Time filter

Source Type

Landa E.,Avenue Of Luniversite | Keydar S.,Geophysical Institute of Israel | Jan Moser T.,Van Alkemadelaan 550A
Geophysical Prospecting | Year: 2010

We review the multifocusing method for traveltime moveout approximation of multicoverage seismic data. Multifocusing constructs the moveout based on two notional spherical waves at each source and receiver point, respectively. These two waves are mutually related by a focusing quantity. We clarify the role of this focusing quantity and emphasize that it is a function of the source and receiver location, rather than a fixed parameter for a given multicoverage gather. The focusing function can be designed to make the traveltime moveout exact in certain generic cases that have practical importance in seismic processing and interpretation. The case of a plane dipping reflector (planar multifocusing) has been the subject of all publications so far. We show that the focusing function can be generalized to other surfaces, most importantly to the spherical reflector (spherical multifocusing). At the same time, the generalization implies a simplification of the multifocusing method. The exact traveltime moveout on spherical surfaces is a very versatile and robust formula, which is valid for a wide range of offsets and locations of source and receiver, even on rugged topography. In two-dimensional surveys, it depends on the same three parameters that are commonly used in planar multifocusing and the common-reflection surface (CRS) stack method: the radii of curvature of the normal and normal-incidence-point waves and the emergence angle. In three dimensions the exact traveltime moveout on spherical surfaces depends on only one additional parameter, the inclination of the plane containing the source, receiver and reflection point. Comparison of the planar and spherical multifocusing with the CRS moveout expression for a range of reflectors with increasing curvature shows that the planar multifocusing can be remarkably accurate but the CRS becomes increasingly inaccurate. This can be attributed to the fact that the CRS formula is based on a Taylor expansion, whereas the multifocusing formulae are double-square root formulae. As a result, planar and spherical multifocusing are better suited to model the moveout of diffracted waves. © 2010 European Association of Geoscientists & Engineers.

Ezersky M.,Geophysical Institute of Israel | Frumkin A.,Hebrew University of Jerusalem
Geomorphology | Year: 2013

There are two conflicting models of sinkhole development along the Dead Sea (DS). The first one considers structural control on sinkholes, constraining them to tectonic lineaments. This hypothesis is based on seismic reflection studies suggesting that sinkholes are the surface manifestations of active neotectonic faults that may serve as conduits for under-saturated groundwater, enabling its access across aquiclude layers. Another hypothesis, based on results of multidisciplinary geophysical studies, considers the salt edge dissolution front as the major site of sinkhole formation. This hypothesis associates sinkholes with karstification of the salt edge by deep and shallow undersaturated groundwater. Our recent seismic reflection and surface wave studies suggest that salt formed along the active neotectonic faults. Sinkholes form in a narrow strip (60-100. m wide) along a paleo-shoreline constrained by faults and alluvial fans which determined the edge of the salt layer. This scenario reconciles the two major competing frameworks for sinkhole formation. © 2013 Elsevier B.V.

Hofstetter A.,Geophysical Institute of Israel
Journal of Seismology | Year: 2014

First motion fault plane solutions provide invaluable important information on the mechanism of seismogenic faults and the orientation of the local stress field. However, there are severe limitations and shortcomings regarding the reliability of the calculated solution and how accurately it reflects the real earthquake mechanism. In this study, we examine the dependence of the three mechanisms of ideal strike slip, normal, and thrust on different quality estimators, i.e., event location, velocity model, and reverse polarity stations. We intentionally perturb the original fault plane solutions by changing only one of the parameters that control the solution at a time and compare the perturbed solutions with the real one. Finally, we randomly perturb all the parameters for each earthquake in a large set of events. We then discuss the effect of the perturbations on the reliability of the solution. © 2013 Springer Science+Business Media Dordrecht.

