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>Return to Research
Co-seismic, post-seismic, and inter-seismic deformation in strike slip systems
Large strike-slip fault systems are frequently ideally suited for study using InSAR since they are usually subareal and experience large displacement very close to the surface. Our observational studies currently focus on the 1992 Landers (CA), 1999 Hector Mine (CA), 1997 Manyi (Tibet), 1995 Kobe (Japan) earthquakes. We have thus far investigated the 3D co-seismic displacement field at the surface (10), the on-fault distribution of co-seismic slip (15), the average depth distribution of co-seismic slip (15, 31), and implications for the long term strain budget in the shallow crust (15, 16, 31).We are now struggling with the most appropriate ways to combine geodetic and seismic constraints on our slip models, and attempting to isolating and understanding co-seismic deformation that occurs nearby but off the primary faults.
There are several technical issues to be dealt with in this effort. From the perspective of InSAR data, we need to figure out how to distill the relevant constraints from O (107) pixels in a computationally efficient manner while attempting to keep track of the error structure of the data (29). Given any kind of geodetic data, we need to consider optimal approaches to inferring the distribution of co-seismic and post-seismic displacements on and off the fault (S1).Post-seismic observations provide insight into the inelastic character of the lithosphere. Such processes are sensitive to both the co-seismic kick and the state of stress present before the earthquake. The former sensitivity is a primary motivation for spending so much effort on understanding distribution of co-seismic (including the model errors and resolution). The latter sensitivity motivated us to consider the behavior of long sequences of earthquakes (28). In a semi-analytical 1D spring-dashpot-slider model, we found that in the presence of system noise, the historesis inherent in visco-elastic systems could result in temporal clustering of large earthquakes. The tendency to cluster increases as the loading rate drops, the size of the characteristic earthquake increases, and the Maxwell relaxation time decreases. This is simply described using a non-dimensional parameter, W, which we call the Wallace Number. In the presence of noise, W>1 is associated with temporally clustered earthquake time series. We are now validating validating these conclusions for more realistic 2D systems using a finite element modelling approach. This effort will also permit a more direct comparison with real-world examples.
S1 Improving Inferred Models of Distributed Fault Slip, R. B. Lohman, M. Simons, Geophys. J. Int., submitted, 2004.
31Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit , Fialko,Y., Sandwell, D., Simons, M. & Rosen, P., Nature, Vol 435, 19 May 2005, doi:10.1038/nature03425. [PDF]
29 Some thoughts on the use of InSAR data to constrain models of surface deformation, R. B. Lohman, M. Simons, G-cubed, Vol. 6, No. 1, Q01007, doi:10.1029/2004GC000841, Jan. 25, 2005. [PDF]
28 Temporal clustering of major earthquakes along individual faults due to post-seismic reloading, S. Kenner, M. Simons, Geophys. J. Int., 2005, 160, 179-194. [PDF]
16 Deformation on nearby faults induced by the 1999 Hector Mine Earthquake, Fialko, Y., D. Sandwell, D. Agnew, M. Simons, et al, Science, 297, 1858-1862, 2002. [PDF]
15 Coseismic Deformation from the 1999 Mw 7.1 Hector Mine, California, Earthquake as Inferred from InSAR and GPS Observations, M. Simons, Y. Fialko, and L. Rivera, Bull. Seismol. Soc. Am., 92, 1390-1402, 2002. [PDF]
10 The complete (3-D) surface displacement field in the epicentral area of the 1999 Mw7.1 Hector Mine earthquake, California, from space geodetic observations, Fialko, Y., M. Simons, and D. Agnew, Geophys. Res. Lett., 28, 3063-3066, 2001. [PDF]
5 Preliminary Report on the 10/16/99 M7.1 Hector Mine, California earthquake, Scientists of the USGS, SCEC, and CDMG, Seismol. Res. Lett., 71, 11-23, 2000.
Mark Simons' Paper Collection: Entire paper including figures are all made available online (within the bounds of copyright restrictions).
