FAAS and Antelope: two automatic earthquake location systems in the Northeastern Italy and surrounding areas

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Tuning Antelope configuration for best earthquake location

The large amount of digital data recorded by permanent and temporary seismic networks makes automatic analysis of seismograms and automatic wave onset time picking schemes of great importance for timely and accurate earthquake locations. Since 2002 the Centro di Ricerche Sismologiche (CRS, Seismological Research Center, http://www.crs.inogs.it/) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) is involved in the EU Interreg IIIA project Trans-national seismological networks in the South-Eastern Alps together with other four institutions: the Earth Science Department of the Trieste University in Italy, the Civil Protection Department of the Friuli-Venezia Giulia Autonomous Region (DPCFVG) in Italy, the Environmental Agency of the Republic of Slovenia (ARSO), and the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). The Antelope software suite has been chosen as the common basis for real-time data exchange, rapid location of earthquakes and alerting. Each institution has an instance of Antelope running at its data center and acquires data in real-time from its seismic stations and those of the other partners. Antelope detects events by STA/LTA algorithm and the association is based on location by grid search. The actual set up for fast location capabilities uses only P arrivals. The location is performed by grid search over 87x81 nodes for an extension of 7x6.4 degrees (corresponding to cells of 8.9 km in longitude and 8.7 km in latitude) centered in Lat=46.26o, Lon=13.28o with depth steps at 0, 2, 4, 6, 8, 10, 12, 14, 16, 20 and 24 km, using the 1D uniform velocity model IASPEI91. Recently the CRS acquired a new SUN cluster hardware: consequently a new set up of the Antelope software suite has been tested to improve location accuracy using a denser grid and also S-phases arrivals. The results of the performances of the new configuration will be shown; in particular, we compute the variance of the differences between the location data sets of the two different configurations, inferring the precision of each data set by comparing them with the reference OGS bulletin database. We adopt the recall, precision and accuracy estimators to appraise objectively the results and compare them with those of the other datasets.PublishedPerugia (Italy)1.1. TTC - Monitoraggio sismico del territorio nazionaleope

Seismotectonic and macroseismic characteristics of the earthquake of Bovec (NW Slovenia: April 12, 1998)

On the 12th Apri1 1998, a wide area in the middle valley of the Soča/Isonzo River near Bovec (NW Slovenia) was affected by an earthquake of MD = 5.6. It was followed by a long seismic sequence from which the 40 aftershocks, with MD ≥3.0 recorded until the 30th June 1998, have been analysed. The study area belongs to the External Dinarides.: it is characterised by a set of dextral NW-SE strike-slip faults that act as kinematic release for the Eastern Southalpine Chain. The main shock presents a classical focal mechanism of strike-slip fault (P = 179/02; T= 269/02) with vertical planes of motion, NW-SE (dextral) and NE-SW (sinistral), and a hypocentre depth of about 15 km. The main aftershock of the 6th May 1998 (MD = 4.6) shows the same focal mechanism, with the hypocentre at about 15 km and the epicentre shifted 6 km towards SE. Also the aftershocks with 3.5 ≤ MD ≤ 4.0 show a prevailing strike-slip focal mechanism. On the contrary, the focal mechanism of the events with 3.0 ≤ MD < 3.5 are more diversified: the earthquakes with transtensional or extensional focal mechanism with planes ranging from NW-SE to N-S prevail over the earthquakes which present a fault plane solution typical of low-angle NW-SE to NE-SW trending reverse faults. Both the main shock and the aftershocks are kinematically compatible with the actual strike-slip tectonic framework of this region. The Čez Potoče fault, one of the main dextral NW-SE strike-slip faults, along which the main shock and aftershock hypocentres are distributed, is considered to be the seismogenetic fault. The temporal analysis suggests a migration of the events towards SE along this fault. The analysis of the distribution and the type of damages indicated that there is no correspondence between the instrumental epicentre and the macroseismic one. The intensity of the latter has been valued equal to the VIII-IX MCS, with heavy structural settlings and noteworthy phenomena of site amplification. The earthquake caused some effects also in the Friuli-Venezia Giulia region (macroseismic intensity surveyed equal to V-VI MCS) where the anomalous distribution of the damage appears to be connected with the partial or full retrofitting of the buildings after the earthquake of 1976. Such a fact once more shows the fundamental importance of strengthening the buildings, particularly the old ones, in order to mitigate the seismic risk

FAAS and Antelope: two automatic earthquake location systems in the Northeastern Italy and surrounding areas

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Performances of two automatic earthquake location systems in the north-eastern italy

PublishedGENEVAope