Seismic Interpretation of the Deep Structure of the Wabash Valley Fault System

Bear, Glenn W.; Rupp, John A.; Rudman, Albert J.

doi:10.1785/gssrl.68.4.624

Cited by 40 publications

(13 citation statements)

References 24 publications

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“…Sexton et al (1986) proposed from seismic-reflection profiles that a small, latest Precambrian-Early Cambrian rift, the Grayville graben, underlies part of the Wabash Valley fault system. Bear et al (1997) interpreted 30 published and mostly proprietary seismic-reflection profiles to improve the definition of the Grayville graben. Bear et al found evidence of Cambrian extensional slip on the four faults that are labeled in Figure 3.…”

Section: Grayville Grabenmentioning

confidence: 99%

“…It was not well enough characterized to be included in the 1996 maps, but Bear et al (1997) provided sufficient evidence to warrant adding the graben to the continental rim for the 2002 maps. Despite the lack of significant Cambrian offset in the northern and southern ends of the graben (Hildenbrand and Ravat, 1997;Bear et al, 1997), for the purpose of the 2002 maps we suggest representing the graben as including the entire mapped extents of the AlbionRidgway, Herald-Phillipstown, and New Harmony fault zones and the Inman East Fault. We suggest this because any Phanerozoic rifting of the basement may indicate seismic potential higher than that of a craton that lacks known Phanerozoic rifts (Johnston, 1989(Johnston, , 1994.…”

Section: Grayville Grabenmentioning

confidence: 99%

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Updated Seismic Hazard in the Southern Illinois Basin: Geological and Geophysical Foundations for Use in the 2002 USGS National Seismic-hazard Maps

Wheeler

Cramer

2002

Seismological Research Letters

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East of the Rocky Mountain front, recurrence intervals of most large earthquakes are long compared to the historical earthquake record. Information about longer-term, prehistoric earthquake histories can reduce the resulting uncertainty in hazard assessments. Accordingly, paleoseismological results and selected aspects of bedrock geology, such as the boundary between the craton and adjacent Phanerozoic terranes, were incorporated into the 1996 USGS national seismic-hazard maps to extend the total record of seismicity back into prehistory. We identify post-1996 findings that should be incorporated during updating of the central U.S. part of the 1996 maps for publication in 2002. A companion paper (Cramer et al., 2002) determines the impact of each new finding on the calculated hazard. We propose three adjustments to the largest moment magnitude, M(max), that is assumed to occur within a specified area. (1) Throughout the slightly active central craton of the central and eastern United States, paleoseismological evidence from the Illinois basin and global seismological evidence require that M(max) be increased above the value of M 6.5 assumed for the 1996 maps, to M 7.0. (2) We recommend increasing M(max) from M 6.5 to M 7.5 within the Rough Creek graben of western Kentucky and southeastern Illinois, the Rome trough in eastern Kentucky, and the Grayville graben of Illinois and Indiana. The increases would achieve geological and logical consistency with M(max) values in other parts of the central and eastern U.S. (3) Two prehistoric earthquakes of estimated M 7.1 and M 7.5 near the Illinois-Indiana border occurred within the craton. Absent evidence to justify raising the cratonic M(max) to 7.5, we specify a zone surrounding the two prehistoric earthquakes where M(max) could be locally raised to M 7.5.

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Section: Grayville Grabenmentioning

confidence: 99%

Section: Grayville Grabenmentioning

confidence: 99%

Updated Seismic Hazard in the Southern Illinois Basin: Geological and Geophysical Foundations for Use in the 2002 USGS National Seismic-hazard Maps

Wheeler

Cramer

2002

Seismological Research Letters

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“…Reflection surveys have identified possible blind thrust faults at 20-25 km depth that are oriented roughly north-south (Bear et al, 1997;McBride et al, 2002). The m b 5.5 southern Illinois earthquake (Langer and Bollinger, 1991), which had a focal depth of 22-25 km, is interpreted by McBride et al (2002) to have occurred on this type of fault.…”

Section: Geologic Settingmentioning

confidence: 99%

Wagon Loads of Sand Blows in White County, Illinois

Hough

Bilham

Mueller

et al. 2005

Seismological Research Letters

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“…Sexton et al (1986) argued that the faults of the WVFS developed by reactivation of a Precambrian rift zone that was a northern extension of the Reelfoot-Rough Creek system, based on the interpreted continuity of gravity and magnetic anomaly patterns (Braile et al, 1982). Bear et al (1997), however, concluded that the fault system is not a northward continuation of the Reelfoot rift because fault displacements of the WVFS decrease southward in the direction of the rift complex. Nelson and Lumm (1987) and Hildenbrand and Ravat (1997) also concluded that the WVFS does not cross the Rough Creek-Shawneetown fault zone ( Figure 2).…”

