Synthesis of Recent Paleoseismic Research on Quaternary Faulting in the Eastern Tennessee Seismic Zone, Eastern North America: Implications for Seismic Hazard and Intraplate Seismicity

ABSTRACT Causes of intraplate seismicity remain a great unsolved problem, in contrast with plate-boundary seismicity. Modern seismicity records frequent seismic activity in plate-boundary seismic zones, but in fault zones where seismic activity is not frequent, plate boundary or intraplate, resolution of prehistoric earthquake activity is critical for estimating earthquake recurrence interval and maximum expected magnitude. Thus, documenting prehistoric earthquakes is crucial for assessing earthquake hazard posed to infrastructure, including nuclear reactors and large dams. The ∼400 km long eastern Tennessee seismic zone (ETSZ), United States, is the third most active seismic zone east of the Rocky Mountains in North America, although the largest recorded ETSZ earthquake is only Mw 4.8. Ironically, it is the least studied major eastern U.S. seismic zone. Recent ETSZ field surveys revealed an 80 km long, 060°-trending corridor containing northeast-striking Quaternary thrust, strike slip, and normal faults with displacements ≥1 m. It partially overlaps a parallel trend of seismicity that extends 30 km farther southwest, suggesting this active faulting zone may extend ∼110 km within part of the ETSZ. Near Dandridge, Tennessee, a thrust fault in French Broad River alluvium records two earthquakes in the last 40,000 yr. About 50 km southwest near Alcoa, Tennessee, a thrust fault cuts Little River alluvium and records two earthquakes between 15,000 and 10,000 yr ago. About 30 km farther southwest at Vonore, Tennessee, a thrust fault displaces bedrock ≥2 m over colluvium, and alluvium is normal faulted >2 m. This corridor, just west of the Blue Ridge escarpment, overlies a steep gradient in midcrustal S-wave velocities, consistent with a basement fault at hypocentral depths. The corridor faults may be connected to a basement fault or localized coseismic faults above a blind basement fault. Our current data suggest at least two Mw≥6.5 surface rupturing events in the last 40,000 yr.

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Seismic Reflection Expression of Reactivated Structures in the New Madrid Rift Complex

Seismological Research Letters ◽

10.1785/gssrl.59.4.141 ◽

1988 ◽

Vol 59 (4) ◽

pp. 141-150 ◽

Cited By ~ 1

Author(s):

John. L. Sexton

Keyword(s):

Seismic Reflection ◽

Structural Features ◽

Normal Faults ◽

Earthquake Activity ◽

Seismic Zone ◽

Reflection Method ◽

Intraplate Earthquakes ◽

Reflection Data ◽

Seismic Reflection Method ◽

New Madrid

Abstract An important aspect of seismogenesis concerns the role of preexisting faults and other structural features as preferred zones of weakness in determining the pattern of strain accumulation and seismicity. Reactivation of zones of weakness by present day stress fields may be the cause of many intraplate earthquakes. To understand the relation between reactivated structures and seismicity, it is necessary to identify structures which are properly oriented with respect to the present-day stress field so that reactivation can occur. The seismic reflection method is very useful for identifying and delineating structures, particularly in areas where the structures are buried as in the New Madrid seismic zone. Application of the seismic reflection method in widely separated locations within the New Madrid rift complex has resulted in successful detection and delineation of reactivated rift-related structures which are believed to be associated with earthquake activity. The purpose of this paper is to discuss results from seismic reflection profiling in the New Madrid rift complex. Reflection data from several surveys including USGS Vibroseis* surveys in the Reelfoot rift area reveal reactivated faults and other deep rift-related structures which appear to be associated with seismicity. High-resolution explosive and Mini-Sosie** reflection surveys on Reelfoot scarp and through the town of Cottonwood Grove, Tennessee, clearly show reverse faults in Paleozoic and younger rocks which have been reactivated to offset younger rocks. A Vibroseis survey in the Wabash Valley area of the New Madrid rift complex provides direct evidence for a few hundred feet of post-Pennsylvanian age reactivation of large-offset normal faults in Precambrian-age basement rocks. Several earthquake epicenters have been located in the vicinity of these structures. In the Rough Creek graben, Vibroseis reflection data provide clear evidence for reactivation of basement faults. The success of these reflection surveys shows that well-planned seismic reflection surveys must be included in any program seeking to determine the relationship between preexisting zones of weakness and seismicity of an area.