Meirova T.,Tel Aviv University | Pinsky V.,Geophysical Institute of Israel
Geophysical Journal International | Year: 2014

For the first time, a regional seismic attenuation for the Israel region is quantitatively estimated as a combination of intrinsic and scattering attenuations. We use a multiple lapse time windows analysis (MLTWA) to determinate the relative contributions of intrinsic absorption and scattering processes to the total regional attenuation in the crust. A single isotropic scattering model assuming a uniform half-space lithosphere is used to fit MLTWA predicted and measured energies from the records of 232 regional earthquakesrecorded at 17 short-period and 5 broad-band local seismic stations. Analysis is performed for a set of 10 frequencies between 0.5 and 10 Hz. The frequency-dependent quality factor Q obtained by MLTWA ranges between Q = 77 f0.96 in the Northern Israel and Q = 132 f0.96 in Southern Israel. Independent estimates of regional coda Q value based on S-wave coda decay rate obtained by averaging of five broad-band Israel Seismic Network stations are approximated by the relation Qc = 126 f 1.05. As a whole, our findings indicate that in the Israel region, intrinsic absorption prevails over scattering attenuation. Separateanalysis for three tectonically different regions in Israel region-Galilee-Lebanon, Judea-Samaria and Eastern Sinai-shows a regional dependence of attenuation parameters. The variation of attenuation characteristics implies different physical mechanisms of seismic attenuation in the Israel region and is related to the differences of structure in the Earth's crust beneath Israel. Such variation in the attenuation patterns is in agreement with the assumption that Northern Israel is tectonically more active than Southern Israel and that in the northern and central parts of Israel the upper crust is more heterogeneous than in the southern part. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Pinsky V.,Geophysical Institute of Israel
Journal of Seismology | Year: 2014

In June 2012, the Israeli government approved the offer of the creation of an earthquake early warning system (EEWS) that would provide timely alarms for schools and colleges in Israel. A network configuration was chosen, consisting of a staggered line of ∼100 stations along the main regional faults: the Dead Sea fault and the Carmel fault, and an additional ∼40 stations spread more or less evenly over the country. A hybrid approach to the EEWS alarm was suggested, where a P-wave-based system will be combined with the S-threshold method. The former utilizes first arrivals to several stations closest to the event for prompt location and determination of the earthquake’s magnitude from the first 3 s of the waveform data. The latter issues alarms, when the acceleration of the surface movement exceeds a threshold for at least two neighboring stations. The threshold will be chosen to be a peak acceleration level corresponding to a magnitude 5 earthquake at a short distance range (5–10 km). The warning times or lead times, i.e., times between the alarm signal arrival and arrival of the damaging S-waves, are considered for the P, S, and hybrid EEWS methods. For each of the approaches, the P- and the S-wave travel times and the alarm times were calculated using a standard 1D velocity model and some assumptions regarding the EEWS data latencies. Then, a definition of alarm effectiveness was introduced as a measure of the trade-off between the warning time and the shaking intensity. A number of strong earthquake scenarios, together with anticipated shaking intensities at important targets, namely cities with high populations, are considered. The scenarios demonstrated in probabilistic terms how the alarm effectiveness varies depending on the target distance from the epicenter and event magnitude. © 2014, Springer Science+Business Media Dordrecht.

Gitterman Y.,Geophysical Institute of Israel | Hofstetter R.,Geophysical Institute of Israel
Pure and Applied Geophysics | Year: 2014

Three large-scale on-surface explosions were conducted by the Geophysical Institute of Israel (GII) at the Sayarim Military Range, Negev desert, Israel: about 82 tons of strong high explosives in August 2009, and two explosions of about 10 and 100 tons of ANFO explosives in January 2011. It was a collaborative effort between Israel, CTBTO, USA and several European countries, with the main goal to provide fully controlled ground truth (GT0) infrasound sources, monitored by extensive observations, for calibration of International Monitoring System (IMS) infrasound stations in Europe, Middle East and Asia. In all shots, the explosives were assembled like a pyramid/hemisphere on dry desert alluvium, with a complicated explosion design, different from the ideal homogenous hemisphere used in similar experiments in the past. Strong boosters and an upward charge detonation scheme were applied to provide more energy radiated to the atmosphere. Under these conditions the evaluation of the actual explosion yield, an important source parameter, is crucial for the GT0 calibration experiment. Audio-visual, air-shock and acoustic records were utilized for interpretation of observed unique blast effects, and for determination of blast wave parameters suited for yield estimation and the associated relationships. High-pressure gauges were deployed at 100-600 m to record air-blast properties, evaluate the efficiency of the charge design and energy generation, and provide a reliable estimation of the charge yield. The yield estimators, based on empirical scaled relations for well-known basic air-blast parameters-the peak pressure, impulse and positive phase duration, as well as on the crater dimensions and seismic magnitudes, were analyzed. A novel empirical scaled relationship for the little-known secondary shock delay was developed, consistent for broad ranges of ANFO charges and distances, which facilitates using this stable and reliable air-blast parameter as a new potential yield estimator. The delay data of the 2009 shot with IMI explosives, characterized by much higher detonation velocity, are clearly separated from ANFO data, thus indicating a dependence on explosive type. This unique dual Sayarim explosion experiment (August 2009/January 2011), with the strongest GT0 sources since the establishment of the IMS network, clearly demonstrated the most favorable westward/eastward infrasound propagation up to 3,400/6,250 km according to appropriate summer/winter weather pattern and stratospheric wind directions, respectively, and thus verified empirically common models of infrasound propagation in the atmosphere. © 2012 Springer Basel AG.

