Comment on “Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region” by U. ten Brink et al.

Abstract

[1] The analysis of historical earthquakes in the northeastern Caribbean by ten Brink et al. [2011, hereafter TB11] addresses the occurrence of large and destructive historical earthquakes associated with the North American-Caribbean plate boundary. One conclusion presented in TB11 is that the recurrence interval for large earthquakes on the left-lateral, strike-slip Septentrional Fault (SF) (Figure 1a) is approximately 300 years. Their Figure 7 shows rupture of the SF across the entire island of Hispaniola in CE 1200, 1542, and 1842. Our comment challenges this model for SF earthquake recurrence because it is inconsistent with our published paleoseismic data that show no large historical earthquake is associated with surface rupture along the SF east of Santiago (Figure 1a) [Prentice et al., 1993;Mann et al., 1998; Prentice et al., 2003]. [2] Historical records of earthquakes prior to the twentieth century rarely provide direct observations linking a specific fault with a particular earthquake. Researchers of historical earthquakes typically formulate hypotheses such as those presented in TB11 associating earthquakes with particular faults, based on their modeled isoseismals. In contrast, paleoseismic studies based on direct observations of the fault zone and reliable age analyses provide fault-specific data to constrain when, within the uncertainty of the data, a particular section of a fault did or did not produce large surface-rupturing earthquakes. A model based solely on historical accounts of ground shaking and damage is useful in the absence of paleoseismic data, but interpretations based on historical accounts alone do not have the same resolution as geologic data that constrain the timing and location of fault surface rupture. The ambiguity inherent in using intensity centers alone to assign a historical earthquake to a particular fault is well illustrated by Figure 3 in Bakun et al., [2012], which shows the intensity center for the 1946 earthquake immediately adjacent to the SF (Figure 1a, green triangle). Yet this earthquake is well known to have occurred on the North Hispaniola thrust belt, not on the SF [Dolan and Wald, 1998]. (We note an error in TB11’s Figure 4 showing the intensity center for the 1946 earthquake: the intensity center and all intensity locations are systematically mislocated about 50 km to the north compared to Figure 3 in Bakun et al., [2012].) TB11 dismiss existing paleoseismic data as a constraint when they attribute the 1842 and 1562 Hispaniola earthquakes to the SF. Our published paleoseismic data contradict their interpretation; therefore, we believe their model for SF recurrence is incorrect.