Enriquillo-Plantain Garden Fault Zone Research Articles

The 2021 Mw 7.2 Haiti earthquake: Blind thrust rupture revealed by space geodetic observations and Bayesian estimation

On 14 August 2021, a large earthquake struck the southern region of Haiti. The epicenter of this earthquake is located relatively close to the Enriquillo–Plantain Garden Fault (EPGF) zone, a major active fault with a strike-slip mechanism in the southern part of Hispaniola. Since the epicenter of this earthquake is located relatively close to the Enriquillo–Plantain Garden Fault zone, one might think that the EPGF is the causative fault. Using a Bayesian approach, the Sentinel-1 data is then utilized to investigate the seismogenic fault responsible for the 2021 Haiti earthquake. The Bayesian inversion indicated that the mainshock ruptured a north-dipping fault with a strike and a dip of 270.9° and 69.2°, respectively, and buried at a depth of 10.3 km from the earth’s surface. The preferred slip model showed that the rupture did not reach the surface and was confined at a depth of ∼6 km to ∼32 km. The preferred fault geometry is in good agreement with the relocated aftershock distribution and is inconsistent with the EPGF system configuration. It indicates that the EPGF is probably not the seismogenic fault responsible for the 2021 Haiti earthquake. Instead, results suggested that the 2021 Haiti earthquake ruptured an unmapped blind fault.

Surface Deformation Surrounding the 2021 Mw 7.2 Haiti Earthquake Illuminated by InSAR Observations

ABSTRACT Earthquakes pose a major threat to the people of Haiti, as tragically shown by the catastrophic 2010 Mw 7.0 earthquake and more recently by the 2021 Mw 7.2 earthquake. Both events occurred within the transpressional Enriquillo–Plantain Garden fault zone (EPGFZ), which runs through the southern peninsula of Haiti and is a major source of seismic hazard for the region. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) data are used to illuminate the ground deformation patterns associated with the 2021 event. The analysis of Sentinel-1 and Advanced Land Observation Satellite (ALOS)-2 InSAR data shows (1) the broad coseismic deformation field; (2) detailed secondary fault structures as far as 12 km from the main Enriquillo–Plantain Garden fault (EPGF), which are active during and after the earthquake; and (3) postseismic shallow slip, which migrates along an ∼40 km unruptured section of the EPGF for approximately two weeks following the earthquake. The involvement of secondary faults in this rupture requires adjustments to the representation of hazard that assumes a simple segmented strike-slip EPGF. This work presents the first successful use of phase gradient techniques to map postseismic deformation in a vegetated region, which opens the door to future studies of a larger number of events in a wider variety of climates.

Rupture Segmentation of the 14 August 2021 Mw 7.2 Nippes, Haiti, Earthquake Using Aftershock Relocation from a Local Seismic Deployment

ABSTRACT The 14 August 2021 Mw 7.2 Haiti earthquake struck 11 yr after the devastating 2010 event within the Enriquillo Plantain Garden (EPG) fault zone in the Southern peninsula of Haiti. Space geodetic results show that the rupture is composed of both left-lateral strike-slip and thrust motion, similar to the 2010 rupture; but aftershock locations from a local short-period network are too diffuse to precisely delineate the segments that participated in this rupture. A few days after the mainshocks, we installed 12 broadband stations in the epicentral area. Here, we use data from those stations in combination with four local Raspberry Shakes stations that were already in place as part of a citizen seismology experiment to precisely relocate 2528 aftershocks from August to December 2021, and derive 1D P- and S-crustal velocity models for this region. We show that the aftershocks delineate three north-dipping structures with different strikes, located to the north of the EPG fault. In addition, two smaller aftershock clusters occurred on the EPG fault near the hypocenter area, indicative of triggered seismicity. Focal mechanisms are in agreement with coseismic slip inversion from Interferometric Synthetic Aperture Radar data with nodal planes that are consistent with the transpressional structures illustrated by the aftershock zones.

The 8 April 1860 Jour de Pâques Earthquake Sequence in Southern Haiti

ABSTRACT The grave threat posed by the Enriquillo-Plantain Garden fault zone (EPGFZ) and other fault systems on the Tiburon Peninsula in southern Haiti was highlighted by the catastrophic M 7.0 Léogâne earthquake on 12 January 2010 and again by the deadly M 7.2 Nippes earthquakes on 14 August 2021. Early Interferometric Synthetic Aperture Radar observations suggest the 2021 earthquake broke structures associated with this fault system farther west of the 2010 event, but the rupture zones of both events are separated by a ∼50 km gap. This sequence provided the impetus to reconsider a nineteenth century earthquake that may have occurred within this gap. Though previous studies identified a single moderately large event on 8 April 1860, original sources describe a complex and distributed seismic sequence to the west of Port-au-Prince. These provide evidence for an initial event to the west of Les Cayes, on the southern coast of the Tiburon Peninsula. This was followed on the morning of 8 April 1860 by a damaging earthquake near l’Anse-à-Veau along the northern coast of the peninsula, which was succeeded 14 hr later by a larger mainshock to the east. Although locations cannot be determined precisely from extant macroseismic data, our preferred scenario includes an intensity magnitude (MI)∼6.2 foreshock, followed by an MI∼6.8 mainshock wholly or partially on the EPGFZ to the east of the foreshock. Our results suggest that, although earthquakes tend to trigger subsequent earthquakes on immediately neighboring fault segments, sequences can include gaps due to strain release by poorly characterized earthquakes in the historic past. We also document 83 aftershocks to the 1860 earthquake sequence, including a previously unknown damaging shock, estimated MI∼6.6, on 10 April 1860 near Jérémie, farther west of l’Anse-à-Veau.

