HR: 11:35h
AN: S52A-06    [Abstracts]
TI: Variation of Earthquake Scaling (Dmax-L) with Long-Term Fault Evolution
AU: * MANIGHETTI, I
EM: imanighe@obs.ujf-grenoble.fr
AF: LGIT, BP 53, Grenoble, 38041 France
AU: Cotton, F
EM: fabrice.cotton@obs.ujf-grenoble.fr
AF: LGIT, BP 53, Grenoble, 38041 France
AU: Campillo, M
EM: campillo@obs.ujf-grenoble.fr
AF: LGIT, BP 53, Grenoble, 38041 France
AB: A critical issue in earthquake mechanics is to be capable of determining the maximum displacement and magnitude than can be produced on a fault of known dimensions. Available measurements of length (L) and maximum displacement (Dmax) on faults broken during past earthquakes are dense enough for the Dmax-L scaling relationship to be re-examined (after Wells and Coppersmith, 1994). We do that here on the basis of the Dmax-L data compiled by Manighetti et al. (2005). Because most co-seismic slip distributions are triangular in shape on average (see previous reference), Dmax = 2*Dmean, so that any conclusion drawn from Dmax-L scaling applies to Dmean-L scaling. Following Miller (2002), we hypothesize that the relationship between Dmax and L depends on fault strength. We further assume that the strength of a fault depends on its long-term evolution, i.e., a fault being slipping for long ('mature') is weaker than a recently formed fault ('immature'). With these hypotheses in mind, we identify the faults having broken in the considered past earthquakes, document their long-term evolution, and examine how the Dmax-L scaling varies both along these faults and from one fault to the other. Taken together, the Dmax-L data define four major trends, with very few data in between. Along each trend, Dmax/L is roughly constant (at most equal per trend to 2, 4, 6-8, and 10-20.10-5) although slightly decreasing with length along the steepest trends. Earthquakes falling on the two lowest trends pertain to mature, lithospheric scale-faults, being rather plate boundaries on the lowest trend (North Anatolian and San Andreas, subduction zones), and intra-plate faults on the trend due 'above' (Kunlun, Xian Shui He [but SE tip], Bolnai, W tip of North Anatolian, Main Zagros Recent thrust). By contrast, earthquakes falling on the two steepest trends pertain to younger, smaller and less mature faults (Tien Shan, normal Tibet faults). Most of these faults are found at the tip (SE tip of Xian Shui He, N and S tips of Lut block bounding faults), associated to (faults associated to San Andreas), or in between major structures (Haiyuan zone, Karakax-Karakorum junction, Tabriz fault). The largest Dmax/L ratios are found for earthquakes having occurred in zones of strongly oblique cross-cutting faults (Jiali-normal Tibet faults, Haiyan-Ordos, Bolnai-Altai), and in some regions of normal faulting (Greece, Basin and Range). These preliminary results suggest that knowing the long-term evolution of faults may help anticipating better the maximum displacements that these faults may produce in future earthquakes, and identifying the faults or fault sections with larger stress drops (larger Dmax/L ratios). For instance, while the NAF is among those producing the smallest Dmax/L ratios hence the smallest stress drops, its western propagating tip (Marmara Sea area) is made of segments with higher stress drops. Similarly, the secondary faults distributed around San Andreas are capable of producing higher stress drops than that fault. The Tien Shan, SE tip of Xian Shui He, and Haiyuan are among the faults having the highest stress drops in Asia. Our revised scaling laws suggest that a future earthquake that would break the 220 km-long Tianzhu seismic gap along the Haiyuan fault (Gaudemer et al., 1995) would produce a Dmax of 14-18 m; more than the displacement predicted by the available scaling regressions (10.5 m according to Wells and Coppersmith, 1994). Similarly, an earthquake that would break the 200 km-long Xidatan seismic gap on the Kunlun fault (Van der Woerd et al., 1998) would produce a Dmax of 7-8 m, less than the value predicted by the commonly used scaling laws (9.5 m).
DE: 1209 Tectonic deformation (6924)
DE: 7200 SEISMOLOGY
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
SC: Seismology [S]
MN: Fall Meeting 2005