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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS005 1905 - 1923 Symposium Non-instrumental seismometry - Global and regional parameters of paleoseismology; implications for fault scaling and future earthquake hazard Convener : Dr. David Schwartz, Mrs. Suzanne Hecker, Dr. Gianluca Valensise, Dr. Kelvin Berryman Co-Convener : Dr. Paolo Marco De Martini, Dr. Eullia Masana, Dr. Daniela Pantosti For the General scopes see introduction to symposium JSS004. This session deals mainly with the integration of earthquake and fault rupture parameters across the seismological/geological/geophysical boundaries exploring the difference in scaling between large and small earthquakes. Another interesting aspect we would like to discuss concerns the evidence for linear or nonlinear relationship between average displacement and fault length for large dip-slip and strike-slip earthquakes. These have been the topic of considerable debate in the last years and we hope that the contributions to the session will advance our knowledge at both global and regional scales. The session includes, but is not restricted to, the following topics: - relationships between paleoseismological parameters (surface rupture length and average surface displacement) and earthquake magnitude estimates; - comparison of paleoseismological parameters obtained from the pre-instrumental epoch as against modern earthquakes studies; - comparison of source parameters obtained by different methodologies (geodesy, geology, seismology and geophysics). We particularly welcome contributions based on results from fieldwork, high-resolution geophysical measurements, remote sensing studies and analogue models. We also encourage presentations dealing with problems of under- or over-estimation of earthquake magnitude resulting from spatial variability of slip and scarp degradation processes at the surface.

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS005 Oral Presentation 1905 Empirical relations among magnitude and rupture characteristics, through mechanical modeling of interacting faults and fault patches Mr. Olaf Zielke SESE ASU Ramon J Arrowsmith Determining the magnitude of paleo-earthquakes is as difficult as it is important. These data are crucial components to assess seismic hazard: knowing the slip and date of the last major earthquake that occurred on a specific fault, the derived long-term slip-rate can be used to estimate the timing of the next large event assuming that they are time predictable. Furthermore, long-term slip-rates define the slip-distribution within a fault system constraining the regional stress field a crucial component to run increasingly realistic fault models. Such models may characterize the seismic hazard at fault system level by incorporating processes such as fault interaction In order to determine paleo-magnitudes, earthquake-related geomorphic features such as rupture length, average surface displacement, or maximum surface displacement are utilized, assuming that an earthquake of a specific size will cause surface features of correlated size. The well known Wells & Coppersmith (1994) paper defined empirical relationships between these and other parameters, based on events with known magnitudes and rupture characteristics. However, because their study depended on a limited number of observed events, the uncertainties on their correlations are rather large, coefficients ranging from 0.71 to 0.95. In addition, they were only able to differentiate between the three general fault types (strike, normal, reverse). Therefore, the effect of oblique slip on rupture characteristics was not addressed affecting the derived relationships. We have developed a boundary element model, based on derivations by Okada (1992) that simulates faulting and fault interaction of any number of arbitrarily oriented, located, and loaded faults. For the study presented here, we simulate faulting along a single fault divided into a large number of (~5000) elements and utilize a simple Coulomb static/dynamic friction law to create synthetic seismic catalogs: Each time step the faults are tectonically loaded. When the stress on an element exceeds its static frictional strength, it starts to slip, corresponding to the stress drop to its dynamical frictional strength. Due to a fault interaction algorithm, this may cause other elements to fail as well, cascading into events of all sizes, populating the synthetic seismic catalog. This catalog will be used to develop a new set of more complete magnitude vs. rupture characteristics plots in the sense of Wells & Coppersmith (1994). Several enhancements justify this approach: A) We can use seismic catalog of any length. B) Our catalog will be not limited to large, rare, surface rupturing earthquakes but contain the full spectrum of possible magnitudes. C) The uncertainty in the correlations will be small, providing a more realistic assessment of variability. D) How different parameters such as oblique slip, fault sinuosity, or fault roughness affect the magnitude vs. rupture characteristics relationships can be explored. In addition to a full exploration of relevant parameters from Wells & Coppersmith, we will also study system level properties such as fault sinuosity, fragmentation, slip obliquity, etc. Since these are parameters that can be constrained in the field, our experiment will help paleo-seismologist to interpret their findings in a more complete way that treats faults not as individual, isolated entities but as part of a system of interacting structures. Keywords: mechanical modeling, interaction, synthetic seismicity

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