Case Studies of Seismic Tomography and Earthquake Location in a Regional Context

We present three case studies of traveltime tomography applied to regional imaging of the earth's crust and upper mantle. The first case study investigates the imaging of Poisson's ratio using measurements of compressional and shear wave traveltimes. Inversions schemes that jointly fit both types of traveltime data and that selectively damp the compressional to shear wave velocity ratio are shown to be very effective. The second case study focuses on the ability of joint inversions of crustal and Moho-reflected wave traveltimes to image both crustal velocity structure and Moho topography. The ability of this kind of tomography to distinguish Moho topography and lower crustal heterogeneity is shown to be poor. The third case study examines the ability of teleseismic tomography to determine the shape of a mantle plume. A new test for departures from an axial shape is proposed and tested. We also present a case study of earthquake location, that compares locations made with traditional P and S wave traveltimes to those based on differential P wave traveltimes (that is, the double-difference method). The underlying tomography software, raytrace3d that is used in this study and which is publicly and freely available is described, and the technical elements of traveltime tomography are fully documented in an appendix.

[1]  W. Menke,et al.  Compressional and shear velocity structure of the lithosphere in northern Iceland , 1998, Bulletin of the Seismological Society of America.

[2]  P. Shaw.  Age variations of oceanic crust Poisson's ratio : inversion and a porosity evolution model , 1994 .

[3]  Walter H. F. Smith,et al.  Free software helps map and display data , 1991 .

[4]  Arthur S. Ritchie,et al.  Handbook of Physical Constants , 1967 .

[5]  P. Einarsson,et al.  Seismic structure of Iceland along RRISP-profile I , 1980 .

[6]  G. Abers,et al.  Three‐dimensional inversion of regional P and S arrival times in the East Aleutians and sources of subduction zone gravity highs , 1994 .

[7]  E. Husebye,et al.  Seismic image of the hypothesized Icelandic hot spot , 1983 .

[8]  W. J. Morgan,et al.  The seismic anomaly beneath Iceland extends down to the mantle transition zone and no deeper , 2000 .

[9]  Keiiti Aki,et al.  Three-dimensional seismic structure of the lithosphere under Montana Lasa , 1976, Bulletin of the Seismological Society of America.

[10]  J.B.W..  Seismological Tables , 1916, Nature.

[11]  Joab R Winkler,et al.  Numerical recipes in C: The art of scientific computing, second edition , 1993 .

[12]  E. Humphreys,et al.  Upper mantle P wave velocity structure of the eastern Snake River Plain and its relationship to geodynamic models of the region , 1997 .

[13]  Sigurdur Th. Rognvaldsson,et al.  Absolute and relative locations of similar events with application to microearthquakes in southern Iceland , 1995 .

[14]  R. Carmichael.  CRC handbook of physical properties of rocks , 1982 .

[15]  B. Kennet.  Iaspei 1991 Seismological Tables , 1991 .

[16]  F. Waldhauser,et al.  A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California , 2000 .

[17]  William H. Press,et al.  Numerical recipes in C. The art of scientific computing , 1987 .

[18]  Colin A. Zelt,et al.  Three‐dimensional seismic refraction tomography: A comparison of two methods applied to data from the Faeroe Basin , 1998 .

[19]  Sean C. Solomon,et al.  Seismic structure of the Iceland mantle plume , 1997, Nature.

[20]  William H. Press,et al.  Numerical Recipes in FORTRAN - The Art of Scientific Computing, 2nd Edition , 1987 .

[21]  W. Menke,et al.  Reinterpretation of the RRISP-77 Iceland shear-wave profiles , 1996 .

[22]  Arthur L. Lerner-Lam,et al.  How Thick Are the Continents , 1987 .