HR: 0800h
AN: S41C-1038 [Abstracts]
TI: Using the initial phase of the gravest Earth's free
oscillations to study the source of large earthquakes
AU: * Rivera, L
EM: luis@sismo.u-strasbg.fr
AF: IPGS-EOST, Université Louis Pasteur;
5, rue René Descartes, Strasbourg, 67084
France
AU: Lambotte, S
EM: sophie.lambotte@eost.u-strasbg.fr
AF: IPGS-EOST, Université Louis Pasteur;
5, rue René Descartes, Strasbourg, 67084
France
AU: Hinderer, J
EM: jacques.hinderer@eost.u-strasbg.fr
AF: IPGS-EOST, Université Louis Pasteur;
5, rue René Descartes, Strasbourg, 67084
France
AB:
Both gravimeters and broad band seismometers can
record for weeks the Earth's free oscillations excited
by large earthquakes. When long enough high-quality records
are available, it is possible to properly separate the
individual singlets of the gravest modes in the spectra.
Each one of those singlets is characterized by a frequency,
ω, a quality factor, Q, an amplitude and a phase.
Whereas the two former exclusively depend on the Earth's
structure, the last two are strongly dependent on the mechanism,
duration and geometry of the fault. We focus here on the use of
phase information to constrain the geometry of the source. The
contribution of the faintness of the fault to the initial phase
is an additive term which is linear both in the duration and
length of the fault. This term can be recovered by subtracting
the predicted phase for a point source from the observed initial
phase. This procedure leads to extremely robust estimation of the
overall source model from single station records. We test this
technique with several recent large earthquakes as the 2001 Peruvian
earthquake or the 2004 Sumatra giant event. We use mainly Geoscope
and Iris-Ida seismological data and GGP gravimetric data. When
available, we use atmospheric pressure data to reduce the barometric
effect on the free oscillations data. This correction proved is often
crucial to achieve reliable initial phase estimates.
DE: 3255 Spectral analysis (3205, 3280)
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory
SC: Seismology [S]
MN: Fall Meeting 2005