HR: 1330h
AN: S42D-0200    [PDF]
TI: What can Rotational Measurements Teach us About Earthquake Rupture Histories?
AU: * Cochard, A
EM: alain@geophysik.uni-muenchen.de
AF: Dpt Earth Env Sci, Geophys Sec, Theresienstrasse 41, Muenchen, 80333 Germany
AU: Igel, H
EM: igel@geophysik.uni-muenchen.de
AF: Dpt Earth Env Sci, Geophys Sec, Theresienstrasse 41, Muenchen, 80333 Germany
AB: The general motion of a deformable body is uniquely specified by 3 components of displacement (those measured by classical seismometers), 6 components of strain, and 3 components of rotation. While it is standard to observe translational motions, and quite usual to measure strain, rotations had little attention, partly because rotational effects generated by earthquakes were thought to be small (e.g., Bouchon and Aki, 1982), and partly because no instruments existed which directly measured absolute rotations. Recently, there has been a revival of interest for rotations due to a growing body of observational evidence that, at least in some cases, rotational motions are indeed strong (Takeo and Ito, 1997, Takeo, 1998), while, at the same time, very precise instruments are becoming available. Here, we numerically study the effects of various kinematic scenarios on rotations. In some cases, the effects on rotations appear much more marked than those on translations, i.e., rupture histories with very similar translational seismograms show pronounced differences in the collocated rotational motions. This is the case, e.g., for a circular crack rupture with constant slip velocity on the one hand, and a more realistic inverse square root singularity Kostrov-like slip-velocity profile on the other hand. We also report effect on rotations of fault segmentation and variation of rupture velocity. We anticipate that taking into account rotational measurements will help constraining inversions of kinematic rupture histories.
DE: 7209 Earthquake dynamics and mechanics
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting