G. Patau

Global climate imprint on seismic noise

In the absence of earthquakes, oceanic microseisms are the strongest signals recorded by seismic stations. Using the GEOSCOPE global seismic network, we show that the secondary microseism spectra have global characteristics that depend on the station latitude and on the season. In both hemispheres, noise amplitude is larger during local winter, and close to the equator, noise amplitude is stable over the year. There is an excellent correlation between microseism amplitude variations over the year and changes in the highest wave areas. Considering the polarization of the secondary microseisms, we show that stations in the Northern Hemisphere and close to the equator record significant changes of the secondary microseism source azimuth over the year. During Northern Hemisphere summer, part or all of the sources are systematically located farther toward the south than during winter. Stations in French Guyana (MPG) and in Algeria (TAM) record microseisms generated several thousand kilometers away in the South Pacific Ocean and in the Indian Ocean, respectively. Thus, secondary microseism sources generated by ocean waves which originate in the Southern Hemisphere can be recorded by Northern Hemisphere stations when local sources are weak. We also show, considering a station close to Antarctica, that primary and secondary microseism noise amplitudes are strongly affected by changes of the sea ice floe and that sources of these microseisms are in different areas. Microseism recording can therefore be used to monitor climate changes.

Evidence of earthquake triggering by the solid earth tides

article i nfo Clearevidence forearthquake triggeringbythe earth tides hasremained elusive for morethan a century.Using the largest global earthquake catalog available (the NEIC catalog with 442412 events), we observe a clear correlation (with ∼99% confidence) between the phase of the solid Earth tide and the timing of seismic events: earthquakes occur slightly more often at the time of ground uplift by the Earth tide, i.e. when normal stresses are reduced within the lithosphere. We observe that this phase distribution anomaly is larger for smaller and shallowerearthquakes.Although earthquakes inregionswithdominantlynormalandstrike-slip faulting seem to exhibit more tidal triggering than regions dominated by thrust faulting, there is no statistically significant evidence for a focal mechanism-dependence on earthquake triggering. Finally, we show here that it is highly probablethat the observedtriggeringiscaused bythe solid Earth tide, ratherthan byloading fromthe oceanor atmospheric tides. Although an additional impact due to loading from ocean tides is possible and probable, we cannot detect it here because the earthquake database is not sufficiently complete and homogeneous (more smallmagnitudeearthquakesinoceanicareasareneeded).Ourresultsareconsistentwiththeideaofadamped

Tarapacá intermediate‐depth earthquake (Mw 7.7, 2005, northern Chile): A slab‐pull event with horizontal fault plane constrained from seismologic and geodetic observations

[1] A large (Mw 7.7) intermediate-depth earthquake occurred on 13 June 2005 in the Tarapaca region of the northern Chile seismic gap. Source parameters are inferred from teleseismic broadbands, strong motions, GPS and InSAR data. Relocated hypocenter is found at

Seismicity, deformation and seismic hazard in the western rift of Corinth: New insights from the Corinth Rift Laboratory (CRL)

98 km depth within the subducting slab. The 21-days aftershock distribution, constrained by a postseismic temporary array, indicates a sub-horizontal fault plane lying between the planes of the double seismic zone and an upper bound of the rupture area of 60 km  30 km. Teleseismic inversion shows a slab-pull down dip extension mechanism on a nearly horizontal plane. Total seismic and geodetic moments are

First results of the CRLN seismic network in the western Corinth Rift: evidence for old-fault reactivation

5.5 Â 10 20 N.m, with an averaged slip of 6.5 m from geodesy. The earthquake rupture is peculiar in that the effective velocity is slow, 3.5 Km.s A1 for a high stress-drop, 21 –30 MPa. We propose that rupture was due to the reactivation by hydraulic embrittlement of a inherited major lithospheric fault within the subducting plate. The stress-drop suggests that the region of the slab between planes of the double seismic zone can sustain high stresses. Citation: Peyrat, S., et al. (2006), Tarapaca intermediate-depth earthquake (Mw 7.7, 2005, northern Chile): A slab-pull event with horizontal fault plane constrained from seismologic and geodetic observations, Geophys.