Soil-column depth-dependent seismic site coefficients and hazard maps for the Upper Mississippi Embayment

The presence of deep unconsolidated deposits in the Upper Mississippi Embayment (UME) has an important impact on surface motions and has been the subject of several studies including a study by two of us, who integrated probabilistic seismic hazard analysis (PSHA) with nonlinear site effects (NL). This study extends the PSHA-NL procedure to (1) incorporate a finite-fault model capable of generating near-source motions instead of using point-source models only, (2) better approximate the range of available attenuation relations for the Central and Eastern United States (CEUS), (3) examine the hazard at very high levels of shaking, and (4) propagate generated rock motions through randomized soil profile properties to achieve a more consistent probabilistic procedure. The extended PSHA-NL procedure is used to develop updated depth-dependent site coefficients for the UME, which generally provides a lower hazard at short periods but a higher hazard at longer periods than current approaches. Proposed probabilistic seismic hazard maps, at selected spectral accelerations, that incorporate the proposed site effects are also presented for the UME and are systematically compared with seismic hazard maps proposed by others.