On the geoelectric structure of major strike-slip faults and shear zones

Unsworth, Martyn; Bedrosian, Paul A.

doi:10.1186/bf03353337

Cited by 56 publications

(24 citation statements)

References 39 publications

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“…5 is likely linked to shear deformation of the DST in the middle and lower crust and related processes. High conductivities in active tectonic zones have often been associated with fluids and hydrous minerals (Boerner et al 1998;Unsworth & Bedrosian 2004;Jones et al 2005;Ritter et al 2005;Wannamaker 2005;Becken et al 2011;Meqbel et al 2014). For instance, Becken et al (2011) interpreted a subvertical conductive anomaly extending through the entire crust northwest of Parkfield in California as a migration path for deep (partly mantle derived) fluids into the San Andreas Fault system.…”

Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

“…Ritter et al 2003Ritter et al , 2005Unsworth & Bedrosian 2004;Tank et al 2005;Thiel et al 2009;Becken et al 2011;Desissa et al 2013). The geometry and the overall conductance of FZCs depend on local geological, hydrogeological conditions and the geodynamic (tectonic) setting of a fault (see Unsworth & Bedrosian 2004;Ritter et al 2005, and references therein.). Ritter et al (2003) interpreted MT data collected along a profile across the Araba fault (a segment of the DST) which is located ∼150 km to the south of the DSB.…”

Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

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Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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S U M M A R YWe report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid-to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above-mentioned off-profile features.

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Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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“…At the Parkfield segment of the strike‐slip SAF, a granitic basement is overlain by sedimentary cover to the west and the conductive Franciscan melange to the east. Low‐resistivity structures are clearly seen to be coincident with the SAF zone at both PKD and SAO [ Unsworth and Bedrosian , 2004]. Such variations in conductivity are thought to be controlled by variations in fluid saturation and fracturing.…”

Section: Introductionmentioning

confidence: 99%

Long‐term monitoring of ULF electromagnetic fields at Parkfield, California

2010

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[1] Electric and magnetic fields in the (10 −4 -1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California, from 1995. A data window (2002-2005, enclosing the 28 September 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields or changes in ground conductivity occurred before the earthquake. The data were edited, removing intervals of instrument malfunction, leaving 875 days in the 4 year period. Frequent, spikelike disturbances were common but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signal-to-noise amplitude spectra, estimated via magnetotelluric processing, showed the behavior of the ultralow frequency fields to be remarkably constant over the period of analysis. These first-order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the "residual" fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies present in both the electric and magnetic fields from those present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed, suggesting local distortion due to variations in near-surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects were found that can be reasonably characterized as precursors to the Parkfield earthquake.

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“…Crustal structure in the fault zones is often characterized by low resistivity1234567891011121314151617181920212223 that indicates crustal fluid and suggests a possible relation to earthquake generation. The North Anatolian Fault zone (NAFZ), northwestern Turkey, is characterized by the low resistivity structure and electromagnetic studies there are expected to provide important information on the relation of crustal fluid to earthquake generation.…”

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confidence: 99%

Rapid changes in the electrical state of the 1999 Izmit earthquake rupture zone

et al. 2013

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Crustal fluids exist near fault zones, but their relation to the processes that generate earthquakes, including slow-slip events, is unclear. Fault-zone fluids are characterized by low electrical resistivity. Here we investigate the time-dependent crustal resistivity in the rupture area of the 1999 Mw 7.6 Izmit earthquake using electromagnetic data acquired at four sites before and after the earthquake. Most estimates of apparent resistivity in the frequency range of 0.05 to 2.0 Hz show abrupt co-seismic decreases on the order of tens of per cent. Data acquired at two sites 1 month after the Izmit earthquake indicate that the resistivity had already returned to pre-seismic levels. We interpret such changes as the pressure-induced transition between isolated and interconnected fluids. Some data show pre-seismic changes and this suggests that the transition is associated with foreshocks and slow-slip events before large earthquakes.

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On the geoelectric structure of major strike-slip faults and shear zones

Cited by 56 publications

References 39 publications

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Long‐term monitoring of ULF electromagnetic fields at Parkfield, California

Rapid changes in the electrical state of the 1999 Izmit earthquake rupture zone

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