Bonner J.,Weston Geophysical Corp. | Waxler R.,University of Mississippi | Gitterman Y.,Geophysical Institute of Israel | Hofstetter R.,Geophysical Institute of Israel
Bulletin of the Seismological Society of America | Year: 2013

The January 2011 calibration explosions at the Sayarim Military Range in the Negev Desert, Israel, provide a unique dataset to study seismic and acoustic partitioning for surface sources at near-source and local distances.We present an analysis of the seismic and overpressure/acoustic signals generated from two explosions, which included 10,240 and 102,080 kg of mainly ANFO with some Composition B, detonated on the surface, on 24 and 26 January, respectively, at different times of the day. A temporary seismo-acoustic-overpressure network was deployed at distances between 0.1 and 39 km to supplement data from permanent stations in Israel. The near-source data confirm the explosions produced overpressure signals consistent with complete and simultaneous surface detonation of 7.4 and 76.8 metric tons of TNT-equivalent explosives. We observe acoustic amplification at local distances (>5 km) south of the larger explosion that can be explained by a low-altitude southward flowing wind at the detonation time. For the smaller shot, the southward flow was not present and amplification was not observed in the pressure data. We present results of modeling these overpressure data with blast pressure scaling models with and without meteorological data. Seismic phases generated by the surface shots include P waves, fundamental and higher mode Rayleigh waves, and Love waves that appear to have been generated at or very near the explosion source. The seismic ground motion is less than would be expected for fully coupled explosions of 7.6 and 76.8 tons, and at near-source distances (<10 km) can be modeled well by reducing ground-motion predictions from the Fuis et al. (2001) model by a factor of 4. The results from the Sayarim explosions, combined with past and future experimental datasets, will lead to an improved understanding of the seismo-acoustic source function for explosions and energy partitioning between seismic and acoustic waves.

Ezersky M.,Geophysical Institute of Israel | Legchenko A.,CIRAD - Agricultural Research for Development
Geomorphology | Year: 2014

The Dead Sea (DS) coastal areas have been dramatically affected by sinkhole formation since around 1990. Such sinkholes along both Israeli and Jordanian shores are linked to karst cavities that form through slow salt dissolution. A quantitative estimate of such in-situ salt karstification would be an important indicator of sinkhole hazard. One of the indications of salt karstification is its increased hydraulic conductivity, caused by the development of dissolution cavities forming conducting channels within the salt layer. We measured the hydraulic conductivity (K) versus shear-wave velocity (Vs) of DS salt in situ for estimating the actual salt karstification in areas of sinkhole development. These parameters were measured with the Magnetic Resonance Sounding (MRS) and Multichannel Analysis of Surface Waves (MASW) methods, respectively. Understanding of the field relationships was augmented by similar inter-relations obtained in the laboratory on samples of DS salt. In-situ salt velocities Vs vary from 750m/s to over 1650m/s, while hydraulic conductivity (K) in the same zones varies between about 10-4m/s to slightly over 10-8m/s. Both field and laboratory K and Vs values fit the exponential function ln(K)=-0.0045*Vs-5.416 with a determination coefficient (R2) of 0.88. A classification based on Vs and K was generated for salt conditions and the corresponding degrees of sinkhole hazard, which was verified in the Mineral Beach sinkhole development area. The mapping of sinkhole sites shows that they form within highly conductive zones with K≥5.5*10-5. It is suggested that this methodology, with some modification, can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards. © 2014 Elsevier B.V.

