Regenerate faults of small Cenozoic offset as probable earthquake sources in the southeastern United States

Wentworth, Carl M.; Mergner-Keefer, Marcia

doi:10.3133/ofr81356

Cited by 14 publications

(9 citation statements)

References 35 publications

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“…For instance, previous studies (e.g. Wentworth and Mergner-Keefer, 1983;Kafka, 2000;Talwani and Schaeffer, 2001) have suggested that (blind) reverse faults potentially capable of slipping in future earthquakes are widespread in the eastern USA. Such faults, oriented as indicated in Figure 7, can potentially experience slip triggered by seaonal transients in lower-crustal flow following major storms.…”

Section: Discussionmentioning

confidence: 99%

“…However, the NE-SW elongation of isoseismals ( Figure 12) suggests its strike, the macroseismic location placing this earthquake within a network of reverse faults where microseismicity indicates a NE-SW or ENE-WSW maximum principal stress (see, e.g., Talwani, 1982Talwani, , 1999Weems and Lewis, 2002). Analysis of microearthquake locations and focal mechanisms, drilling, seismic reflection profiling and aeromagnetic survey suggests that the most important active structures are steeply dipping oblique (right-lateral) reverse faults striking NE-SW or NNE-SSW, with the inland block being upthrown (see, e.g., Hamilton et al, 1983;Wentworth and Mergner-Keefer, 1983;Talwani, 1993, 2000). The most important of these appears to be the NW-dipping Summerville Fault (Figure 12), a re-activated Mesozoic normal fault.…”

Section: The Eastern Usamentioning

confidence: 99%

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Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Westaway

2006

Earth Surf Processes Landf

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Many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over Quaternary timescales. On the basis of the rheological knowledge gained, it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust. This view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation. It is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity, and by instances of seasonal seismicity that correlates with seasonal climate. Human interference in the environment can affect surface loading: for instance, deforestation for agriculture or urban development can cause increased erosion rates; global warming is expected to cause increased storminess (and thus increased erosion rates) and/or global sea-level rise. The possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment.Surface processes as a cause of intraplate seismicity Figure 1. (a) Graph of estimated temperature T against depth z for the Palaeozoic continental crust beneath the Atlantic Coastal Plain (ACP) of South Carolina. Calculations use T , e.g., Lachenbruch, 1970), where T 0 is the mean surface temperature, K is the thermal conductivity of the crust, A 0 and D are the surface radiogenic heat production and its scale depth, and q 0 is the heat flow at the base of the lithosphere. T 0 is set to 20°C (cf. Bollinger et al., 1985). Values of K (3·29 W m −1°C−1 ) and A 0 (2·70 µW m −3 ) are from the borehole at Springfield, SC, ~150 km NW of Charleston. D = 8 km (typical for the ACP); q 0 is set to 48·5 mW m −2 (close to the 48·2 mW m −2 typical for the ACP) to give the observed surface heat flow at Springfield of 70·1 mW m −2 . All these geothermal data are from Costain et al. (1986). This calculated geotherm roughly matches the local ~15 km depth limit of seismicity (with 90 per cent of events shallower than 13 km), which is thought to represent thẽ 300°C isotherm (see, e.g., Bollinger et al., 1985), and indicates a Moho temperature (for 35 km depth) of 588°C. Extrapolated, it predicts the ~1400°C asthenosphere temperature at ~90 km depth, a conservative value given the ~80 km lithosphere thickness from seismic tomography (van der Lee, 2002). (b) Predicted variation of viscosity η with depth z across this lower crust, which from (a) is taken as spanning 15-35 km depth. η is calculated as η = η L exp(G/RT) (Westaway, 1998), where R is the molar gas constant (8·3143 J K −1 mol −1 ) and T(z) is the temperature predicted at each depth in (a). G (150 kJ mol −1 ) and η L (6·67 × 10 7 Pa s) parametrize the lower-crustal rheology (see Table I). Figure 2.Diagram illustrating an eroding region that provides the sediment source for an adjacent depocentre, with isost...

