Inversion for parameters of tensile earthquakes

The tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane. The proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic (ISO), compensated linear vector dipole (CLVD), and double-couple (DC) components in seismic moment tensors. The most significant parameters inverted are the λ/μ ratio at the fault (denoted as the κ parameter) and the inclination α of the slip vector from the fault. The κ parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes. The inclination α can be accurately determined from the DC component in the moment tensor because the DC component rapidly decreases with increasing α. For example, the inclination of 20° causes DC being ∼50–60% only. The inversion is applied to earthquakes which occurred in January 1997 in West Bohemia, Czech Republic. It is shown that some of these earthquakes display tensile faulting. The κ parameter is ∼0.1. The inclination of the slip from the fault attains values of up to 20°. This inclination is a result of tensile traction and reduced shear traction along the fault and high-fluid pressure in the region.

[1]  G. Foulger.  HENGILL TRIPLE JUNCTION, SW ICELAND 2. ANOMALOUS EARTHQUAKE FOCAL MECHANISMS AND IMPLICATIONS FOR PROCESS WITHIN THE GEOTHERMAL RESERVOIR AND AT ACCRETIONARY PLATE BOUNDARIES , 1988 .

[2]  V. Vavryčuk,et al.  Approximate retrieval of the point source in anisotropic media: numerical modelling by indirect parametrization of the source , 2000 .

[3]  G. Backus.  Long-Wave Elastic Anisotropy Produced by Horizontal Layering , 1962 .

[4]  L. Rivera,et al.  ON THE RESOLUTION OF THE ISOTROPIC COMPONENT IN MOMENT TENSOR INVERSION , 1997 .

[5]  Paul G. Richards,et al.  Quantitative Seismology: Theory and Methods , 1980 .

[6]  Tomáš Fischer,et al.  Scenario of the January 1997 West Bohemia Earthquake Swarm , 2000 .

[7]  S. Sipkin.  Interpretation of non‐double‐couple earthquake mechanisms derived from moment tensor inversion , 1986 .

[8]  James N. Brune,et al.  Frictional heat generation and seismic radiation in a foam rubber model of earthquakes , 1994 .

[9]  Larry G. Mastin,et al.  Regional patterns of tectonic stress in Europe , 1992 .

[10]  M. J. Randall,et al.  The compensated linear‐vector dipole: A possible mechanism for deep earthquakes , 1970 .

[11]  A. D. Miller,et al.  Non‐double‐couple earthquakes 2. Observations , 1998 .

[12]  J. Šílený.  Earthquake source parameters and their confidence regions by a genetic algorithm with a ‘memory’ , 1998 .

[13]  Robert B. Herrmann,et al.  A Student’s Guide to and Review of Moment Tensors , 1989 .

[14]  William R. Walter,et al.  Spectra of seismic radiation from a tensile crack , 1993 .

[15]  G. Foulger.  HENGILL TRIPLE JUNCTION, SW ICELAND 1. TECTONIC STRUCTURE AND THE SPATIAL AND TEMPORAL DISTRIBUTION OF LOCAL EARTHQUAKES , 1988 .

[16]  T. Dahm,et al.  Relative moment tensor inversion based on ray theory: theory and synthetic tests , 1996 .

[17]  V. Vavryčuk.  Crustal anisotropy from local observations of shear-wave splitting in West Bohemia, Czech Republic , 1993, Bulletin of the Seismological Society of America.

[18]  C. Frohlich.  Earthquakes with Non—Double-Couple Mechanisms , 1994, Science.

[19]  C. Scholz.  The Mechanics of Earthquakes and Faulting , 1990 .

[20]  Mechanisms of local earthquakes in 3-D inhomogeneous media determined by waveform inversion , 1995 .

[21]  John W. Gephart,et al.  Stress and the direction of slip on fault planes , 1990 .

[22]  A. D. Miller,et al.  Non‐double‐couple earthquakes 1. Theory , 1998 .

[23]  T. Dahm,et al.  Comparison of Absolute and Relative Moment Tensor Solutions For The January 1997 West Bohemia Earthquake Swarm , 2000 .

[24]  Kampf,et al.  Gas flux distribution in mineral springs and tectonic structure in the western Eger Rift , 1998 .

[25]  Tomáš Fischer,et al.  The Western Bohemia/Vogtland Region in the Light of the Webnet Network , 2000 .

[26]  H. Shimizu,et al.  A tensile — shear crack model for the mechanism of volcanic earthquakes , 1987 .

[27]  John W. Gephart,et al.  An improved method for determining the regional stress tensor using earthquake focal mechanism data: Application to the San Fernando Earthquake Sequence , 1984 .

[28]  Andrew J. Michael,et al.  Use of focal mechanisms to determine stress: A control study , 1987 .

[29]  Tomáš Fischer,et al.  Refined Locations of The Swarm Earthquakes In The Nový Kostel Focal Zone and Spatial Distribution of The January 1997 Swarm In Western Bohemia, Czech Republic , 2000 .

[30]  Peggy A. Johnson,et al.  Rupture mechanism and interface separation in foam rubber models of earthquakes: a possible solution to the heat flow paradox and the paradox of large overthrusts , 1993 .

[31]  A. D. Miller,et al.  Non‐double‐couple earthquake mechanisms at the Hengill‐Grensdalur Volcanic Complex, Southwest Iceland , 1997 .

[32]  T. Lay,et al.  Data‐dependent non‐double‐couple components of shallow earthquake source mechanisms: Effects of waveform inversion instability , 1994 .

[33]  C. Scholz,et al.  Dilatancy in the fracture of crystalline rocks , 1966 .

[34]  D. Gajewski,et al.  Vertical seismic profile synthetics by dynamic ray tracing in laterally varying layered anisotropic structures , 1990 .

[35]  Ragnar Slunga,et al.  Stress tensor inversion using detailed microearthquake information and stability constraints: Application to Ölfus in southwest Iceland , 1999 .

[36]  Bruce R. Julian,et al.  Non‐double‐couple earthquake mechanisms at the Geysers Geothermal Area, California , 1996 .

[37]  Jiří Vaněk,et al.  Magma Intrusions and Earthquake Swarm Occurrence in the Western Part of the Bohemian Massif , 1999 .