Section: Regional Settingmentioning

confidence: 99%

“…This gradient also corresponds to the northwestern margin of a gravity low along the CGL ( Figure 4A). The upper -1.8 s of the record, discussed in detail by Bear et al (1997) and Potter et al (1997), is a layered sequence of nearly horizontal reflections that correspond to the well known Paleozoic strata of the Illinois basin. The WVFS is expressed as subtle offsets within the Paleozoic section ( Figure northwest-dipping reflections dominate.…”

Section: "Dip-parallel" Profiles (A and B)mentioning

confidence: 99%

Interpreting the Earthquake Source of the Wabash Valley Seismic Zone (Illinois, Indiana, and Kentucky) from Seismic-reflection, Gravity, and Magnetic-intensity Data

McBride

Hildenbrand

Stephenson

et al. 2002

Seismological Research Letters

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Reprocessing of seismic-reflection data reveals new images of upper-to middle-crustal structures beneath the Wabash Valley seismic zone, located north of the New Madrid seismic zone within the seismically active southern Illinois basin. Four intersecting deep seismic profiles (243 km total) indicate an anomalous, 5-10-km-wide zone of dipping reflections and diffractions below the western flank of the Wabash Valley fault system (WVFS). The zone corresponds in places to gently arched regions of Paleozoic strata. The reflector zone can be interpreted as a result of either (or a combination of) magmatic intrusion or structural deformation. The area encompassing the reflection profiles has experienced several moderate magnitude (3.0 _< mbLg_~< 5.5) earthquakes during the past 50 years, defining the central part of the Wabash Valley seismic zone. The hypocenter of the largest 20th-century earthquake in the central USA midcontinent (9 November 1968, mbLg 5.5) corresponds to the most prominent zone of dipping middle-crustal reflections, just west of the WVFS. Both the focal mechanism (moderately dipping reverse fault) and the expected rupture zone size (-2.9 km fault length) of this earthquake are consistent with the orientation and size of observed reflectors. Dipping reflector patterns in the Precambrian crust are not collinear with fault surfaces updip in the Paleozoic sedimentary section. This indicates that shallow Paleozoic structures are effectively "decoupled" from deeper, possibly seismogenic structure, which suggests that understanding Paleozoic structure is not the key to understanding the earthquake source. The complex dipping crustal reflectivity beneath the WVFS is typical of Paleozoic continental convergent zones observed elsewhere (e.g., Appalachian orogen) and thus may suggest a preserved Proterozoic suture, possibly associated with the distal Grenville orogeny or an older event.Although magnetic intensity, Bouguer gravity, and seismic-reflection data present different means of understanding the deep geology of the area, their integration aids in limiting the number of admissible interpretations. The reflection profiles indicate a variable zone of anomalous crustal structure, including the dipping reflector zone, along a trend of northeast-trending gravity and magnetic highs locally defining the Commerce geophysical lineament (CGL), which is a suspected source of seismic hazard in the central USA midcontinent. Three-dimensional inverse modeling of the residual isostatic gravity anomaly values indicates that the upper part of the dipping reflector zone beneath the CGL lies near an important density boundary in the upper Precambrian crust. The results of our study suggest that the seismogenic source just north of the New Madrid seismic zone consists, in part, of a pre-existing fabric of blind thrusts localized along preexisting igneous intrusions, locally coincident with the CGL. This suggests that the CGL may be seismogenic in places and thus a potential seismic hazard. The variation in the expression of ...

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Seismic Interpretation of the Deep Structure of the Wabash Valley Fault System

Cited by 40 publications

References 24 publications

Updated Seismic Hazard in the Southern Illinois Basin: Geological and Geophysical Foundations for Use in the 2002 USGS National Seismic-hazard Maps

Updated Seismic Hazard in the Southern Illinois Basin: Geological and Geophysical Foundations for Use in the 2002 USGS National Seismic-hazard Maps

Wagon Loads of Sand Blows in White County, Illinois

Interpreting the Earthquake Source of the Wabash Valley Seismic Zone (Illinois, Indiana, and Kentucky) from Seismic-reflection, Gravity, and Magnetic-intensity Data

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