Refining the shallow slip deficit

Geodetic slip inversions for three major (M_w > 7) strike-slip earthquakes (1992 Landers, 1999 Hector Mine and 2010 El Mayor–Cucapah) show a 15–60 per cent reduction in slip near the surface (depth < 2 km) relative to the slip at deeper depths (4–6 km). This significant difference between surface coseismic slip and slip at depth has been termed the shallow slip deficit (SSD). The large magnitude of this deficit has been an enigma since it cannot be explained by shallow creep during the interseismic period or by triggered slip from nearby earthquakes. One potential explanation for the SSD is that the previous geodetic inversions lack data coverage close to surface rupture such that the shallow portions of the slip models are poorly resolved and generally underestimated. In this study, we improve the static coseismic slip inversion for these three earthquakes, especially at shallow depths, by: (1) including data capturing the near-fault deformation from optical imagery and SAR azimuth offsets; (2) refining the interferometric synthetic aperture radar processing with non-boxcar phase filtering, model-dependent range corrections, more complete phase unwrapping by SNAPHU (Statistical Non-linear Approach for Phase Unwrapping) assuming a maximum discontinuity and an on-fault correlation mask; (3) using more detailed, geologically constrained fault geometries and (4) incorporating additional campaign global positioning system (GPS) data. The refined slip models result in much smaller SSDs of 3–19 per cent. We suspect that the remaining minor SSD for these earthquakes likely reflects a combination of our elastic model's inability to fully account for near-surface deformation, which will render our estimates of shallow slip minima, and potentially small amounts of interseismic fault creep or triggered slip, which could ‘make up’ a small percentages of the coseismic SSD during the interseismic period. Our results indicate that it is imperative that slip inversions include accurate measurements of near-fault surface deformation to reliably constrain spatial patterns of slip during major strike-slip earthquakes.

[1]  A. Treiman,et al.  Primary Surface Rupture Associated with the M w 7 . 1 16 October , 2002 .

[2]  Sergey V. Samsonov,et al.  InSAR imaging of displacement on flexural‐slip faults triggered by the 2013 Mw 6.6 Lake Grassmere earthquake, central New Zealand , 2015 .

[3]  Harry Fielding Reid,et al.  The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission ... , 2010 .

[4]  D. Sandwell,et al.  Phase gradient approach to stacking interferograms , 1998 .

[5]  John R. Rice,et al.  Dynamic motion of a single degree of freedom system following a rate and state dependent friction law , 1986 .

[6]  John H. Woodhouse,et al.  Determination of earthquake source parameters from waveform data for studies of global and regional seismicity , 1981 .

[7]  R. Langridge,et al.  Surface rupture displacement on the Greendale Fault during the Mw 7.1 Darfield (Canterbury) earthquake, New Zealand, and its impact on man-madestructures. , 2011 .

[8]  Jean-Philippe Avouac,et al.  Coseismic surface deformation from air photos: The Kickapoo step over in the 1992 Landers rupture , 2006 .

[9]  Robert Langridge,et al.  Lateral Offsets on Surveyed Cultural Features Resulting from the 1999 İzmit and Düzce Earthquakes, Turkey , 2002 .

[10]  Yuri Fialko,et al.  Shallow slip deficit due to large strike-slip earthquakes in dynamic rupture simulations with elasto-plastic off-fault response , 2011 .

[11]  G. King,et al.  Scaling of Fault Parameters for Continental Strike-Slip Earthquakes , 2007 .

[12]  J. Dolan,et al.  How well do surface slip measurements track slip at depth in large strike-slip earthquakes? The importance of fault structural maturity in controlling on-fault slip versus off-fault surface deformation , 2014 .

[13]  Y. Okada.  Internal deformation due to shear and tensile faults in a half-space , 1992, Bulletin of the Seismological Society of America.

[14]  L. Rivera,et al.  Coseismic Deformation from the 1999 Mw 7.1 Hector Mine, California, Earthquake as Inferred from InSAR and GPS Observations , 2002 .

[15]  John R. Rice,et al.  Crustal Earthquake Instability in Relation to the Depth Variation of Frictional Slip Properties , 1986 .

[16]  D. Sandwell,et al.  Static Rupture Model of the 2010 M7.2 El Mayor-Cucapah Earthquake from ALOS, ENVISAT, SPOT and GPS Data , 2010 .

[17]  D. Sandwell,et al.  A silent Mw 4.7 slip event of October 2006 on the Superstition Hills fault, southern California , 2009 .

[18]  Luis A. Dalguer,et al.  Numerical Study of Ground-Motion Differences between Buried-Rupturing and Surface-Rupturing Earthquakes , 2009 .

[19]  Duncan Carr Agnew,et al.  Coseismic Displacements from the Hector Mine, California, Earthquake: Results from Survey-Mode Global Positioning System Measurements , 2002 .

[20]  Sebastien Leprince,et al.  Quantifying near‐field and off‐fault deformation patterns of the 1992 Mw 7.3 Landers earthquake , 2015 .

[21]  H. Zebker,et al.  Fault Slip Distribution of the 1999 Mw 7.1 Hector Mine, California, Earthquake, Estimated from Satellite Radar and GPS Measurements , 2002 .

[22]  K. Feigl,et al.  Radar interferometric mapping of deformation in the year after the Landers earthquake , 1994, Nature.

[23]  William A. Bryant,et al.  Primary Surface Rupture Associated with the Mw 7.1 16 October 1999 Hector Mine Earthquake, San Bernardino County, California , 2002 .

[24]  K. Feigl,et al.  The displacement field of the Landers earthquake mapped by radar interferometry , 1993, Nature.

[25]  Yonghong Huang,et al.  Comparison of Several Multi-Look Processing Procedures in Insar Processing for ERS-1&2 Tandem Mode , 1997 .

[26]  A physical model of the effect of a shallow weak layer on strong ground motion for strike-slip ruptures , 1998 .

[27]  P. Rosen,et al.  Interferometric Synthetic Aperture Radar Geodesy , 2007 .

[28]  Penny J Johnes,et al.  AGU Fall Meeting Abstracts , 2013 .

[29]  Kenneth W. Hudnut,et al.  Detection of crustal deformation from the Landers earthquake sequence using continuous geodetic measurements , 1993, Nature.

[30]  Sebastien Leprince,et al.  Co-registration and correlation of aerial photographs for ground deformation measurements , 2009 .

[31]  Charles Werner,et al.  On the derivation of coseismic displacement fields using differential radar interferometry: The Landers earthquake , 1994 .

[32]  C. Thurber,et al.  Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California , 2009 .

[33]  David T. Sandwell,et al.  Coseismic slip model of the 2008 Wenchuan earthquake derived from joint inversion of interferometric synthetic aperture radar, GPS, and field data , 2010 .

[34]  Sébastien Leprince,et al.  Automatic and Precise Orthorectification, Coregistration, and Subpixel Correlation of Satellite Images, Application to Ground Deformation Measurements , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[35]  D. Agnew,et al.  The complete (3‐D) surface displacement field in the epicentral area of the 1999 MW7.1 Hector Mine Earthquake, California, from space geodetic observations , 2001 .

[36]  C. W. Chen,et al.  Two-dimensional phase unwrapping with use of statistical models for cost functions in nonlinear optimization. , 2001, Journal of the Optical Society of America. A, Optics, image science, and vision.

[37]  D. Sandwell,et al.  Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit , 2005, Nature.

[38]  Y. Fialko.  Probing the mechanical properties of seismically active crust with space geodesy: Study of the coseismic deformation due to the 1992 Mw7.3 Landers (southern California) earthquake , 2004 .