How Old is the New Madrid Seismic Zone?

1994 ◽  
Vol 65 (2) ◽  
pp. 172-179 ◽  
Author(s):  
Thomas L. Pratt
Keyword(s):  
Fault Zone ◽  
Fault Model ◽  
New Madrid Seismic Zone ◽  
Reverse Fault ◽  
Seismic Zone ◽  
Lake County ◽  
Recurrence Times ◽  
Analysis Techniques ◽  
Large Earthquakes ◽  
New Madrid

Abstract Current seismicity levels on the New Madrid seismic zone should produce about 0.11 cm/year of horizontal slip which, when compared with uplift of 42 m in the subsurface strata below the Lake County uplift and assuming a 31° reverse fault model, indicates that the present seismicity levels could not have been present for more than about 64,000 years. If seismicity in the region has persisted for a much longer period of time, then (1) the seismicity has moved spatially between several deformed zones (Crowley’s Ridge and the Crittenden County fault zone); (2) the seismicity is episodic in nature, and active periods similar to the present occur between long quiescent times; or (3) there have been far fewer large earthquakes than predicted by extrapolation of the Gutenberg-Richter relation to higher magnitudes. Any of these scenarios indicates that assessing the hazard from large earthquakes is more complicated than conventional analyses have assumed because either the seismicity locations or rates change or analysis techniques relying on the Gutenberg-Richter relation are invalid for estimating the recurrence times of large earthquakes in the New Madrid area.

Faulting along the southern margin of Reelfoot Lake, Tennessee

1998 ◽  
Vol 88 (1) ◽  
pp. 131-139 ◽  
Author(s):  
Roy Van Arsdale ◽  
Jodi Purser ◽  
William Stephenson ◽  
Jack Odum
Keyword(s):  
Fault Zone ◽  
Lake Basin ◽  
New Madrid Seismic Zone ◽  
Reverse Fault ◽  
Seismic Reflection Profile ◽  
Seismic Zone ◽  
Seismic Line ◽  
Southern Margin ◽  
Main Shocks ◽  
New Madrid

Abstract The Reelfoot Lake basin, Tennessee, is structurally complex and of great interest seismologically because it is located at the junction of two seismicity trends of the New Madrid seismic zone. To better understand the structure at this location, a 7.5-km-long seismic reflection profile was acquired on roads along the southern margin of Reelfoot Lake. The seismic line reveals a westerly dipping basin bounded on the west by the Reelfoot reverse fault zone, the Ridgely right-lateral transpressive fault zone on the east, and the Cottonwood Grove right-lateral strike-slip fault in the middle of the basin. The displacement history of the Reelfoot fault zone appears to be the same as the Ridgely fault zone, thus suggesting that movement on these fault zones has been synchronous, perhaps since the Cretaceous. Since the Reelfoot and Ridgely fault systems are believed responsible for two of the main-shocks of 1811-1812, the fault history revealed in the Reelfoot Lake profile suggests that multiple mainshocks may be typical of the New Madrid seismic zone. The Ridgely fault zone consists of two northeast-striking faults that lie at the base of and within the Mississippi Valley bluff line. This fault zone has 15 m of post-Eocene, up-to-the-east displacement and appears to locally control the eastern limit of Mississippi River migration. The Cottonwood Grove fault zone passes through the center of the seismic line and has approximately 5 m of up-to-the-east displacement. Correlation of the Cottonwood Grove fault with a possible fault scarp on the floor of Reelfoot Lake and the New Markham fault north of the lake suggests the Cottonwood Grove fault may change to a northerly strike at Reelfoot Lake, thereby linking the northeast-trending zones of seismicity in the New Madrid seismic zone.

Structure of the Lake County uplift: New Madrid seismic zone

1998 ◽  
Vol 88 (5) ◽  
pp. 1204-1211
Author(s):  
Jodi L. Purser ◽  
Roy B. Van Arsdale
Keyword(s):  
Hanging Wall ◽  
New Madrid Seismic Zone ◽  
Reverse Fault ◽  
Seismic Zone ◽  
Lake County ◽  
Western Margin ◽  
Kink Bands ◽  
Brittle Ductile Transition ◽  
Step Over ◽  
New Madrid

Abstract The central segment of the New Madrid seismic zone lies within a left step-over zone between two northeast-striking, right-lateral, strike-slip fault systems. Within this compressional step-over zone is the topographically and structurally high Lake County uplift, which includes the Tiptonville dome and Ridgely ridge. We believe these structures are a consequence of deformation in the hanging wall above the northwest-striking, southwest-dipping Reelfoot reverse fault. Reelfoot fault dips 73° from the surface to the top of the Precambrian at a depth of approximately 4 km. From 4 to 12 km depth, the fault dips 32° and is seismically active. Based on a fault-bend fold model, we believe that the Reelfoot fault becomes horizontal and aseismic at the top of the quartz brittle-ductile transition zone, at approximately 12 km depth. Our data indicate that the western margin of the Tiptonville dome-Ridgely ridge and the western margin of the Lake County uplift are bounded by east-dipping kink bands (backthrusts). Recent work suggests that the Reelfoot fault is responsible for the 7 February 1812, M 8 New Madrid earthquake. However, the Reelfoot fault has a surface area that is less than that necessary for an M 8 earthquake. A possible solution to this discrepancy between magnitude and fault plane area is that the associated backthrusts are seismogenic.

