Slip rate and earthquake recurrence along the central Septentrional fault, North American–Caribbean plate boundary, Dominican Republic

Abstract

[1] The Septentrional fault zone (SFZ) is the major North American-Caribbean, strikeslip, plate boundary fault at the longitude of eastern Hispaniola. The SFZ traverses the densely populated Cibao Valley of the Dominican Republic, forming a prominent scarp in alluvium. Our studies at four sites along the central SFZ are aimed at quantifying the late Quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern Caribbean. Our investigations of excavations at sites near Rio Cenovi show that the most recent ground-rupturing earthquake along this fault in the north central Dominican Republic occurred between A.D. 1040 and A.D. 1230, and involved a minimum of $4 m of left-lateral slip and 2.3 m of normal dip slip at that site. Our studies of offset stream terraces at two locations, Rio Juan Lopez and Rio Licey, provide late Holocene slip rate estimates of 6-9 mm/yr and a maximum of 11-12 mm/yr, respectively, across the Septentrional fault. Combining these results gives a best estimate of 6-12 mm/yr for the slip rate across the SFZ. Three excavations, two near Tenares and one at the Rio Licey site, yielded evidence for the occurrence of earlier prehistoric earthquakes. Dates of strata associated with the penultimate event suggest that it occurred post-A.D. 30, giving a recurrence interval of 800-1200 years. These studies indicate that the SFZ has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake.INDEX TERMS: 7221 Seismology: Paleoseismology;

Oblique collision in the northeastern Caribbean from GPS measurements and geological observations

“…In northern Hispaniola, the right stepping, left‐lateral Septentrional fault is responsible for the uplift of the Cordillera Septentrional in its area of maximum fault curvature in the northern Dominican Republic and for active folding and faulting at its contact with late Neogene to Holocene units of the Cibao valley [ Calais et al , 1992; Mann et al , 1998]. Fault trenching studies by Prentice et al [1993], Mann et al [1998], and Prentice et al [2002] along the Septentrional fault in northern Dominican Republic show that the most recent ground‐rupturing earthquake occurred over 800 years ago and involved a minimum of 4 m of left‐lateral slip. In addition, offset stream terrace risers along the Septentrional fault provide Holocene left‐lateral slip rate estimates of 9 ± 3 mm/yr [ Prentice et al , 2002].…”

“…Fault trenching studies by Prentice et al [1993], Mann et al [1998], and Prentice et al [2002] along the Septentrional fault in northern Dominican Republic show that the most recent ground‐rupturing earthquake occurred over 800 years ago and involved a minimum of 4 m of left‐lateral slip. In addition, offset stream terrace risers along the Septentrional fault provide Holocene left‐lateral slip rate estimates of 9 ± 3 mm/yr [ Prentice et al , 2002]. Marine geophysical surveys north of Hispaniola [ Dillon et al , 1992; Dolan et al , 1998] and Puerto Rico [ Masson and Scanlon , 1991; Grindlay et al , 1997] indicate that the Septentrional fault zone extends eastward as far as the Mona rift with earthquake evidence for strike‐slip motion [ McCann and Sykes , 1984; Calais et al , 1992] (Figure 4a).…”

“…A third and final set of questions relates to the seismic hazard of this particularly wide, seismogenic, and densely populated segment of the North America‐Caribbean plate boundary where geologic fault slip studies have only been conducted on only one segment of the Septentrional fault [ Prentice et al , 1993; Mann et al , 1998; Prentice et al , 2002] (Figure 2a) and where numerous, large historical earthquakes felt over the past 500 years may have originated on the inner set of strike‐slip faults (Septentrional, Enriquillo) or on the outer set of low‐angle thrust faults (North Hispaniola‐Puerto Rico). These historical events are potentially large and destructive as shown by the M7.2–8.1 1943–1953 earthquake series that occurred along the low‐angle North Hispaniola fault between northeastern Hispaniola and the Bahama Platform [ Dolan and Wald , 1998] (Figure 2a).…”

Contrasting origins of serpentinites in a subduction complex, northern Dominican Republic

“…The strike-slip displacements in the northern Dominican Republic are greater than 60 km along the Camú fault zone (Pindell and Draper, 1991;Draper and Nagle, 1991) and over 200 km along the Septentrional fault zone (Mann et al, 1984;Draper and Nagle, 1991). The movement along strike of the Septentrional fault zone is estimated to be 6-12 mm/a (Prentice et al, 2003). There is seismic activity along the extension of these faults beneath the seafl oor, but there is no signifi cant seismic activity along these faults on land (http://neic.usgs.gov/neis/ epic).…”

Late Holocene strike-slip offset of a subsurface channel interpreted from three-dimensional seismic data, eastern offshore Trinidad

“…For shallowly buried, active, onland strike-slip faults, extensive and carefully sited fault trenching is required to excavate offset channel features on both fault blocks. Dateable material from both halves of the offset channel can then be used to determine long-term slip rates (Prentice et al, 2003). Determining offsets on submarine strike-slip faults poses a special problem; seafl oor excavation and direct observation of the seafl oor fault trace and its offset features are impossible to conduct at the same level of detail and direct sampling as routinely done for subaerially exposed strike-slip faults.…”