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Seismic activity and structural features in the Charlevoix region, Quebec

Canadian Journal of Earth Sciences ◽

10.1139/e87-202 ◽

1987 ◽

Vol 24 (11) ◽

pp. 2118-2129 ◽

Cited By ~ 21

Author(s):

Maurice Lamontagne

Keyword(s):

Seismic Activity ◽

Impact Crater ◽

Time Window ◽

Fault System ◽

Earthquake Risk ◽

Earthquake Activity ◽

Seismic Zone ◽

Nodal Solutions ◽

Data Set ◽

The Impact

The Charlevoix region is historically the most active earthquake zone in eastern Canada. Understanding the links between its seismicity and the faults of the region is important for the assessment of earthquake risk along the St. Lawrence Valley. The region has been monitored by a microseismic array since 1977, yielding accurate locations of the hypocentres. Previous analyses of data from the array indicated a relationship between the earthquakes and the St. Lawrence Valley paleorift faults. As a sequel to previous studies, the relationships between the seismic activity and the faults of the region were reexamined through the use of the composite P-nodal solutions, in an effort to clarify the nature of faulting in the seismic zone. The microseisms were partitioned into subsets of events on the basis of geological and hypocentre-trend considerations. The main objectives of this paper are to delineate the details of faulting within the Charlevoix region and to determine the effect of the impact crater on the nature of faulting in this area.Assuming a constant 6.2 km/s velocity model and using a data set of 107 events, composite fault-plane solutions were computed. The composite P-nodal solutions indicated that the Charlevoix impact crater modifies to a certain extent the focal-mechanism characteristics. Events outside the impact crater were found to be quite consistent in their polarity distribution on the focal sphere, suggesting similarity in their focal mechanisms. The composite mechanism of these events suggests a relationship between the earthquakes and the north–south faults mapped outside the impact crater. The magnitude mb (Lg) 5.0 earthquake of August 19, 1979, the largest event in the selected time window, had different fault planes than some of its aftershocks. Nevertheless, the polarity distribution of the aftershocks was in agreement with the average trend for the events outside the crater. Events inside the impact crater were found to be produced along more variable fault orientations, with an average trend similar to that of the rift fault system. It is proposed that the meteor impact weakened the rift faults and introduced its own fractures. The present earthquake activity probably occurs along these weak fault surfaces. The effect of the impact crater on the type of faulting versus depth is not readily discernible from available data. In general, meteor impacts do not leave neotectonic seismic signatures: the Charlevoix impact crater might represent a different case because of the presence of weakened paleorift faults.

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Distributed Neogene faulting across the western to central Arizona metamorphic core complex belt: Synextensional constriction and superposition of the Pacific–North America plate boundary on the southern Basin and Range

Geosphere ◽

10.1130/ges02036.1 ◽

2019 ◽

Vol 15 (4) ◽

pp. 1409-1435 ◽

Cited By ~ 2

Author(s):

John S. Singleton ◽

Nikki M. Seymour ◽

Stephen J. Reynolds ◽

Terence Vomocil ◽

Martin S. Wong

Keyword(s):

North America ◽

Plate Boundary ◽

Detachment Fault ◽

Normal Faults ◽

Core Complex ◽

The Pacific ◽

Complex Development ◽

Dextral Shear ◽

Extension Direction ◽

Central Arizona

Abstract We present fault data from a belt of Miocene metamorphic core complexes in western and central Arizona (USA) to determine patterns of brittle strain during and after large-magnitude extension, and to evaluate the magnitude of postextensional dextral shear across the region. In the White Tank Mountains, coeval WNW- to NW-striking dextral, normal, and oblique dextral-normal faults accommodated constrictional strain with extension subparallel to the direction of ductile stretching during core complex development. Northwest-striking oblique dextral-normal faults locally accommodated similar strain in the Harquahala Mountains, whereas in the South Mountains, constriction was primarily partitioned on NE-dipping normal faults and conjugate NW- and north-striking strike-slip faults. We interpret brittle constrictional strain to have developed during the late stages of large-magnitude extension associated with core complex development and folding of detachment fault corrugations. The oblique orientation of the Arizona core complex belt with respect to the extension direction likely resulted in a minor component of dextral transtension, accounting for much of the constrictional strain. In addition, far-field stresses associated with the transtensional Pacific–North America plate boundary may have contributed to constriction, which characterizes most Neogene detachment fault systems in the southwest Cordillera. Following cessation of detachment fault slip across the Arizona core complex belt (ca. 14–12 Ma), distributed NW-striking dextral and oblique dextral–NE-side-up (reverse) faults modified the topographic envelope of corrugations to an orientation clockwise of the core complex extension direction. Based on our analysis of this misalignment, we interpret the postdetachment fault dextral shear strain to increase northwestward from 0.03 across the South Mountains (0.5–0.6 km total slip across 18 km) to >0.03–0.07 across the Harquahala and Harcuvar Mountains (1.2–2.5 km of total slip across ∼35 km) and ∼0.2 across the Buckskin-Rawhide Mountains (7–8 km across 36 km). This along-strike variation in dextral shear is consistent with the regional pattern of distributed strain associated with the Pacific–North America plate boundary, as cumulative dextral offset in the lower Colorado River region increases toward the eastern Mojave Desert region to the northwest.

