The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
N N Biswas - One of the best experts on this subject based on the ideXlab platform.
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stress pattern in the double Seismic Zone beneath cook inlet south central alaska
Tectonophysics, 1997Co-Authors: Natalia A Ratchkovsky, Jose Pujol, N N BiswasAbstract:Abstract Relocation of south-central Alaskan earthquakes recorded by the regional seismograph network, using the joint hypocenter determination method, revealed a double Seismic Zone in the underthrusting Pacific plate beneath the Cook Inlet area. The lower Zone is separated from the upper one by a decrease in Seismic activity within a 5–10 km wide band, and extends from a depth of 50 km to about 90 km. Stress tensor inversion for earthquakes in the upper and lower Zones shows different stress regimes. In the upper Zone minimum principal stress is oriented in the down-dip direction and maximum principal stress is normal to the Wadati-Benioff Zone (WBZ). In the lower Zone both maximum and minimum principal stresses are horizontal and rotated by 40–60° from the down-dip direction of the WBZ. Below 80–90 km depth, stress tensor inversion results show down-dip orientation of the minimum principal stress and the maximum stress aligned in the direction of convergence of Pacific plate.
Christine A Powell - One of the best experts on this subject based on the ideXlab platform.
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crustal and upper mantle velocity structure in the vicinity of the eastern tennessee Seismic Zone based upon radial p wave transfer functions
Journal of Geophysical Research, 2015Co-Authors: Jordan H Graw, Christine A Powell, Charles A LangstonAbstract:TeleSeismic transfer function analysis is used to investigate crust and upper mantle velocity structure in the vicinity of the active eastern Tennessee Seismic Zone (ETSZ). The ETSZ is associated with the New York-Alabama (NY-AL) magnetic lineament, a prominent aeromagnetic anomaly indicative of Grenville-age, basement structure. Radial component, P wave transfer functions for 10 short-period stations operated by the Center for Earthquake Research and Information are inverted for velocity structure. Velocity profiles are also determined for three broadband stations by converting the instrument response to that of an S-13 short-period seismometer. Distinct differences in the velocity profiles are found for stations located on either side of the NY-AL magnetic lineament; velocities west of the lineament are lower than velocities to the east of the lineament in the upper 10 km and in the depth range 30 to 50 km. A gradational Moho boundary is found beneath several stations located in the Valley and Ridge province. A Moho boundary is absent at four Valley and Ridge stations located east of the magnetic lineament and south of 35.5°N.
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crustal velocity structure associated with the eastern tennessee Seismic Zone vp and vs images based upon local earthquake tomography
Journal of Geophysical Research, 2014Co-Authors: Christine A Powell, Gordana Vlahovic, Mitchell Withers, Randel Tom Cox, Pierre ArroucauAbstract:We present three-dimensional P and S wave velocity models for the active eastern Tennessee Seismic Zone (ETSZ) using arrival time data from more than 1000 local earthquakes. A nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters. We image several velocity anomalies that persist through most of the inversion volume. Some anomalies support the presence of known features such as an ancient rift Zone in northern Tennessee. Other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies. We image a narrow, NE-SW trending, steeply dipping Zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent New York-Alabama magnetic lineament. The low-velocity Zone may have an apparent dip to the SE at depths exceeding 15 km. The low-velocity Zone is interpreted as a major basement fault juxtaposing Granite-Rhyolite basement to the NW from Grenville southern Appalachian basement to the SE. Relocated hypocenters align in near-vertical segments suggesting reactivation of a distributed Zone of deformation associated with a major strike-slip fault. We suggest that the ETSZ represents reactivation of an ancient shear Zone established during formation of the super continent Rodinia.
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a statistical analysis of earthquake focal mechanisms and epicenter locations in the eastern tennessee Seismic Zone
Bulletin of the Seismological Society of America, 1997Co-Authors: Martin C. Chapman, Christine A Powell, Gordana Vlahovic, M S SibolAbstract:Abstract The location and orientation of possible seismogenic basement faults in the eastern Tennessee Seismic Zone is studied using information provided by focal mechanisms and the location of earthquake epicenters. Twenty-six well-constrained focal mechanism solutions are derived using a new velocity model and relocated hypocenters. The results suggest that strike-slip motion on steeply dipping planes is the dominant mode of faulting throughout the 300-km-long Seismic Zone. Most of the mechanisms can be grouped into two populations. The larger population is characterized by steeply dipping N-S- and E-W-striking nodal planes with right-lateral and left-lateral slip, respectively. The second population differs from the first by an approximate 45° eastward rotation about the B axis. An analysis of the distribution of azimuths between epicenters was conducted. The frequency distribution of interevent azimuths shows significant clustering in the northeasterly and easterly directions, for interevent epicentral distances less than 30 km. Those directions represent the most often observed nodal plane orientations and are interpreted as the dominant strike directions of seismogenic basement faults. The locations of potential faults are inferred on the basis of statistically significant alignments of juxtaposed epicenters and correlation with focal mechanisms. The results suggest a series of northeast-trending, en-echelon basement faults, intersected by several east-trending faults. Most of the larger magnitude, instrumentally located, earthquakes in the Seismic Zone occurred in proximity to the statistically identified potential faults.
