JOINT INVERSION OF GEODETIC AND SEISMIC SLIP MODELS FOR THE APRIL 04, 2010 EL MAYOR-CUCAPAH EARTHQUAKE

We use teleseismic records together with measurements of static ground displacements at GPS stations and derived from optical and InSAR satellite images, to derive a finite source kinematic model of the April 4, 2010, the Mw7.2 El Mayor-Cucapah (Baja, California) earthquake. The sub-pixel correlation of optical SPOT 2.5 m panchromatic images indicates that the rupture broke the surface for over 55km to the northwest of the epicenter with an average of 2.5m right-lateral slip. Southeast of the epicenter, the InSAR data reveals offsets of up to a meter over even a larger length. We modeled the teleseismic waveforms using these constraints and the co-seismic displacements measured at a number of California GPS stations. The seismic records show that the earthquake released a total seismic moment of M₀=7.9*10²⁶ dyne*cm(Mw7.2) in the first 40 seconds of rupture. The inversion of the first 15 seconds of teleseismic body wave shows that the quake started as a normal event consistent with a mechanism of 345°/45°/-80° (strike/dip/rake) and a moment of at least Mw6.3. The earthquake then paused and continued on the main N310°E striking fault strand producing a bilateral transtensional rupture. Most of the slip to the north of the epicenter required to match the optical, InSAR and GPS observations seems to have been coseismic. By contrast, our preliminary results suggest that some significant fraction of the slip on the fault strand south of the epicenter was aseismic.

Additional co-authors on this abstract: Rich Briggs, Ken Hudnut, and Sinan Akciz