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The OGS local virtual seismic network in South-Central Europe as an array: exploiting depth phases to locate upper mantle discontinuities
Type
Poster session
Language
English
Obiettivo Specifico
3.3. Geodinamica e struttura dell'interno della Terra
Status
Published
Conference Name
Issued date
July 10, 2011
Conference Location
Vienna (Austria)
Abstract
The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake of magnitude Mw=6.4 occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the North-eastern Italy (NI) Seismic Network: it currently consists of 13 very sensitive broad band and 21 simpler short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data center in Udine. Real time data exchange agreements in place with neighbouring Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of 94 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of North-eastern Italy.
In this study we use P, pP, S and sS phases from global events recorded by the OGS local virtual seismic network in South-Central Europe to study upper mantle discontinuities above earthquakes in the subducted Pacific Plate. We use the time lag between the surface-reflected depth phase and a precursor to determine the discontinuity depth. Accurate estimation of reflector depth depends on a velocity model of the source-side mantle structure. In contrast to typical one-dimensional velocity models, our source-side structure is oceanic, with a shallow Moho and thin crust overlain with water. The time lag between the direct P and pP or S and sS arrivals without accounting for source structure can be as large as 5 s when compared to a purely continental model like iasp91 or ak135.
We identify upper mantle discontinuities using slant stacking and depth-migrated standardized waveforms. The processing shows S-to-P arrivals from the 660 km discontinuity, the 410 km discontinuity, and shallower upper mantle ones of uncertain origin.
In this study we use P, pP, S and sS phases from global events recorded by the OGS local virtual seismic network in South-Central Europe to study upper mantle discontinuities above earthquakes in the subducted Pacific Plate. We use the time lag between the surface-reflected depth phase and a precursor to determine the discontinuity depth. Accurate estimation of reflector depth depends on a velocity model of the source-side mantle structure. In contrast to typical one-dimensional velocity models, our source-side structure is oceanic, with a shallow Moho and thin crust overlain with water. The time lag between the direct P and pP or S and sS arrivals without accounting for source structure can be as large as 5 s when compared to a purely continental model like iasp91 or ak135.
We identify upper mantle discontinuities using slant stacking and depth-migrated standardized waveforms. The processing shows S-to-P arrivals from the 660 km discontinuity, the 410 km discontinuity, and shallower upper mantle ones of uncertain origin.
References
Rawlinson & Kennett (2004) GJI, 157, 332-340.
Schimmel & Paulssen (1997) GJI, 130, 497–505.
Tonegawa & Helffrich (2011) submitted.
Schimmel & Paulssen (1997) GJI, 130, 497–505.
Tonegawa & Helffrich (2011) submitted.
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