Model implications

The model above implies that the rupture occured offshore, with its downdip end located directly below the coastline. It predicts up to 10 cm of vertical coseismic uplift at the coast, in particular in the Puerto Plata area.

This model predicts no significant coseismic deformation (at the precision level of our GPS measurements, i.e. 5 mm horizontally and 8 mm vertically) beyond sites MONC and LAVE. This is consistent with the absence of significant coseismic displacement measured at sites CAPT, SROD, MONC, LVEG, and CASX. It also suggests that the offset measured at sites TERR, ARRO, and LAVE and not of coseismic origin. They may result from lower data quality (at ARRO, for instance, Table 4.3) or from equipment calibration errors during any of the 1999, 2001, or 2003 surveys.

Figure 7.2: Geologic interpretation of the preferred coseismic model in a cross-section perpendicular to the coast in the area of Puerto Plata.

Figure 7.2 shows a geologic interpretation of the coseismic model presented above. Assuming that the North Hispaniola Fault dips 15$^o$ to the southwest, as the preferred coseismic rupture plane, its surface trace (33 km offshore) and the depth of the preferred coseismic rupture plane imply that the rupture occurred above the North Hispaniola Fault. Note that there is a thrust at the seafloor south of the North Hispaniola Fault zone that could be the updip extension of the earthquake rupture (Figure 7.3). This trust could be an ``out of sequence'' fault that has propagated off the lower North Hispaniola fault. Alternatively, the dip angle of the North Hispaniola Fault maybe less than 15$^o$i (at least for some segments), in which case it may coincide with the rupture modeled here.

Figure 7.3: Figures from Dolan et al., 1998. Top: map of active faults on northern margin of Hispaniola in the Puerto Plata area. The main Sept. 2003 event is shown as the large red circle, smaller red circles are aftershocks (locations from NEIC catalog) Note the location of the 1953 Sosua earthquake (blue circle), just west of the 2003 Puerto Plata event; Bottom: seismic reflection profile, starting offshore Sosua and continuing to the NNW. Note the series of 3 anticlinal folds on the margin slope. The southernmost one could be the surface expression of the fault that ruptured during the Sept. 2003 event.