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Section: Discussionmentioning

confidence: 99%

Section: The Eastern Usamentioning

confidence: 99%

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Westaway

2006

Earth Surf Processes Landf

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“…Knowledge of the in-situ stress field is invaluable for assessing seismic hazards in areas such as the eastern United States with a relatively low level of seismicity and where major active faults have not been identified. Results of previous studies (Zoback and Zoback, 1980;Yang and Aggarwal, 1981;and Wentworth and Mergner-Keefer, 1983) suggested that a zone of NW-oriented compression exists along the Atlantic seaboard of the U.S. in contrast to the NE-to ENE-oriented maximum horizontal compressive stresses found throughout much of the midcontinent region of North America (Sbar and Sykes, 1973;Zoback and Zoback, 1980;M. L. Zoback and others, 1986).…”

Section: Introductionmentioning

confidence: 93%

Principal stress directions on the Atlantic continental shelf inferred from the orientations of borehole elongations

Dart¹,

Zoback²

1987

Open-File Report

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“…However, Obermeier and others (1985) and Talwani and Cox (1985) have documented the occurrence of at least two prehistoric earthquakes in the past 3,000 yr that produced sandblows at a site that also produced sandblows in 1886. The frequency of large Holocene earthquakes that is implied by the sandblow observations appears to be substantially higher than the frequency of large earthquakes implied by post-Late Cretaceous deformation (e.g., Wentworth and Mergner-Keefer, 1983). In the last several thousand years, the South Carolina region may have been in a time of high seismicity, anomalous with respect to the Cenozoic as a whole, similar to that suggested for the Mississippi Embayment (see the section on the Mississippi Embayment).…”

Section: South Carolina Coastal Plainmentioning

confidence: 63%

“…19) have been viewed as possibly seismogenic (Wentworth and Mergner-Keefer, 1983) because they have experienced late Cenozoic displacements (Mixon and Newell, 1977). (Dutton, 1889), and epicenters of recent instrumentally recorded earthquakes (Dewey, 1983;Tarr and Rhea, 1983).…”

Section: Middle Atlantic Statesmentioning

confidence: 99%

Chapter 25: Earthquakes, faults, and the seismotectonic framework of the contiguous United States

Dewey

Hill²,

Ellsworth³

et al. 1989

Geological Society of America Memoirs

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Recent decades have seen dramatic improvement in the ability of earth scientists to resolve the geometries of earthquake sources and to relate these geometries to local and global tectonic processes. Well-studied seismogenic faults consist of individual segments that are offset from each other along strike or that have different strikes. The boundaries between segments help control or limit rupture propagation during large earthquakes. On many segments of the plate-bounding San Andreas fault system, fault orientation and structure at depth are well represented by the surface fault trace. In the Cordillera away from the San Andreas system, faults that have produced large earthquakes seem commonly to be expressed at the surface by traces that are distorted representations of the faults at depth. In the United States east of the Cordillera, it has not been possible to associate earthquakes with geologically mapped faults as directly as in the western United States. The following observations, however, suggest that many eastern earthquakes occur on reactivated pre-Cenozoic faults: (1) epicenters in some sources coincide with mapped pre-Cenozoic faults; (2) in other sources, planar zones of hypocenters and instrumentally inferred fault planes parallel regional structural trends; and (3) some pre-Cenozoic faults show Cenozoic displacement. Global tectonic models have been extended to account for the distribution and focal depths of earthquakes that occur in California away from the principal plate boundary and to account for the orientations of regional stress tensors east of the plate boundary. Plate-tectonic models have also led to the hypothesis that a large thrust-interface earthquake might someday occur in the Pacific Northwest subduction zone, notwithstanding the absence of such earthquakes in the historic record. on July 26, 2015 memoirs.gsapubs.org Downloaded from Earthquakes, faults, and seismotectonic framework, U.S. 543 95 90 85 80 75 70 65the Geological Society of America, Decade of North American Geology (DNAG), seismicity map of North America (Engdahl and Rinehart, 1988), using the same conventions to assign magnitudes to plotted events. Where more than one earthquake has been assigned to the same epicenter (to within 4 km), only a single symbol for the largest earthquake is plotted. on July 26, 2015 memoirs.gsapubs.org Downloaded from on July 26, 2015 memoirs.gsapubs.org Downloaded fromEarthquakes, faults, and seismotectonic framework, U.S. 545North American plates in the Pacific Northwest is a subject of controversy; it, too, may be a temporary quiescence, or it may reflect aseismic subduction.The seismicity of the United States east of the Cordillera, though much lower on average than that of the Cordillera and Pacific Coast, is nonetheless important as an indicator of midplate tectonic processes and as a potential hazard to human beings. The largest historic earthquakes in the central and eastern United States had magnitudes greater than 6.5 and probably involved fault rupture through tens of kilomete...

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Regenerate faults of small Cenozoic offset as probable earthquake sources in the southeastern United States

Cited by 14 publications

References 35 publications

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Principal stress directions on the Atlantic continental shelf inferred from the orientations of borehole elongations

Chapter 25: Earthquakes, faults, and the seismotectonic framework of the contiguous United States

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