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Earthquake Source Studies: Joint Inversion Of Broadband Seismological Data And Sar Interferograms

Domenico Giardini(1) and Paul Lundgren(2)

(1) ETH Zurich, Na, Na, Switzerland
(2) Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, United States


Earthquake source studies are generally implemented using different types of data: first, the local displacement field and accelerations (near-field data), and second, the wavefield generated by the earthquakes and recorded at teleseismic distances (far-field data). The main topic of our project (funded under AO3 #194, NASA SENH99-0168- 0042, ETHZ #0-20576-98),was the study of the rupture process of large earthquakes using a combination of (1) far-field broadband seismological data acquired by global seismological networks and (2) remote satellite measurements of the coseismic deformation fields (ERS1/2 satellites). The outcome of this work is the detailed appraisal of the space-time evolution of seismic ruptures in regions poorly instrumented with no proper near field equipments like GPS or strong motions stations. Through the study of different large events we show that the combination of the teleseismic and InSAR data sets in a joint inversion scheme is able to provide reliable assessments of slip distributions on faults. Seismological data alone cannot (or can only in very rare occasions) solve in a consistent manner for the source parameters of an event and resolve the trade off between rupture timing and slip location. Since the work of Massonet et al (1992) about the Landers 1992, California earthquake, the differential interferometry demonstrated its potential to map coseismic ground deformations on very large areas by constraining accurately the spatial complexity of fault and therefore limitating the trade off between rupture timing and slip location when jointly used with the teleseismic data. In this project, we carry out a joint analysis of seismological and InSAR data and assess their resolving power with synthetic data on different large earthquakes: the Mw= 7.7, Nazca (Peru), November 12, 1996, subduction event; the Mw= 7.1, Hector Mine (California), October 16, 1999, strike- slip event; the Mw= 7.5, Izmit, August 17, 1999, and Duzce (Turkey), September 12, 1999, strike-slip events. Improvements are further carried out by addition of other complementary data in the joint inversions: near-field strong motions, GPS data, complementary InSAR scenes and rupture offsets observations. From the different earthquakes source studies, we infer that the temporal and spatial complexities of a rupture can be resolved with better confidence when independent data sets are simultaneously inverted.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry