A lithospheric model to interpret focal properties of intermediate and shallow shocks in central greece     

B. C. Papazachos 《Pure and Applied Geophysics》1977,115(3):655-666

Summary An attempt has been made to interpret the striking difference, in focal properties, between the intermediate and shallow earthquakes in Central Greece and an observed time sequence of these shocks by a lithospheric model. This model consists of a lithospheric slab descending from the Ionian to the Aegean and a back-arc expanding Aegean lithosphere. Thrust faulting near the top surface of the slab, caused by the sinking of the slab, triggers spreading and normal faulting in the back-arc Aegean region.  相似文献   

Spatial Distribution of Time-independent Seismicity in China     

C. Qin  E. E. Papadimitriou  B. C. Papazachos  G. F. Karakaisis 《Pure and Applied Geophysics》1999,154(1):101-119

—The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using three complete samples of earthquakes which occurred during the last two centuries (1800–1995). The b value of the Gutenberg-Richter relation was estimated by using this data sample. Taking into account the fact that the b value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposing on the entire area studied, and their distribution was examined. The results showed that the b value increases smoothly from 0.4 in inner-Mongolia to 0.8 in the east, south and southwest of China with higher values (b>0.8) in the Taiwan region. Furthermore, keeping fixed the obtained b values, the a value distribution was also examined. In order to display more detailed information about the seismicity, smaller cell surface (10,000 km²) for the calculation of the a values was chosen. The mean return periods for different cutoff magnitudes were also calculated for each of these small cells. It was observed that the mean return periods are the shortest ones in China, which are 10 and 50 years for the magnitude larger than or equal to 6.0 and 7.0, respectively.  相似文献   

An algorithm for fast 3D inversion of surface electrical resistivity tomography data: application on imaging buried antiquities     

N.G. Papadopoulos  P. Tsourlos  C. Papazachos  G.N. Tsokas  A. Sarris  J.H. Kim 《Geophysical Prospecting》2011,59(3):557-575

In this work a new algorithm for the fast and efficient 3D inversion of conventional 2D surface electrical resistivity tomography lines is presented. The proposed approach lies on the assumption that for every surface measurement there is a large number of 3D parameters with very small absolute Jacobian matrix values, which can be excluded in advance from the Jacobian matrix calculation, as they do not contribute significant information in the inversion procedure. A sensitivity analysis for both homogeneous and inhomogeneous earth models showed that each measurement has a specific region of influence, which can be limited to parameters in a critical rectangular prism volume. Application of the proposed algorithm accelerated almost three times the Jacobian (sensitivity) matrix calculation for the data sets tested in this work. Moreover, application of the least squares regression iterative inversion technique, resulted in a new 3D resistivity inversion algorithm more than 2.7 times faster and with computer memory requirements less than half compared to the original algorithm. The efficiency and accuracy of the algorithm was verified using synthetic models representing typical archaeological structures, as well as field data collected from two archaeological sites in Greece, employing different electrode configurations. The applicability of the presented approach is demonstrated for archaeological investigations and the basic idea of the proposed algorithm can be easily extended for the inversion of other geophysical data.  相似文献   

Travel times of P_n -waves in the Aegean and surrounding area     

D. G. Panagiotopoulos  B. C. Papazachos 《Geophysical Journal International》1985,80(1):165-176

Summary. Based on accurately located 23 very shallow earthquakes ( h = 1–14 km) in northern and central Greece by portable networks of seismic stations and by the joint epicentre method, the travel times of the P_n -waves from the foci of these earthquakes to the sites of 54 permanent stations in the Balkan region have been determined. The travel times of P_n -waves in the central and eastern part of the area (eastern Greece, south-eastern Yugoslavia, the Aegean Sea, Bulgaria, southern Romania, western Turkey) fit a straight line very well with the P_n velocity equal to 7.9 ± 0.1 km s^-1. On the contrary, the travel times of P_n -waves to stations in the western part of the area (Albania, western Greece) do not fit this curve because the P_n -waves travelling to these stations are delayed by more than 1 s due to the thicker crust under the Dinarides–Hellenides mountain range. Time delays for P_n -waves have been calculated for each permanent station in the Balkan area with respect to the mean travel-time curve of these waves in the central and eastern part of the area. Corrections of the travel times for these delays contribute very much to the improvement of the accuracy in the location of the shallow earthquakes in the Aegean and surrounding area.  相似文献   

