REFINEMENT OF THRUST FAULTING MODELS FOR THE CENTRAL NEW MADRID SEISMIC ZONE

We present the results of the joint relocation of events recorded duri ng 1989-1992 by the PANDA network in the central New Madrid seismic zo ne. The near-surface material in the study area is a gently-dipping la yer of poorly consolidated sediments with low P-wave velocity and high V-p/V-s (estimated values: 1.8 km s(-1) and 3). The sediments are und erlain by high-velocity Paleozoic rocks. Under the network the differe nce in sediment thickness is only 0.6 km, but because of the low veloc ities the location of the events using layered models is affected by e rrors. Application of the joint hypocentral determination (JHD) techni que to a subset of 580 events shows that the single-event locations ma y be in error by as much as 1 km in depth, depending on where the even ts are located. Analysis of synthetic data generated for a realistic 3 -D velocity model supports the JHD results. The analysis of synthetic data also suggests that a V-p/V-s less than or equal to 2.3 is more ap propriate for the post-Paleozoic Mississippi embayment sediments. Base d on the JHD locations we present a new interpretation of the seismici ty, with two en-echelon SW-dipping thrust faults connected by a west-d ipping thrust fault. These faults appear associated with the Reelfoot scarp and its northern extension, the Kentucky bend scarp. (C) 1997 El sevier Science B.V.