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THE TECTONIC SETTING OF THE OCTOBER 8 m 2005 EARTHQUAKE IN KASHMIR, NORTH PAKISTAN

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16646 ◽

2018 ◽

Vol 40 (1) ◽

pp. 463

Author(s):

E. Skourtsos ◽

E. Lekkas

Keyword(s):

Sedimentary Cover ◽

Tectonic Setting ◽

Hanging Wall ◽

Focal Depth ◽

Thrust Fault ◽

Normal Faults ◽

Seismic Zone ◽

Distinct Structure ◽

Seismic Fault ◽

Dip Angle

On the 8th of October 2005 an earthquake of magnitude 7.6 occurred in northern Pakistan. The earthquake epicenter was located in Pakistan Kashmir, 90 km north of Islamabad, the capital of Pakistan. The focal depth was 26 km triggered by a thrust fault striking NW-SE and of 40o dip angle towards the NE. The mean fault slip was estimated as 4 m. The aftershocks epicenters were located northeastwards of the Indus - Kohistan Seismic Zone. The structures that trace the activated fault were distributed along the southwestern limb of the Muzaffarabad anticline and grouped as structures of flexural-slip folding, structures that are correlated to folding and normal faults. The latter may represent overturned segments of the seismic fault on the high-angle limb of the Muzaffarrabad anticline. This anticline is located on the hanging wall of a thrust fault with geometry and kinematics characteristics similar to those of the Indus — Kohistan Seismic Zone. This zone, from the Hazara - Kashmir Syntaxis to the Swat River represents a blind thrust under the metamorphosed rocks of the Lower Himalayas, while in the region of Sub- Himalayas becomes a distinct structure. This thrust fault is linked in depth to the Main Himalaya Thrust through which, the cratonic basement of India is subducting under its sedimentary cover.

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Seismic expression of shallow structures in active tectonic settings in New Zealand

Exploration Geophysics ◽

10.1071/eg989287 ◽

1989 ◽

Vol 20 (2) ◽

pp. 287

Author(s):

C.D. Cape ◽

R.M. O'Connor ◽

J.M. Ravens ◽

D.J. Woodward

Keyword(s):

New Zealand ◽

Plate Boundary ◽

Accretionary Prism ◽

Seismic Profile ◽

Thrust Fault ◽

Strike Slip ◽

Normal Faults ◽

Thrust Faults ◽

Seismic Reflection Data ◽

Reflection Data

Late Cenozoic deformation along the Australian/Pacific plate boundary is seen in onshore New Zealand as zones characterised by extension- or transcurrent- or contraction-related structures. High-resolution multichannel seismic reflection data were acquired in several of these tectonic zones and successfully reveal the shallow structures within them. Thirty kilometres of dynamite reflection data in the Rangitaiki Plains, eastern Bay of Plenty, define a series of NE-trending normal faults within this extensional back-arc volcanic region. The data cross surface ruptures activated during the 1987 Edgecumbe earthquake. In the southern North Island, a 20 km Mini-Sosie? seismic profile details the Quaternary sedimentation history and reveals the structure of the active strike-slip and thrust fault systems that form the western and eastern edges of the Wairarapa basin, respectively. This basin is considered to sit astride the boundary between a zone of distributed strike-slip faults and an active accretionary prism. In the Nelson area, northwestern South Island, previously unrecognised low-angle thrust faults of Neogene or Quaternary age are seen from Mini-Sosie data to occur at very shallow depths. Crustal shortening here was previously thought to arise from movement on high-angle reverse faults, and the identification of these low-angle faults has prompted a reassessment of that model. A grid of 18 km of Mini-Sosie seismic data from the central eastern South Island delineates Neogene or Quaternary thrust faults in Cenozoic sediments. The thrusts are interpreted as reactivated Early Eocene normal faults, and the thrust fault geometry is dominated by these older structures.

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Relations possibles entre la microseismicité récente et l'astroblème de Charlevoix

Canadian Journal of Earth Sciences ◽

10.1139/e83-151 ◽

1983 ◽

Vol 20 (10) ◽

pp. 1613-1618 ◽

Cited By ~ 4

Author(s):

Denis W. Roy ◽

Reynald DuBerger

Keyword(s):

Shock Wave ◽

North America ◽

Seismic Activity ◽

Ground Surface ◽

Vertical Axis ◽

Normal Faults ◽

Eastern North America ◽

Direct Effects ◽

Mantle Boundary ◽

Crustal Stresses

The limit of the direct effects of the Charlevoix astrobleme in the upper part of the Earth's crust outlines approximately a revolution paraboloid about a vertical axis. It reaches 14 km in depth below the center of the astrobleme and exhibits a 27 km radius at the present-day ground surface. The microearthquakes, which reflect the regional crustal stresses in eastern North America, occur on the normal faults characteristic of the St. Lawrence Lowland tectonic terrain mainly near the astrobleme paraboloid or near a second paraboloid located 7.9 km outside the first one. This second one could result from some yet undefined interference between the crust–mantle boundary and the shock wave responsible for the formation of the astrobleme 350 Ma ago. The very low seismic activity in the vicinity of Petite-Rivière–Saint-François may imply that energy is now building up in that area.

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