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Seismic Records (seismic + record)
Selected AbstractsSystem identification applied to long-span cable-supported bridges using seismic recordsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2008Dionysius M. Siringoringo Abstract This paper presents the application of system identification (SI) to long-span cable-supported bridges using seismic records. The SI method is based on the System Realization using Information Matrix (SRIM) that utilizes correlations between base motions and bridge accelerations to identify coefficient matrices of a state-space model. Numerical simulations using a benchmark cable-stayed bridge demonstrate the advantages of this method in dealing with multiple-input multiple-output (MIMO) data from relatively short seismic records. Important issues related to the effects of sensor arrangement, measurement noise, input inclusion, and the types of input with respect to identification results are also investigated. The method is applied to identify modal parameters of the Yokohama Bay Bridge, Rainbow Bridge, and Tsurumi Fairway Bridge using the records from the 2004 Chuetsu-Niigata earthquake. Comparison of modal parameters with the results of ambient vibration tests, forced vibration tests, and analytical models are presented together with discussions regarding the effects of earthquake excitation amplitude on global and local structural modes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Swarms of microearthquakes associated with the 2005 Vulcanian explosion sequence at Volcán de Colima, MéxicoGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010Vyacheslav M. Zobin SUMMARY The swarms of microearthquakes, that appeared at Volcán de Colima, México before and after its large 2005 Vulcanian explosions, are discussed. The study of 966 microearthquakes is based on the seismic records of short-period seismic station EZV4 situated at a distance of 1.7 km from the crater. Three samples of microearthquakes were selected: the seismic records associated with a single 2005 September 16 large explosion, and the seismic records associated with two sequences of large explosions, the 2005 March 10 and 13 explosions and the 2005 May 30 and June 2, 5 and 7 explosions. These explosions were seven of 15 large explosions (E, 1011 J) that occurred during the 2005 explosive sequence. The microearthquake waveforms were identified as the records of rockfalls and microexplosions. The explosive microearthquakes represent from 84 to 89 per cent of the total number of microearthquakes with the readable waveforms. The dominant frequencies of the explosive microearthquakes were 2.8 Hz for the 2005 March explosion sequence and 2005 September 16 explosion, and 1.3, 2.0 and 2.8 Hz for the 2005 May-June explosion sequence. Energy of microexplosions that generated the microearthquake waveforms ranged from 104 to 7 × 107 J. The force component, corresponding to the largest microexplosive events, was estimated at a level from 3.1 × 107 to 3.6 × 108 N. The appearance of microearthquakes before large volcanic explosions and the sharp increase in their rate of appearance some hours before an explosion makes them a useful instrument for volcano monitoring. [source] SUPRACENTER: Locating fireball terminal bursts in the atmosphere using seismic arrivalsMETEORITICS & PLANETARY SCIENCE, Issue 9 2004W. N. EDWARDS A computer program, SUPRACENTER, calculates travel times by ray tracing through realistic atmospheres (that include winds) and locates source positions by minimization of travel time residuals. This is analogous to earthquake hypocenter location in the solid Earth but is done through a variably moving medium. Inclusion of realistic atmospheric ray tracing has removed the need for the simplifying assumption of an isotropic atmosphere or an approximation to account for "wind drift." This "drift" is on the order of several km when strong, unidirectional winds are present in the atmosphere at the time of a fireball's occurrence. SUPRACENTER-derived locations of three seismically recorded fireballs: 1) the October 9, 1997 El Paso superbolide; 2) the January 25, 1989 Mt. Adams fireball; and 3) the May 6, 2000 Morávka fireball (with its associated meteorite fall), are consistent with (and, probably, an improvement upon) the locations derived from eyewitness, photographic, and video observations from the respective individual events. If direct acoustic seismic arrivals can be quickly identified for a fireball event, terminal burst locations (and, potentially, trajectory geometry and velocity information) can be quickly derived, aiding any meteorite recovery efforts during the early days after the fall. Potentially, seismic records may yield enough trajectory information to assist in the derivation of orbits for entering projectiles. [source] Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North SeaBOREAS, Issue 3 2010ALASTAIR G. C. GRAHAM Graham, A.G.C., Lonergan, L. & Stoker, M.S. 2010: Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea. Boreas, Vol. 39, pp. 471,491. 10.1111/j.1502-3885.2010.00144.x. ISSN 0300-9483. Geological constraints on ice-sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here, we present a detailed interpretation of depositional environments from a new 30-m-long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British,Fennoscandian Ice Sheet. Seven units characterize a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeoregimes. These are: a period of advance and ice-sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine-to-marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overriding by the SE,NW-flowing Witch Ground ice stream. AMS 14C dating confirms ice-stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 14C ka BP. Sediments overlying the ice-compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 14C ka BP. A re-advance of British ice during the last deglaciation, dated at 13.9 14C ka BP, delivered ice-proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally pervasive iceberg-ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 14C ka BP, and may correspond to oscillating ice-sheet margins during final, dynamic ice-sheet decay. [source] Late- and postglacial history of the Great Belt, DenmarkBOREAS, Issue 1 2004OLE BENNIKE On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200,300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP. [source] | ||||||||||