Michael W Hamburger - One of the best experts on this subject based on the ideXlab platform.
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evidence of possible induced Seismicity in the wabash valley Seismic Zone from improved microearthquake locations
Bulletin of the Seismological Society of America, 2006Co-Authors: Kevin C Eagar, Gary L Pavlis, Michael W HamburgerAbstract:To evaluate the spatial structure of Seismicity in the Wabash Valley of southern Indiana and Illinois, we analyzed data from a temporary Seismic network that included 10 three-component, short-period seismometers and a 10-component dense phased array. We produced the first comprehensive catalog of local earth- quakes recorded during the 211-day deployment, from November 1995 through June 1996. The results are dominated by a cluster of 534 microearthquakes, with magni- tudes ranging from 0.6 to 1.8, near the town of New Harmony, Indiana, that were detected and recorded only by the phased array. The remarkable similarity of the cluster events in terms of waveform, magnitude, and temporal distribution suggests a tightly spaced grouping from a single Seismic source. We relocated the earthquakes using improved relative arrival times of P and S waves computed by time-domain cross-correlation of the vertical beam traces and by complex cross-correlation of the horizontal beam traces, respectively. Additional constraints on absolute locations were applied using a graphical method of arrival-time difference analysis for six earthquakes recorded by two network stations outside the phased array. The resulting locations define a tight spatial grouping about a Zone of post-Paleozoic faulting just west of the Indiana-Illinois border, in White County, Illinois. Average source depths from phased-array location methods and waveform modeling with synthetic seis- mograms indicate, in contrast to larger events in the region, that the earthquakes occurred at depths less than 4 km, within the sedimentary section of the Illinois Basin. We propose that these earthquakes are artificially induced events, likely related to water injection for the purpose of secondary recovery of petroleum in the Illinois Basin. The primary evidence for this includes: (1) tight spatial clustering of earth- quakes; (2) unusually shallow earthquake depths; (3) good spatial correlation of the relocated hypocenters to existing wells and oil fields; and (4) highly repetitive events with only a small range in magnitude.
Syed Tallataf Hussain Shah - One of the best experts on this subject based on the ideXlab platform.
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structure of crust and upper mantle beneath nw himalayas pamir and hindukush by multi scale double difference Seismic tomography
Physics of the Earth and Planetary Interiors, 2018Co-Authors: Zahid Imran Bhatti, Junmeng Zhao, Nangyal Ghani Khan, Syed Tallataf Hussain ShahAbstract:Abstract The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep Seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional Seismic stations from 1950 to 2017. The northward dipping Seismic Zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian plate under the Hindukush beyond 71°E longitude. The Indian plate overturns due south after interacting with the Asian plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian plate. The Asian plate is also imaged as a southward subducting Seismic Zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale Seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.
Seth Stein - One of the best experts on this subject based on the ideXlab platform.
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triggering of new madrid Seismicity by late pleistocene erosion
Nature, 2010Co-Authors: Eric Calais, Andrew M Freed, R B Van Arsdale, Seth SteinAbstract:The New Madrid Seismic Zone, in a now heavily populated area of the central United States, was responsible for the 1811–12 New Madrid earthquakes of magnitudes of 7 or greater. The extent of the current Seismic hazard in the region is hotly debated. Eric Calais and colleagues present evidence that the geologically recent sequence of large earthquakes in this region was triggered by the rapid removal of sediments by the rivers of the northern Mississippi embayment at the end of the last ice age. Models indicate that fault segments that have already ruptured are unlikely to fail again soon, but stress changes from sediment unloading and previous earthquakes may eventually be sufficient to bring to failure other nearby segments that have not yet ruptured, indicating that the hazard may be more widespread than previously thought. These authors argue that the concentration of magnitude-7 or larger earthquakes in the New Madrid Seismic Zone since the end of the last ice age results from the recent, climate-controlled, erosional history of the northern Mississippi embayment. They show that the upward flexure of the lithosphere caused a reduction of normal stresses in the upper crust sufficient to unclamp pre-existing faults close to failure equilibrium. The spatiotemporal behaviour of earthquakes within continental plate interiors is different from that at plate boundaries. At plate margins, tectonic motions quickly reload earthquake ruptures, making the location of recent earthquakes and the average time between them consistent with the faults’ geological, palaeoSeismic and Seismic histories. In contrast, what determines the activation of a particular mid-continental fault and controls the duration of its Seismic activity remains poorly understood1. Here we argue that the concentration of magnitude-7 or larger earthquakes in the New Madrid Seismic Zone of the central United States2,3 since the end of the last ice age results from the recent, climate-controlled, erosional history of the northern Mississippi embayment. We show that the upward flexure of the lithosphere caused by unloading from river incision between 16,000 and 10,000 years ago caused a reduction of normal stresses in the upper crust sufficient to unclamp pre-existing faults close to failure equilibrium. Models indicate that fault segments that have already ruptured are unlikely to fail again soon, but stress changes from sediment unloading and previous earthquakes may eventually be sufficient to bring to failure other nearby segments that have not yet ruptured.
