Seismic evidence of conjugate normal faulting: The 1994 Devil Canyon earthquake sequence near Challis, Idaho

Jackson, Suzette M.

doi:10.2172/10191368

Cited by 3 publications

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References 13 publications

(21 reference statements)

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“…In some cases, these antithetic faults are marked by discontinuous scarps of low relief. The structure of faults exposed in mines [Wallace and Morris, 1986;Hudson, 1993] and seismological studies of multiple-event earthquakes and aftershock sequences provide corroborative evidence for the existence of these complex fault structures at depth [Doser, 1985;Wesnousky, 1988;Jackson, 1994]. In this paper we define and discuss two-dimensional, crosssectional models of simple fault systems typical of those found in half-grabens from around the world.…”

Section: Introductionmentioning

confidence: 93%

“…Two types of secondary fault geometry are common and amenable to two-dimensional analysis: (1) subsidiary, antithetic faults that intersect the master fault at depth (Figure 1 a), and (2) y-shaped fault sets formed by synthetic splay faults that dip in the same direction as the master fault (Figure 1 a). Antithetic and splay faults may penetrate deep into the seismogen•c crust [Doser, 1985;Barrientos et al, 1987;Westaway, 1992;Jackson, 1994] or, alternatively, may form at shallow depth where there is a strong mechanical interaction with the Earth's surface (Figure l a). Such fault geometries may have only limited strike length (few kilometers) so that a two-dimensional model based on a cross section is only an approximation of the natural structure.…”

Section: Structure Of Half-grabensmentioning

confidence: 99%

“…Typical antithetic scarp heights described in reports and mapping notes are 20-30% or less than those measured along the master fault scarps, which is broadly consistent with the boundary element model predictions for both listric and planar fault systems. Antithetic scarps are much more laterally discontinuous than the master fault scarps, probably due in part to poor preservation because of the relatively small surface offsets, and perhaps because antithetic faults are shorter and less connected along strike than faults in the master fault zone, Italy (Ms 7.0) earthquake; and the 1984 Devils Canyon, Idaho (ML 5.8) earthquake[Jackson, 1994]. In each case, rupturing on the main fault was followed within minutes to weeks by rupturing on conjugate faults dipping antithetic to the main fault Jackson [1994].…”

mentioning

confidence: 99%

“…Antithetic scarps are much more laterally discontinuous than the master fault scarps, probably due in part to poor preservation because of the relatively small surface offsets, and perhaps because antithetic faults are shorter and less connected along strike than faults in the master fault zone, Italy (Ms 7.0) earthquake; and the 1984 Devils Canyon, Idaho (ML 5.8) earthquake[Jackson, 1994]. In each case, rupturing on the main fault was followed within minutes to weeks by rupturing on conjugate faults dipping antithetic to the main fault Jackson [1994]. studied the Devils Canyon, Idaho, earthquake sequence by detailed monitoring of aftershocks using a Fault geometry and earthquake sequence reported byJackson [1994] for the Devils Canyon earthquake sequence in the Lost River fault zone, Idaho.…”

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confidence: 99%

“…In each case, rupturing on the main fault was followed within minutes to weeks by rupturing on conjugate faults dipping antithetic to the main fault Jackson [1994]. studied the Devils Canyon, Idaho, earthquake sequence by detailed monitoring of aftershocks using a Fault geometry and earthquake sequence reported byJackson [1994] for the Devils Canyon earthquake sequence in the Lost River fault zone, Idaho. Dashed line added beneath the ML 5.8 main shock to indicate a possible extension of the Challis fault segment at depth.…”

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confidence: 99%

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Geometry and slip distribution in normal fault systems: Implications for mechanics and fault‐related hazards

Bruhn¹,

Schultz²

1996

J. Geophys. Res.

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Normal faults are important sources of large, destructive earthquakes in continental rift provinces. We investigate the mechanical characteristics of multiple, linked master and subsidiary faults using two‐dimensional boundary element models. The master fault system is a Coulomb‐frictional fault that dips 50° from the surface to a depth of 15 km, where it is linked to a subjacent shear zone that creeps under low resolved shear stress. We consider two basic configurations, one in which the shear zone and master fault are coplanar, and the other in which the shear zone dips 20°, forming a bent or crudely listric fault system. Antithetic and splay faults are added to the master fault system in each case to model failure of multiple fault systems that are typical of half‐grabens. We focus on the mechanical interactions between the various faults in order to identify points of initial failure, spatial variations in the amount of fault slip, and the patterns of surface deformation that may precede catastrophic failure of the master fault system. In all cases, failure on the master frictional fault initiates at the base, where it joins the creeping shear zone, and at the Earth's surface during the same stress increment. The listric fault system fails at lower regional differential stress than the planar fault system. Failure of a large antithetic fault that dips at 70° from the surface to the base of the frictional master fault initiates at lower regional differential stress for the listric than for the planar case. Several repeated failure episodes may be required to cause surface offset on the antithetic fault if the master fault system is planar, but antithetic surface faulting may occur during each master fault failure episode in the listric case. Modeled splay faults dip from the surface at either greater (70°) or lower (50°) angles than the frictional master fault to a depth of 5 km, where they intersect the master fault. In both cases, surface slip is greater on the master fault and lesser on the splay fault. Surface deformation prior to catastrophic failure of the frictional master fault is generated by creep on the deep‐seated shear zone and during the initial stages of master fault rupture. Footwall uplift is predicted above a steeply dipping, locked Coulomb fault and creeping shear zone, but the footwall uplift is absent in the listric fault ‐ shear zone case. A localized zone of increased extensional strain is centered on the surface trace of the master fault as the result of near‐surface extensional and shear fracturing during the initial stages of fault slip. These geodetic anomalies are of interest because they are a near‐surface phenomenon which may also alter fluid flow and gas flux and be detectable by hydrologic and geochemical instrumentation as well as geodetic measurements.