Evidence for recurrent faulting in the New Madrid seismic zone from Mini‐Sosie high‐resolution reflection data

Geophysics ◽  
1986 ◽  
Vol 51 (9) ◽  
pp. 1760-1788 ◽  
Author(s):  
John L. Sexton ◽  
Paul B. Jones
Keyword(s):  
High Resolution ◽  
Close Association ◽  
Late Eocene ◽  
Small Displacement ◽  
New Madrid Seismic Zone ◽  
Data Sets ◽  
Reverse Fault ◽  
Seismic Zone ◽  
Reflection Data ◽  
New Madrid

A Mini‐Sosie™ high‐resolution seismic reflection survey was conducted on Reelfoot scarp in the northwestern Tennessee portion of the New Madrid seismic zone. Interpretation of the Mini‐Sosie data revealed the need to reinterpret previously collected reflection data obtained from explosive source and Vibroseis® surveys. Interpretation and integration of the three data sets have resulted in a new model for the subsurface of Reelfoot scarp and provide evidence for recurrent movement along Reelfoot fault, the major reverse fault associated with Reelfoot scarp. Estimated displacements on Reelfoot fault vary from 60 m (60 ms) for late Paleozoic rocks to 15 m (20 ms) for late Eocene sedimentary units. No clear offsets are observed on this particular fault for units younger than late Eocene age; however, uplift, folding, and related structures are observed in younger sediments. An observed variation of offset with depth (age) and the presence of the younger structures are evidence of reactivation of Reelfoot fault. Small‐offset (10 to 20 m) faults were also detected and have been interpreted to have constant displacement with depth, and therefore, to have occurred as a single faulting event rather than as recurrent movement on a fault plane. Two of these faults are interpreted to have been formed in the middle to late Eocene. A small reverse fault located a few hundred feet east of Reelfoot fault appears to be a single faulting event which extends into sediments of Holocene age. There is a small displacement graben structure which probably extends into Holocene age sediments near the apex of the folded sediments of Reelfoot scarp. The location of the graben structure coincides with a zone of small‐offset nomal faulting with 2 to 3 m of total offset within Holocene sediments observed in a trench excavated over Reelfoot scarp. This small zone of faulting has previously been interpreted to be of tectonic origin. The close association of the faults observed in the trench and the graben structure observed on the seismic data suggests that the two features are directly related, and that both structures were formed by Holocene‐era reactivation of Reelfoot fault. Additional evidence supporting our interpretation is provided by synthetic seismograms for models derived from the various data sets and paleosections of the high‐resolution reflection data. A fault map based on all the reflection data shows that our interpretation is consistent with the data sets.

Tectonic Deformation in the New Madrid Seismic Zone: Inferences from Boundary Element Modeling

1992 ◽  
Vol 63 (3) ◽  
pp. 407-425 ◽  
Author(s):  
J. S. Gomberg
Keyword(s):  
Boundary Element ◽  
Strain Field ◽  
Tectonic Deformation ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
Lake County ◽  
Element Modeling ◽  
Dimensional Boundary ◽  
Length Width ◽  
New Madrid

Abstract The lack of instrumental recordings and of obvious fault scarps associated with the 1811–1812 New Madrid earthquakes necessitates examination of more subtle indicators of the geometry and type of faulting responsible for these events. Morphologic and geologic features and the distribution of modern seismicity are used to infer the number, strike, length, width, type of faulting (strike- or dip-slip), and spatial variability of slip for the major faults in the New Madrid Seismic Zone (NMSZ). This is accomplished through two-dimensional boundary-element modeling of the strain field arising from slip on hypothetical faults that is driven by either coseismic or uniform regional strains. Tectonic deformation is reflected in the seismicity and in morphologic and geologic features including (1) the Lake County uplift, (2) Reelfoot Lake, (3) the deformed rocks of the Blytheville arch, and (4) the St. Francis Sunk Lands. Many of these features can be qualitatively explained as resulting from tectonic deformation due to slip on two left-stepping right-lateral strike-slip faults that are coincident with the northeast-trending zones of seismicity and the Blytheville arch. The morphology appears to be, at least in part, a consequence of major earthquakes that rupture these faults. The locations of the 1811–1812 and largest post-1812 earthquakes and the models are consistent with a process in which the 1811–1812 earthquakes relieved accumulated regional shear strain causing the greatest post-1812 shear strains to exist at the ends of the fault zone. Modeling results also suggest that the numerous small earthquakes in the NMSZ are not aftershocks of the 1811–1812 earthquakes but instead represent continuous localized adjustments to a uniform regional strain field. The Bootheel lineament does not appear to be significant in the shaping the morphology, geologic structure, and pattern of seismicity of the NMSZ. The inferred length of the 1811–1812 earthquake ruptures suggest that their sizes may have been overestimated. Model predicted subsidence within the St. Francis Sunk Lands suggests that tectonic deformation may also influence alluvial processes in the NMSZ.

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