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time variable deformation in the new madrid Seismic Zone
Science, 2009Co-Authors: Eric Calais, Seth SteinAbstract:New geodetic measurements show that the New Madrid is currently deforming too slowly, if at all, to account for large earthquakes in the region over the past 5000 years. This result, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicates that either tectonic loading rates or fault properties vary over a few thousand years.
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tectonic implications of the gps velocity field in the northern adriatic region
Geophysical Research Letters, 2005Co-Authors: Gyula Grenerczy, Seth Stein, Giovanni Sella, Ambrus KenyeresAbstract:[1] Continuous and episodic GPS observations between 1991 and 2004 show that Adria moves independently of both stable Eurasia and Nubia. Adria moves NNE at 3–4.5 mm/yr increasing from N to S relative to Eurasia and may be fragmenting along the Gargano-Dubrovnik Seismic Zone. The observed 2–3 mm/yr of N-S Adria-Eurasia convergence is taken up by contraction across a narrow (∼70 km) Zone in the Eastern Alps and concomitant extrusion of the Alpine-North Pannonian unit. The Adria-Central Dinarides boundary is a broader collisional Zone with intense 1–1.5 mm/yr shortening near shore and 2 mm/yr spread across the Dinarides. The remaining 1–2 mm/yr motion E of the Alps and NE of the Dinarides is absorbed by the inverted contracting Pannonian basin leaving no significant deformation above 0.5 mm/yr in the Western and Northern Carpathians, and European Platform.
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dependence of possible characteristic earthquakes on spatial sampling illustration for the wasatch Seismic Zone utah
Seismological Research Letters, 2005Co-Authors: Seth Stein, Anke M Friedrich, Andrew V NewmanAbstract:An important issue for regional tectonics and earthquake hazard estimation is whether large earthquakes are “characteristic”, more frequent than would be inferred from the rates of smaller events. A challenge in resolving this question is that the rates of small earthquakes are typically determined from the seismologically recorded earthquake history, whereas the rates of large earthquakes are inferred from paleoSeismic observations. As a consequence, different results from comparing the two can arise depending on the specific assumptions made and time and space sampling used. In general, earthquake recurrences approximately follow a log-linear, b -value, or Gutenberg-Richter relation, log N = a - bM , with b ∼1, such that the logarithm of the annual number ( N ) of earthquakes above a given magnitude ( M ) decreases linearly with magnitude (Ishimoto and Iida, 1939; Gutenberg and Richter, 1944). Studies of specific areas, however, which commonly address the short history of seismological observations by combining seismological data for smaller earthquakes with paleoSeismic data or geologic inferences for larger earthquakes, sometimes infer that large “characteristic” earthquakes occur more frequently than expected from the log-linear frequency-magnitude relation observed for smaller earthquakes (Schwartz and Coppersmith, 1984). Whether characteristic earthquakes are real or apparent in any given region is an interesting question (Kagan, 1996; Wesnousky, 1996). A number of effects can give rise to apparent characteristic earthquakes or “uncharacteristic” earthquakes, ones that appear to occur less frequently than expected from the rates of smaller earthquakes (Stein and Newman, 2004). One bias can result from a short recorded earthquake history, in particular if its length is comparable to the mean recurrence time of large earthquakes predicted by a Gutenberg-Richter distribution. A second bias can result from errors in estimating the size or frequency of the largest earthquakes from the paleoSeismic record (Stein and Newman, 2004; …
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slow deformation and lower Seismic hazard at the new madrid Seismic Zone
Science, 1999Co-Authors: A V Newman, Seth Stein, John Weber, Joseph F Engeln, Timothy H DixonAbstract:Global Positioning System (GPS) measurements across the New Madrid Seismic Zone (NMSZ) in the central United States show little, if any, motion. These data are consistent with platewide continuous GPS data away from the NMSZ, which show no motion within uncertainties. Both these data and the frequency-magnitude relation for Seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8, their recurrence interval should well exceed 2500 years, longer than has been assumed. Alternatively, the largest 1811 and 1812 earthquakes and those in the paleoSeismic record may have been much smaller than typically assumed. Hence, the hazard posed by great earthquakes in the NMSZ appears to be overestimated.