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Section: Introductionmentioning

confidence: 93%

Section: Structure Of Half-grabensmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Geometry and slip distribution in normal fault systems: Implications for mechanics and fault‐related hazards

Bruhn¹,

Schultz²

1996

J. Geophys. Res.

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Analysis of broadband records from the 28 June 1992 Big Bear earthquake: Evidence of a multiple-event source

Jones

Hough

1995

Bulletin of the Seismological Society of America

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The 28 June 1992 Big Bear earthquake occurred at 15:05:21 GMT and is considered to be an aftershock of the earlier Mw = 7.3 Landers earthquake. From overall aftershock locations and long-period focal studies, rupture is generally assumed to have propagated northeast. No surface rupture was found, however, and the mainshock locations determined from both strong motion and TERRAscope data are mutually consistent and do not lie on the assumed fault plane. Further, directivity analysis of records from the TERRAscope array suggests significant short- and long-period energy propagating northwest along the presumed antithetic fault plane. This observation is supported by significant early aftershocks distributed along both the presumed rupture plane and the antithetic plane to the northwest. An empirical Green's function (eGf) approach using both the Mw = 5.2, 28 June 1992 14:43 GMT foreshock and the Mw = 5.0 17 August 1992 aftershock produces consistent results and suggests that the Big Bear event comprised at least two substantial subevents. From the eGf results, we infer that the second and possibly a third subevent occurred on the presumed (northeast striking) mainshock rupture surface, but that significant moment release occurred on the antithetic northwest striking surface. We present results from line-source fault modeling of broadband displacement recordings of the Big Bear mainshock, which indicate that a two-fault event is necessary to produce the observed waveforms. The limitations imposed by the mainshock location and directivity analysis require that the initial rupture be towards the northwest, striking 320°. This was followed approximately 4 sec later by bilateral rupture along a northeast-southwest fault that strikes 50° east of north.

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Geological field trips in southern Idaho, eastern Oregon, and northern Nevada

Wood¹

2005

Open-File Report

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We reconstructed equilibrium-line altitudes for late-Pleistocene glaciers in eastern Oregon, central and northern Idaho, and western Montana. Over 500 cirque to small valley glaciers were mapped where moraines and other evidence for ice margins could be confidently interpreted on digital topographic maps. Equilibrium-line altitudes (ELAs) were estimated using the accumulation-area ratio method. Spatial patterns of ELAs show a strong correspondence to present-day precipitation patterns. Modern dry regions have relatively high ELAs (e.g., 2,600-2,900 m at about lat 44.5°N. in the Lost River and Lemhi Ranges south-central Idaho), whereas wetter regions at similar latitudes have considerably lower ELAs (e.g., 2000-2200 m in mountains southwest of McCall, Idaho). Steep eastward increases in ELAs across larger massifs such as the Wallowa, Sawtooth, and central Bitterroot Mountains reflect orographic effects on westerly flow. The Columbia River basin of eastern Washington and Oregon provided a lowland corridor for moist, eastward-moving Pacific airmasses, producing anomalously low ELAs in bordering ranges (e.g., <1,800 m around lat 46.5°N. in the Clearwater River drainage of northern Idaho currently the wettest region of the study area). Smaller-scale features such as the Salmon and Payette River canyons also appear to have acted as conduits for atmospheric moisture. Overall, the ELA data point strongly toward a moisture source in the north Pacific Ocean. General circulation climate model results indicate that at the last continental glacial maximum, an anticyclone centered over the continental ice sheets and southward deflection of the jet stream should produce dry conditions in the interior northwestern United States. Our results suggest that the anticyclone is weaker than in some previous simulations, and easterly winds are not clearly indicated across the study region. By 15 ka, northward retreat and decline in continental ice-sheet elevation caused contraction of the anticyclone, and winter westerlies from the north Pacific continued to strengthen across the study area until 12 ka. An associated increase in snowfall may have allowed more precipitation-sensitive mountain glaciers to remain near their maxima or expand during the post-late glacial maximum period, before the dramatic warming into the early Holocene. Similar positions and topography of continental ice sheets during buildup prior to the late glacial maximum also might promote glacial advances by focusing strong westerly flow on mountain ranges of the interior northwest. Further dating of mountain glacier advances is necessary to test these hypotheses.

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Seismic evidence of conjugate normal faulting: The 1994 Devil Canyon earthquake sequence near Challis, Idaho

Abstract: Portions of this document may be illegible in electronic image products. images are produced from the best avaiiabfe original document. The thesis presented by Suzette M. Jackson entitled SEISMIC EVIDENCE OF

Cited by 3 publications

References 13 publications

Geometry and slip distribution in normal fault systems: Implications for mechanics and fault‐related hazards

Geometry and slip distribution in normal fault systems: Implications for mechanics and fault‐related hazards

Analysis of broadband records from the 28 June 1992 Big Bear earthquake: Evidence of a multiple-event source

Geological field trips in southern Idaho, eastern Oregon, and northern Nevada

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