IMPROVEMENT IN DETECTION, LOCATION, AND IDENTIFICATION OF SMALL EVENTS THROUGH JOINT DATA ANALYSIS BY SEISMIC STATIONS IN THE MIDDLE EAST/EASTERN MEDITERRANEAN REGION

The joint project of Israel, Cyprus, and Turkey is devoted to the collection of the Ground Truth (GT) data for calibration of the regional International Monitor ting System (IMS) stations, characterization of the national regional networks, and development of the data-processing software. During the second year of the project activity, we have extended the GT database and checked (by a relocation experiment) 70 collected calibration GT events in the East Mediterranean region. These included 19 explosions within the footprint of the ISN (13 GT0 explosions and six GT2 quarry blasts), and 51 GT5 earthquakes from Israel, Cyprus, and three seismic provinces Izmit, Duzce and Adana in Turkey. For each of the calibration events, a computational relocation experiment was performed to make a quality tuning of the obtained source parameter estimates: coordinates (X, Y, Z) and origin time T0, and ensure that these estimates are reliable and accurate enough. For this experiment we have elaborated special software “RELOC,” including the “SEIS” hypocenter search program, and new codes for estimation of the 90% hypocenter error ellipsoid. For EIL, MRNI and BRAR IMS stations, station-specific source corrections (SSSC) have been computed using GT coordinates and origin times, obtained through the relocation experiment. Most deviations of the observed P, S travel times from the IASPEI91 velocity model for Israel GT events were compensated by application of the local 1-D model. However, the similar attempt on regional scale to explain deviations from the 1-D model by the 3-D model CUB of the Colorado University did not provide the expected improvement. Errors observed in SSSCs, constructed directly from empirical travel times, can be reduced by using more accurate velocity model. For updating the 1-D velocity models in the GT events, the VELEST joint epicenter solution program was applied in the area of Adana Basin (Cilician network, TUBITAK) and ISN region (GII). The data set contained 244 reliable Adana events and 170 ISN events of ML > 2.5 with good P and S readings. Initial RMS was 0.5 and 0.67 sec for each of the networks respectively and after a number of iterations, new 1-D velocity models have been achieved with RMS value of 0.3 sec for both of the networks. In order to extend the Middle East GT0 database, GII conducts a series of large (20-25 tons) inland blasts, using the facilities of Israeli quarries. These explosions will provide data complementary to the Dead Sea underwater calibration shots of November 1999. A 25-ton single-fired calibration explosion of special experimental design was conducted at Rotem phosphate quarry in Negev, Southern Israel, on May 21, 2002. It was preceded by smaller trial shots, for estimating safety conditions and seismic efficiency of the large shot. Obtained results confirmed the estimations. The expected magnitude 3.0 was achieved. Records were obtained at numerous permanent and portable short-period (SP) and broadband (BB) seismometers as well as accelerographs, in the distance range 0.3 – 450 km, in Israel, Jordan and Cyprus. Compared to other calibration shots, the Rotem 25-ton blast showed seismic strength similar to the same size Balapan (STS, Kazakhstan) explosion, and 0.5-ton Dead Sea shot. For all controlled quarry blasts, a detailed GTI was collected. The recorded explosions and earthquakes provided data for corrections of regional travel times for regional networks and IMS stations EIL and the new array AS049 at Mt. Meron, verification and improvement of velocity models, attenuation (amplitude-distance) and magnitude-yield relations, characterization of new seismic sources and local mining practices, and multi-station discrimination analysis. 271 24th Seismic Research Review – Nuclear Explosion Monitoring: Innovation and Integration