Journal of Conference Abstracts

Stages of an Earthquake Cycle and Evolving Patterns of Seismicity and Faults in a Rheologically Layered Lithosphere

Vladimir Lyakhovsky (vladi@cc.huji.ac.il)¹, Yehuda Ben-Zion (benzion@terra.usc.edu)² & Amotz Agnon (amotz@cc.huji.ac.il)¹

¹Inst. Earth Sci., Hebrew University, Givat Ram, Jerusalem, 91904, Israel

²Dept. Earth Sci., Univ. Southerm California, Los Angeles, 90089-0740, CA, U.S.A.

We study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust (nominally 15 km thick) governed by damage rheology, over a viscoelastic substrate. The damage rheology has two types of functional coefficients: (1) a "generalized internal friction" separating states associated with material degradation and healing, and (2) damage rate coefficients for positive (degradation) and negative (healing) changes (Lyakhovsky et al., 1997). The evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation. This simulates the creation and healing of fault systems in the upper seismogenic zone. The seismogeneic upper crust is viscoelastically coupled to the substrate, so steady plate motion drives the deformation. The calculations employ vertically-averaged variables of the thin sheet approximation for viscous component of the motion and 3-D Green function for elasatic coupling with the sublithospheric mantle.

To focus on basic features of a large strike-slip fault system, we start with simplified geometry of the seismogenic crust by prescribing there initial conditions consisting of a narrow damage zone in an otherwise damage-free plate. For this configuration, the model generates an earthquake cycle with distinct inter-, pre-, co-, and post-seismic periods. Model evolution during each period is controlled by a subset of parameters, which we constrain using geophysical, geodetical, and seismological data. In the more generic case with random initial damage distribution, the model generates large crustal faults and subsidiary branches with complex geometries. Preliminary results indicate that high healing rate, describing systems with relatively short memory, leads to the development of geometrically regular fault systems, and the characteristic frequency-size earthquake distribution. Conversely, low healing rate (relatively long memory) leads to the development of a network of disordered fault systems, and the Gutenberg-Richter earthquake statistics. The statistics depend on the space-time window of the observational domain, i.e., the response is non ergodic. For some parameters, the results exhibit alternating overall switching of response, from periods of intense seismic activity to periods during which the deformation occurs aseismically.

Lyakhovsky et al., JGR, (1997)