Kaviani A.,Goethe University Frankfurt | Hofstetter R.,Geophysical Institute of Israel | Rumpker G.,Goethe University Frankfurt | Weber M.,Helmholtz Center Potsdam
Journal of Geophysical Research: Solid Earth | Year: 2013

Shear waveforms from core-refracted (SKS) phases recorded at 105 portable stations belonging to the DESERT and DESIRE campaigns and nine permanent broadband stations of the Israel Seismological Network are analyzed to study polarization seismic anisotropy beneath the region of the Dead Sea Transform fault in the Middle East. Shear wave splitting parameters exhibit variations with back azimuth (initial polarization) of the incoming SKS waves. The pattern of this variation is nearly constant along the strike of the fault suggesting a laterally uniform anisotropic structure beneath the Dead Sea region. The modeling of the azimuthal variations of the shear wave splitting parameters and split waveforms yields two-layered anisotropic models consisting of an upper layer with nearly N-S symmetry axis and a deeper layer with around N25°E symmetry axis. The split time is almost equally partitioned between the upper and lower layers allotting a value of 0.6-0.8 s to each layer. 2-D finite difference modeling across the southern segment of the Dead Sea Transform fault demonstrates that anisotropic structure in the strike-normal direction is relatively uniform. The Dead Sea Transform fault appears not to have a significant role in the development of the regional anisotropic fabric. The upper anisotropic layer is possibly related to a fossil fabric in the lithosphere, inherited from the Precambrian Pan-African Orogeny. The lower layer may be related to the mantle deformation due to the relative motion between the lithospheric plates and the asthenosphere and possibly affected by the local flow field due to mantle plumes as inferred by other studies. ©2013. American Geophysical Union. All Rights Reserved.

Kim S.G.,Korea Seismological Institute | Gitterman Y.,Geophysical Institute of Israel
Pure and Applied Geophysics | Year: 2013

The underwater explosion (UWE) resulting in the sinking of the South Korean warship, ROKS Cheonan occurred on March 26 2010. Raw data was analyzed from several 3-component stations-Baengyeong-do Korea Meteorological Administration (KMA) station (BAR), Ganghwa KMA station (GAHB), Incheon Incorporated Research Institutions for Seismology (IRIS) station (INCN), the short-period station-Deokjeok-do KMA station (DEI), as well as from the seismo-acoustic array Baengyeong-do Korea Institute of Geoscience and Mineral Resources (KIGAM) station (BRDAR). The ROKS Cheonan incident has been investigated by both the Multinational Civilian-Military Joint Investigation Group (Ministry of National Defense, 2010) and Hong (Bull Seism Soc Am 101:1554-1562, 2011). Their respective methods and conclusions are also presented in this study. One of the main differences between their findings and ours is that we deducted that the fundamental bubble frequency was 1.01 Hz with a subsequent oscillation of 1.72 Hz. Also, in contrast to findings by the MCMJIG and Hong, our analysis shows the first reverberation frequency to be 8.5 Hz and the subsequent one to be ≈25 Hz. The TNT-equivalent charge weight (seismic yield) and seismic magnitude were estimated from an observed bubble frequency of 1.01 Hz and the analytical model of a bubble pulse. From the data analyzed, we deducted that the seismic yield would be about 136 kg of TNT, which is equivalent to the individual yield of a large number of land control mines (LCM) which were abandoned in the vicinity of the ROKS Cheonan incident by the Republic of Korea (ROK) Navy in the 1970s (Ministry of National Defense 2010). Also, whereas both the MCMJIG and HONG estimated the local magnitude at 1.5, our findings came to the conclusion of a local magnitude of approximately 2.04 based on the bubble frequency of 1.01 Hz measured on the vertical component of BAR station data considering the empirical relationship between charge weight (TNT yield) and underwater explosion magnitude. Strong high-frequency signals collected at the 3-component BAR station approximately 30 s after P-wave arrivals and infrasound records at BRDAR clearly indicate powerful acoustic phases and N-waves caused by a relatively shallow UWE. T-phases are also observed on seismograms and spectra at 15-17 Hz on the DEI, GAHB, and INCN stations. © 2012 Springer Basel AG.

Loading Geophysical Institute of Israel collaborators
Loading Geophysical Institute of Israel collaborators