Tsunamis in and near Greece and their relation to the earthquake focal mechanisms     

B. C. Papazachos  P. P. Dimitriu 《Natural Hazards》1991,4(2-3):161-170

The major earthquake-induced tsunamis reliable known to have occurred in and near Greece since antiquity are considered in the light of the recently obtained reliable data on the mechanisms and focal depths of the earthquakes occurring here. (The earthquake data concern the major shocks of the period 1962–1986.) First, concise information is given on the most devastating tsunamis. Then the relation between the (estimated) maximum tsunami intensity and the earthquake parameters (mechanism and focal depth) is examined. It is revealed that the most devastating tsunamis took place in areas (such as the western part of the Corinthiakos Gulf, the Maliakos Gulf, and the southern Aegean Sea) where earthquakes are due to shallow normal faulting. Other major tsunamis were nucleated along the convex side of the Hellenic arc, characterized by shallow thrust earthquakes. It is probably somewhere there (most likely south of Crete) that the region's largest known tsunami occurred in AD 365, claiming many lives and causing extensive devastation in the entire eastern Mediterranean. Such big tsunamis seem to have a return period of well over 1000 years and can be generated by large shallow earthquakes associated with thrust faulting beneath the Hellenic trench, where the African plate subduces under the Euroasian plate. Lesser tsunamis are known in the northernmost part of the Aegean Sea and in the Sea of Marmara, where strike-slip faulting is observed. Finally, an attempt is made to combine the tsunami and earthquake data into a map of the region's main tsunamigenic zones (areas of the sea bed believed responsible for past tsunamis and expected to nucleate tsunamis in the future).  相似文献   

Long-term earthquake prediction in the circum-pacific convergent belt     

B. C. Papazachos  E. E. Papadimitriou  G. F. Karakaisis  D. G. Panagiotopoulos 《Pure and Applied Geophysics》1997,149(1):173-217

Investigation of the time-dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering (duration extending to several years) which follow a power-law time distribution. Mainshocks, however (interevent times of the order of decades), show a quasiperiodic behaviour and follow the ‘regional time and magnitude predictable seismicity model’. This model is expressed by the following formulas $$\begin{gathered} \log T_t = 0.19 M_{\min } + 0.33 M_p - 0.39 \log m_0 + q \hfill \\ M_f = 0.73 M_{\min } - 0.28 M_p + 0.40 \log m_0 + m \hfill \\ \end{gathered} $$ which relate the interevent time,T _t (in years), and the surface wave magnitude,M _f , of the following mainshock: with the magnitude,M _min, of the smallest mainshock considered, the magnitude,M _p , of the preceded mainshock and the moment rate,m ₀ (in dyn.cm.yr^?1), in a seismogenic region. The values of the parametersq andm vary from area to area. The basic properties of this model are described and problems related to its physical significance are discussed. The first of these relations, in combination with the hypothesis that the ratioT/T _t , whereT is the observed interevent time, follows a lognormal distribution, has been used to calculate the probability for the occurrence of the next very large mainshock (M _s ≥7.0) during the decade 1993–2002 in each of the 141 seismogenic regions in which the circum-Pacific convergent belt has been separated. The second of these relations has been used to estimate the magnitude of the expected mainshock in each of the regions.  相似文献   

Surface fault traces and fault plane solutions of the May–June 1978 major shocks in the Thessaloniki area, Greece.     

B. Papazachos  D. Mountrakis  A. Psilovikos  G. Leventakis 《Tectonophysics》1979,53(3-4)

It is shown that the foci of the recent earthquakes in the Thessaloniki area of northern Greece are located in an arcuate seismic zone which is associated with the Serbomacedonian geologic zone. Three main lines of fracture have been observed in the epicentral area after the May–June 1978 earthquakes. Field and macroseismic observations as well as fault plane solutions for the main shock and for the largest foreshock show that both earthquakes are due to a strike slip sinistral motion with a small reverse component on a steeply dipping and trending southeast-northwest fault.  相似文献   

