crustal structure and geological structure in Shaanxi Province. Based on the regularity of past large earthquakes, we propose that the next M 7 intermediate-depth earthquake can be expected to occur in Vrancea at a depth interval of 140-160 km sometime early in this century. The depth obtained is approximately 140 kilometers, the seismic moment, 0.8 1027 dyne-cm and the mechanism from both data sets is very similar to that of the previous 1940 and 1977 Vancrea events, indicating that these events, although having occurred at noticeably different depths, are expressions of the same tectonic process. For any Earth model, accounting for a constant phase shift as a function of azimuth makes the depth and moment tensor determination very stable and in particular removes the possible trade-off between source time and depth as well as biases on the depth determination that could arise from poor modelling of propagation effects. Bulletin of the Geological Society of Greece. H��UKn�0���M�۠�*��m��IG�j�����s�"�3�OÙy�bSV�MYh�d�x���[������ -�_w�T.X�_���2r Ggr"D�7;�+�U�f9�/�VwӇ�r��.��d�C$$*B�OTl9Әs8F��4�UMJQ���n�V. Areas to the west and east of the rCFB were undergoing continent-continent collisions in the same time. (1994) can also be used to explain observed waveforms in an extended azimuthal range from 105° to 243° and is valid for earthquakes having different hypocentral locations in the deep Vrancea seismic zone. On the basis of the examples presented, it is shown how the, We determine the source time histories of five recent (1994-1996) large, deep-focus earthquakes using a method that inverts for fault slip from far-field moment rate functions. The Vrancea seismic zone, located beneath the ``elbow'' of the Eastern and Southern Carpathians, is characterized by intermediate-depth seismicity associated with subduction and plate collision. 0000006847 00000 n The final hypocenter positions together with the P- and S-wave block velocities support the tectonic model for the Vrancea seismic region of Fuchs et al (1979), with the correction that the intermediate seismic events occur at the limit of separation between the gravitationally sinking slab and the rest of the now inactive NE-SW subduction.-from Author Center of Earth Phys & Seismol, PO Box MG-2 Bucharest-Magurele, Roumania. The results may be interpreted in terms of a complex source model in which rupture starts at a small asperity and then triggers the larger scale rupture of a neighbouring prestressed patch. A number of seventy-five fault-plane solutions given by the present authors for earthquakes having occurred during the last 50 years in Europe, Asia Minor and Northern Africa and twenty-six solutions due to other authors are studied from the point of view of the geometry, kinematics and dynamics of the faulting process.The main results, entered in Table 1 and plotted on Figs. More stable, A method is proposed to determine the source process time of large earthquakes using mantle Rayleigh wave spectral data. -from Authors. The break-off ran eastwards along the whole Carpathian arc, from the Early Miocene, to its present position in the bend between the East and South Carpathians. P-wave arrival times from a set of 119 local events occurred in the Vrancea region were used in a simultaneous inversion for hypocenters and 3-D velocity structure. Poisson ratio in the north of Weihe Basin has higher values than those in the south. A multi-iterative hypocenter location was performed at each step in the velocity iteration process. Large gaps in the slip distributions point to possible occurrence on multiple fault planes. ... 28, see Table 1) with the H R V D mechanism. Small-scale heterogeneities like the subducted lithosphere in the Hellenic collision zone were imaged in the region with the highest density of wave paths, which indicates an optimum resolution of better than 200 km. These results are of particular significance for seismic hazard studies, and specifically for the estimation of future strong motions. The only unbroken area is at a depth of 140-160 km, which we current consider to be a seismic gap. The major intermediate shocks exhibit a quite stable reverse faulting focal mechanism with the rupture plane oriented in a NE–SW direction, parallel to the Carpathians arc. The subducted oceanic lithosphere possibly trends northeast and dips either vertically [Roman, 1970] or at a steep angle of about 60 ø. 0000004782 00000 n P��S@@�0yH�����/�|q�)��� ��f ����:C�����6�"c�%0�rZcg�@k�P���ָ�jM�.,)F�Ɔ\6�dD(a2"�X�ۏ,��UF`t��1� �s$M�9?p�R��/'SN���{�k�d�� @�w�:G����tmͥQWb��f��V�8N�p�[AE�Q3��C)�D�ž����&ϫ�/heIp��;��fo�v�n+�JX�fM|����?����H��L�'�'�(�q���no-���K�����C�tá�� (1979), Räkers and Müller (1982) and Iosif et al. The fundamental Rayleigh mode, which at high frequencies is more prone to scattering and multipathing, was generally low passed at 25 mHz. Previous studies of the most recent strong intermediate-depth earthquakes (1940 November 10, M w = 7.7; 1977 March 4, M w = 7.4; 1986 August 30, M w = 7.1; 1990 May 30, M w = 6.9) based on teleseismic data have indicated static stress drop values around 10 MPa, and source durations in the range 3–10 s (for example, Räkers & Müller 1987; - Modeling wave propagation for soil structure interaction 0000004044 00000 n However, our modelling also reveals highly ambiguous amplitude variations of PcP and a reflection off the top of the anomaly for various ULVZs and topography models. Therefore, its help with plate geometry determination is limited. Access scientific knowledge from anywhere. Following, the moment magnitude Mw, which is considered to be the most reliable magnitude scale, was determined. 0000007607 00000 n Subduction setting was characterized by steep dip of the subducting slab, strong hinterland extension, extensive areal magmatism in the hinterland and asthenospheric upwelling in the hinterland. Body waves were fit for frequencies up to 60mHz. H��Uю�0�����t��m�^���]�N��4_S�� ���@�fwfv6٤ O�d%�"�&�]����P��dWmh��l>�;�����|Nv?7���+D��ޫ���e����ѻ��iF�X@��C{{r��.fKt H�|V�n�@����J�2��ͻ}��i*���ժU^�����_ߵ���X������9gf�$��BU�D&o�a����蚄 Earthquake Engineering Research Institute. Main scope of the study is the determination of a. Title: The Romanian earthquake of August 30, 1986: A study based on GEOSCOPE ve ry long-period and broadband data Created Date: Mon Nov 29 11:19:06 2004 0000009134 00000 n Comparing the present results with previous ones, based on a smaller number of earthquakes, (Tables 2 and 3) shows a better agreement of the European pattern of earthquake mechanisms with the world pattern for all earthquakes. Measured by the size of the country, earthquakes occur rather rarely. One of the most important features is a high-velocity body existing beneath the Carpathian arc at depths between 100 and 170 km. The observed velocity contrast across the TTZ is largest between the Pannonian Basin and the Russian Platform, where it is equal to 12 per cent at 80 km depth. The small size (about 80 km in length and 40 km in width) and geometry of the seismic zone have made it difficult to interpret the kinematics of subduction and continental collision in the Romanian Carpathians. %PDF-1.3 %���� -from Authors, Journal of Geophysical Research Atmospheres. The Weihe Basin with frequent earthquakes locates in a compound position of several tectonic systems. 0000002501 00000 n The model is derived from the inversion of the waveforms of 217 seismograms, using the partitioned waveform-inversion method for the seismogram in the time window from the S-wave arrival to the fundamental mode of the Rayleigh wave. 0000006702 00000 n A total of 7837 P and 2292 S arrival times from 433 shallow and intermediate-depth earthquakes recorded by local and regional seismic stations were inverted for the three-dimensional (3-D) seismic velocity structure.