; T. Mikumo; J. Pacheco
submited to Bull. Seism. Soc. Am., 2003.

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

On January 22, 2003, a large thrust earthquake (Mw = 7.4) occurred in Colima, Mexico, where the Cocos plate subducts beneath the North American Plate. I retrieved teleseismic body waves (P-waves) data recorded at IRIS-dmc stations via Internet. 12 stations were used in the waveform inversion with ABIC (Fukahata et al., 2002).
I determined a focal mechanism using teleseismic body wave.
(strike, dip, rake) = (300, 20, 93)
This focal mechanism is consistent with IISEE CMT solution determined by Dr. Hara and release of stress buildup on the inter-plate boundary.

Result

The seismic moment Mo = 1.45 x 10**20 Nm (Mw 7.4);
The source duration T = 20 s;
Hypocenter: (Lat = 18.625 N, Long = 104.125 W, depth= 20 km).
[The epicenter of the main-shock was determined by RESCO (local seismic network operated by Colima University)]

The source process is characterized by a unilateral rupture propagation. The rupture mainly propagated 40 km to the Northwest. The maximum dislocation is about 3.0 m at about 15 km northwest from hypocenter. The rupture area coincides with the seismic gap (G.E.G.). This result is consistent with the aftershock distribution determined by UNAM.

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, 2003)

Distribution of fault-slip

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

Map View

Figure: Hypocenter of the main-shock determined by RESCO (local seismic network operated by Colima University). Blue lines represent the extent of the fault plane used in our inversion.

Snapshots

Figure : Snapshots of cumulative dislocation.

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., Y. Yagi, and M. Matsu'ura, 2002, Waveform inversion for seismic source processes using ABIC with two sorts of prior constraints: Comparison between proper and improper formulations, submitted to GRL. PDF File

Links

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