Fault slip rates in the modern new Madrid seismic zone

Science

Volumn 286, Issue 5442, 1999, Pages 1135-1138

  Mueller, Karl ^a   Champion, Jocasta ^a   Guccione, Margaret ^b   Kelson, Keith ^c  

^a UNIVERSITY OF COLORADO   (United States)

^b UNIVERSITY OF ARKANSAS   (United States)

^c William Lettis and Associates   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EARTHQUAKE; FAULT SLIP; SEISMICITY;

ARTICLE; EARTHQUAKE; GEOLOGY; PRIORITY JOURNAL; SEDIMENT;

UNITED STATES;

EID: 0033527723     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.286.5442.1135     Document Type: Article

References (22)

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11. The digital elevation model (DEM) was created from a digitized 1939 U.S. Army Corps of Engineers 1:62,500 scale topographic map with a 5′ contour interval. The resulting DEM was manipulated in ENVI to produce the shaded relief map seen in Fig. 1B.
12. A. Newman et al., Science 284, 619 (1999).
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14. R. T. Saucier, Geomorphotogy and Quaternary Geologic History of the Lower Mississippi Valley, prepared for the President, Mississippi River Commission (U.S. Army Waterways Experiment Station, Vicksburg, MS, 1994), vol. 2.
15. We depth-corrected profile LDC-2 of (9) by tying prominent reflectors with high impedance contrast (for example, base Quaternary, top Porters Creek Clay, and top Cretaceous) to a nearby welt, the Kate Wright No. 1, located less than 100 m from the western endpoint of the seismic line. Short straight segments of reflectors were traced from the depth-migrated section; these segments were then depth-corrected with the known depth of correlative stratigraphic units in the nearby well.
16. We measured limb width in the three trench excavations by projecting the steepest portion of the east-facing fold limbs to their intersections with projections of adjacent flat-lying or gently west-dipping strata (Fig. 4C). We ignored large collapse features and sandblows in these projections.
17. J. Purser and R. Van Arsdale, Bull. Seismol. Soc. Am. 88, 1204 (1998).
18. J. Shaw and J. Suppe, Geol. Soc. Am. Bull. 106, 607 (1994).
19. For transferal of fault slip across multibend fault-bend folds, we argue that the minimum total change in fault trajectory (that is, the change in fault dip measured across all bends) is defined by the sum of the steepest portions of individual kink bands. This is for the case in which the amount of fault slip exceeds the spacing between adjacent active axial surfaces. We do not suggest that fault-bend folds are perfectly angular and completely reflect changes in fault trajectory (for example, fault bends). Increase in the radii of curvature of fault-bend folds as they propagate upward through sedimentary rocks depends on both the rigidity of folded sedimentary beds and the spacing of flexural slip faults that accommodate kink-band migration. We argue that our assumption of fault-related folding is a valid deformation mechanism for the Reelfoot scarp because the bend in the thrust occurs at a shallow depth (that is, 500 m) and because overlying Tertiary sediments are well bedded. We modeled the fault-bend fold as made up of two bends where it is imaged by the seismic reflection profile and boring profile and three bends where the trench excavations were completed. These bends are apparent at the surface as smaller scarps in the larger Reelfoot "scarp" but are not resolvable on the shaded relief image shown in Fig. 1B.
20. For the slip rate defined by the limb widths measured in the trenches, uncertainty is calculated as standard error, which takes into account both the variance in the measurements and the uncertainty in the radiocarbon age (for example, 0.7 mm/year). For the slip rate defined by structural relief and fault dip, uncertainty depends only on the uncertainty in the radiocarbon age because only one measurement, 9.1 m of uplift, is used (for example, 0.2 mm/year). Our attempt to fit the dip of the 55° fault ramp to the seismicity data and the location of the Reelfoot scarp can be varied by as much as 5° of dip. For a fault dip of 50°, we determined a slip rate of 5.2 mm/year; for a fault dip of 60°, we determined a rate of 4.6 mm/year.
21. We used a slip vector on the blind thrust fault of 55°, N88°W, perpendicular to the strike of the Reelfoot scarp at the trench site. The rate of horizontal shortening perpendicular to the strike of the Reelfoot thrust is equivalent to the cosine of the dip of the thrust (that is, 55°) multiplied by the slip rate. For the two slip rates we determined, this yields rates of 2.8 or 3.4 mm/year. The cosine of the horizontal angle between the trend of the slip vector on the thrust and the strike of the Cottonwood Grove fault (that is, 50°) is then multiplied by the rate of horizontal shortening across the thrust to yield the slip rate on the regional strike-slip system of 1.8 or 2.2 mm/year
22. E. S. Schweig and M. A. Ellis, Science 264, 1308 (1994).