Late Holocene Paleo-Uplift Events at the Tapion Restraining Bend in Haiti: Implications for Earthquake Recurrence in the Vicinity of the 2010 Rupture Zone
Abstract
The January 12, 2010, Mw 7.0 earthquake in Haiti was caused by slip on one or more blind thrust faults north of the plate-bounding, left-lateral, strike-slip Enriquillo-Plaintain Garden fault zone (EPGFZ). Thrusting lifted ~50 km of coastline with maximum coastal uplift of 0.64 m. Prior to the 2010 event, the EPGFZ likely ruptured during the 1751 or 1770 earthquakes with left-lateral surface offsets on the main trace of the fault that range from 1.3 to 3.3 m. We mapped and dated evidence of paleo-uplifts near the topographically prominent Tapion restraining bend, an apparent right-step along the main trace of the EPGFZ. We found fossil corals that provide evidence of uplift prior to 2010 at two sites located 6.4 km apart along the steep seaward side of Tapion Ridge, but no other evidence of paleo-uplift anywhere in the 2010 uplift zone. Near the east end of Tapion, growth-position coral at ~ 1m ALC (above living coral post-2010 uplift) gave a 230Th/234U age of 2138 ± 11 yr. 2010 uplift here was ~0.37 m, so that the net uplift from 2138 ± 11 yr until the 2010 earthquake was ~0.63 m. Near the western end of Tapion, emerged in situ coral heads giving ages of 4241 ± 13 and 4346 ± 14 yr are planed off at ~0.5 m ALC and capped by a pebble conglomerate, but we estimate that these corals had extended to ~1 m ALC prior to erosion. An emerged bioerosion notch centered at 0.46 m ALC and the planed tops of the coral heads at ~0.5 m correspond well to the 0.44 m ALC of coral that lived prior to the 2010 uplift at this site. A higher emerged bioerosion notch centered at ~0.93 m ALC corresponds well to the elevation of the nearby 4241 ± 13 and 4346 ± 14 yr corals at ~1.0 m ALC prior to being planed off to ~0.5 m. The dated corals and 0.93 m ALC notch indicate ~0.5 m net uplift from ~4241 ± 13 until the 2010 earthquake. Thus, fossil corals at two sites near Tapion are now at similar elevations, but their ages are significantly different and indicate two distinct uplift ages. We interpret these data to suggest that significant variability in uplift occurred in past thrust events, similar to the variability documented for the 2010 earthquake. The distinct bioerosion notches at one of the two sites indicate that sea level was relatively stationary for hundreds of years at least twice and that uplift events in the Tapion restraining bend have recurrence intervals on the order of 2000 years. We propose that this episodic uplift history may reflect events on buried thrust faults associated with the Tapion restraining bend. Small offsets on the main trace of the EPGFZ east of the proposed Tapion restraining bend indicate surface ruptures on the main trace of the EPGFZ at intervals of 200-300 yrs. Our data suggest that the longer term recurrence of blind thrust events in the bend area may be an order of magnitude less frequent than the recurrence of strike-slip events on the main EPGFZ.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T33G2491T
- Keywords:
-
- 7221 SEISMOLOGY / Paleoseismology;
- 7230 SEISMOLOGY / Seismicity and tectonics;
- 8150 TECTONOPHYSICS / Plate boundary: general;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution