Jean-Philippe Avouac photoJean-Philippe Avouac Professor of Geology:Director of the Tectonics Observatory:CaltechCaltech logo

Research

From Earthquakes to Orogenesis, the Central range of Taiwan.

Taiwan is an exceptional area to investigate seismotectonic and orogenic processes because of very rapid rates of deformation and recurrent large earthquakes associated with the ongoing collision between the Luzon arc and the eastern continental margin of China [e.g. Malavieille et al., 2002] (Figure 1).

img002 (From Angelier)

Much insight can be gained in particular from studying the western flank of the Central Range which is a classical example of a fold and thrust belt [e.g., Suppe and Jamison, 1979], across which thrust faulting accommodates as much as 4cm/yr of shortening according to GPS measurements [Yu et al., 1997; Yu et al., 2001].   Several faults seem to be active including the Chelungpu that ramps to the surface along the front of the range and the Changhua fault which is a blind fault below the Pakuashan anticline in the piedmont (Figure 2).

img004 (Dominguez et al., 2003)

The Mw 7.6 Chichi earthquake in 1999 broke a shallow portion of the Chelungpu fault [e.g., Kao and Chen 2000]. Ground displacements during that earthquakes could be measured from GPS [Yu et al., 2001] but also from  SPOT images [Dominguez et al., 2003] (Figure 3).

img006

                                                                                                                                                            (Dominguez et al., 2003)

Modeling of GPS measurements show that this fault was previously fully locked over a distance of about 40 km from the surface to a depth where it also roots to some sub-horizontal aseismic ductile shear zone [Dominguez et al., 2003] (Figure 4).  If we compare coseismic displacements with interseismic displacements, the recurrence interval of earthquakes similar to the Chichi events can be estimated to between 150 and 250 years. This estimate assumes that all the shortening across the western flank of the Central range is taken up by co-seismic slip on the range bounding thrust faults and that the shortening rate measured over the few years before the Chichi earthquake is representative of the average shortening rate over the whole interseismic period. Both assumptions might be questioned.

img008        (Dominguez et al., 2003)

The earthquake was followed by some afterslip downdip of the rupture [Hsu et al., 2002], probably in a transition zone between the domain of unstable frictional sliding and the zone of ductile flow at depth. This process could be modeled from the response to the co-seismic stress change of the stable sliding portion of the fault [Perfettini and Avouac, submitted]. This model predicts an Omori (1/t) decay law for both the geodetic data and the aftershocks, a model that could be tested successfully. 

Probably, on the longer term, the geodetic measurements will also show evidence for postseismic viscous relaxation putting additional constraints on  rheological parameters. The orogenic process of the long term must result from cumulated co-seismic and interseismic deformation, but the detail of the kinematics by which material is accreted to the orogenic wedge (by frontal accretion or underplating) remains unclear.

Our project aims more particularly at

-        determining how deformation is partitioned on the various parallel thrust faults (mainly the Changhua and Chelungpu faults),

-        comparing deformation resulting from recurrent earthquakes on these faults with the long term orogenic processes,

-        assessing the coupling between the thermal structure, erosion and tectonic deformation.

-        assessing the thermal control on crustal rheology, in particular the changes from unstable frictional sliding, to stable frictional sliding, and ultimately to ductile flow at depth.

Our approach combines morphotectonics investigations, structural geology, thermometric investigations from Raman Microspetroscopy on Carbonaceaous Matter (RSCM) [Beyssac et al., 2002a, 2002b], thermal modeling, and mechanical modeling.

My main collaborators on this project are :

Martine Simoes, PhD student at Caltech and ENS, Paris

Yu Gau Chen from National Taiwan University, Taipei

Yu-Chang Chan from Academia Sinica, Taipei

Olivier Beyssac from CNRS, ENS, Paris

Stéphane Dominguez at CNRS, Montpellier

References

Beyssac, O., Rouzaud J.N., Goffé B., Brunet F. and C. Chopin Graphitization in high-pressure, low-temperature metamorphic gradient: a HRTEM and Raman microspectroscopy study. Contributions to Mineralogy and Petrology, 143, 19-31, 2002a.

Beyssac O., Goffé B., Chopin, C. and J.N. Rouzaud, Raman spectra of carbonaceous material from metasediments: a new geothermometer. Journal of Metamorphic Geology, 20, 859-871, 2002b.

Dominguez S., J.P. Avouac, R. Michel, Horizontal co-seismic deformation of the 1999 Chi-Chi earthquake measured from SPOT satellite images: implications for the seismic cycle along the western foothills of Central Taiwan, J. Geophys. Res., 108, 2, 1029/2001JB00482, 2003.

Hsu, Y. J., N. Bechor, P., Segall, S.-B. Yu, L.C. Kuo and K.F. Ma, Rapid afterslip following the 1999 Chi-Chi, Taiwan earthquake, Geophys. Res. Lett., 29, 10.1029/2002GL014967, 2002.

Kao H. and Chen W.-P., The Chi-Chi earthquake sequence: Active out-of-sequence thrust faulting in Taiwan, Science, 288, 2346-2349, 2000.

Ji, C., T. Helmberger, T. Song, K. Ma and D. Wald, Slip distribution and tectonic implication of the 1999 Chi-Chi earthquake, Geophys. Res. Lett., 28, 4379-4382, 2001.

Malaveille, J., S. Lallemand, S. Dominguez, A. Deschamp, Arc-Continent collision in Taiwan: Marine observations and tectonic evolution, Geol. Soc. Am., Sp. Pap. 358, 189-213, 2002.

Yu, S. B., Chen, H. Y., and Kuo, L. C., Velocity field of GPS stations in the Taiwan area, Tectonophysics, 274, 41-59, 1997.

Yu, S. B., L. C., Kuo, Y.J., Hsu, H. H., Su, C. C. Liu, C. S., Huo, J. F. Lee, T. C., Lai, C. L., Liu, T. F. Tseng, C. S., Tsai, and T. C. Shin, Preseismic deformation and coseismic displacements associated with the 1999 Chi-Chi, Taiwan earthquake, Bull. Soc. Am., 91, 995-1012, 2001.

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