Dependence of the seismic parameterb on the magnitude range     

B. C. Papazachos 《Pure and Applied Geophysics》1974,112(6):1059-1065

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Small-scale spatial variation of the stress field in the back-arc Aegean area: Results from the seismotectonic study of the broader area of Mygdonia basin (N. Greece)     

D.A. Vamvakaris  C.B. Papazachos  E.E. Karagianni  E.M. Scordilis  P.M. Hatzidimitriou 《Tectonophysics》2006,417(3-4):249-267

In the present work a detailed seismotectonic study of the broader area of the Mygdonia basin (N. Greece) is performed. Digital data for earthquakes which occurred in the broader Mygdonia basin and were recorded by the permanent telemetric network of the Geophysical Laboratory of the Aristotle University of Thessaloniki during the period 1989–1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information. Fault plane solutions for the 3 main shocks of Volvi (23/05/78, M_W = 5.8 and 20/06/78, M_W = 6.5) and Arnaia (04/05/95, M_W = 5.8) events and the 1978 aftershock sequence were additionally used. Moreover, data from two local networks established in the Mygdonia basin were also incorporated in the final dataset.Determination of the stress field was realized by the use of the method of Gephart and Forsyth [Gephart, J.W., Forsyth, D.W., 1984. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence: Jour. Geophys. Res., v.89, no. B11, p. 9305–9320] for the stress tensor inversion and the results were compared with independent estimates based on the calculation of the average moment tensor [Papazachos, C.B.,Kiratzi, A.A., 1992. A formulation for reliable estimation of active crustal deformation and its application to central Greece. Geophys. J. Int. 111, 424–432]. The obtained stress results show a relatively good agreement between the two approaches, with differences in the azimuth of the dominant extension axis of the order of 10°. Furthermore, comparison with independent information for the mean stress axes provided by the study of kinematics on neotectonic faults [Mountrakis, D., Kilias, A., Tranos, M., Thomaidou, E., Papazachos, C., Karakaisis, G., Scordilis, E., Chatzidimitriou, P., Papadimitriou, E., Vargemezis, G., Aidona, E., Karagianni, E., Vamvakaris, D. Skarlatoudis, A. 2003. Determination of the settings and the seismotectonic behavior of the main seismic-active faults of Northern Greece area using neotectonic and seismological data. Earthquake Planning and Protection Organisation (OASP) (in Greek)] shows a similar agreement with typical misfit of the order 10°. The stress inversion method was modified in order to select one or both nodal planes of the focal mechanism which corresponds to the “true” fault plane of the occurred earthquakes and was able to select a single fault plane in the majority of examined cases. Using this approach, the obtained fault plane rose diagrams are in agreement with results from various neotectonic studies. Moreover, several secondary active fault branches were identified, which are still not clearly observed in the field.  相似文献   

Surface fault traces,fault plane solution and spatial distribution of the aftershocks of the September 13, 1986 earthquake of Kalamata (Southern Greece)     

B. Papazachos  A. Kiratzi  B. Karacostas  D. Panagiotopoulos  E. Scordilis  D. M. Mountrakis 《Pure and Applied Geophysics》1988,126(1):55-68

A shallow earthquake ofM _S=6.2 occurred in the southern part of the Peloponnesus, 12 km north of the port of the city of Kalamata, which caused considerable damage. The fault plane solution of the main shock, geological data and field observations, as well as the distribution of foci of aftershocks, indicate that the seismic fault is a listric normal one trending NNE-SSW and dipping to WNW. The surface ruptures caused by the earthquake coincide with the trace of a neotectonic fault, which is located 2–3 km east of the city of Kalamata and which is related to the formation of Messiniakos gulf during the Pliocene-Quaternary tectonics. Field observations indicate that the earthquake is due to the reactivation of the same fault.A three-days aftershock study in the area, with portable seismographs, recorded many aftershocks of which 39 withM _S1.7 were very well located. The distribution of aftershocks forms two clusters, one near the epicenter of the main shock in the northern part of the seismogenic volume, and the other near the epicenter of the largest aftershock (M _S=5.4) in the southern part of this volume. The central part of the area lacks aftershocks, which probably indicates that this is the part of the fault which slipped smoothly during the earthquake.  相似文献