From neogene thin-skin to recent thick-skin deformation in Haiti fold-and-thrust belt (Western Hispaniola)

Haiti lies along the North Caribbean plate boundary, marked by two major left-lateral strike-slip faults. A southwest-verging Trans-Haitian fold-and-thrust belt (FTB), mostly affecting tertiary carbonate platform, developed in central Haiti between the two faults, south of the Massif du Nord and the San Juan–Los Pozos Fault Zone, as a result of north-south shortening. The large NW-SE antiformal Gonâve Island and Ridge mark the southwest termination of the FTB as it encountered the Southern Peninsula and Enriquillo-Plantain Garden Fault Zone. We show that this collision resulted in a tightening of the deformed wedge and thrust faults rooted deeper into the crust, leading to a transition from thin-skinned to thick-skinned tectonics in the Pliocene. These short- (3–6 km) and long- (15–30 km) wavelength folding deformations are temporally distinct in the north and more concomitant in the south, where compressional thin-skinned deformation is still active. The thick-skinned shortening was mostly expressed during the Quaternary, as shown by the formation of folds and uplift of terraces between 1.7 Ma and today. This thick-skinned detachment is characterised by a stronger imprint of strike-slip component, dragging the FTB to a more E-W direction in its northwest and southeast extremities. Understanding of the fault zone geometry of the recent 2010 Haiti earthquake (M = 7.2) could be reconsidered in the light of this tectonic transition.

Haiti-Drill: an amphibious drilling project workshop

Abstract. The Haiti region – bounded by two strike-slip faults expressed both onshore and offshore – offers a unique opportunity for an amphibious drilling project. The east–west (EW)-striking, left lateral strike-slip Oriente–Septentrional fault zone and Enriquillo–Plantain Garden fault zone bounding Haiti have similar slip rates and also define the northern and southern boundaries of the Gonâve Microplate. However, it remains unclear how these fault systems terminate at the eastern boundary of that microplate. From a plate tectonic perspective, the Enriquillo–Plantain Garden fault zone can be expected to act as an inactive fracture zone bounding the Cayman spreading system, but, surprisingly, this fault has been quite active during the last 500 years. Overall, little is understood in terms of past and present seismic and tsunami hazards along the Oriente–Septentrional fault zone and Enriquillo–Plantain Garden fault zone, their relative ages, maturity, lithology, and evolution – not even the origin of fluids escaping through the crust is known. Given these unknowns, the Haiti-Drill workshop was held in May 2019 to further develop an amphibious drilling project in the Haiti region on the basis of preproposals submitted in 2015 and their reviews. The workshop aimed to complete the following four tasks: (1) identify significant research questions; (2) discuss potential drilling scenarios and sites; (3) identify data, analyses, additional experts, and surveys needed; and (4) produce timelines for developing a full proposal. Two key scientific goals have been set, namely to understand the nature of young fault zones and the evolution of transpressional boundaries. Given these goals, drilling targets were then rationalized, creating a focus point for research and/or survey needs prior to drilling. Our most recent efforts are to find collaborators, analyze existing data, and to obtain sources of funding for the survey work that is needed.

Polyphase tectonic history of the Southern Peninsula, Haiti: from folding-and-thrusting to transpressive strike-slip

The Southern Peninsula of Haiti is a seismically active east – west trending transpressive mountain range with elevations over 2 km. Present-day deformation is mainly partitioned along the left-lateral Enriquillo – Plantain Garden Fault Zone (EPGFZ) and associated oblique reverse faults and/or folds. The configuration of these faults, their respective timing, and the role of structural heritage on their development is poorly understood. To address these questions we present the results of extensive field campaigns, combined with satellite imagery interpretation and published data, which allows us to constrain the Cenozoic evolution of the Southern Peninsula. Our results show a polyphase tectonic history consisting of three major tectonic events: 1) Maastrichtian to early Paleocene crustal-scale folding that developed coevally with predominantly north to northeast dipping thrusts, resulting in uplift and erosion of the Cretaceous sedimentary cover in large parts of the Southern Peninsula. 2) Early Miocene uplift and erosion, which was strongest in the southwestern part of the peninsula and decreased eastwards, did not affect the Massif de la Selle. Uplift is most likely unrelated to strike-slip activity but resulted from folding in response to NE – SW shortening that possibly reactivated older, predominantly N- to NE-dipping thrusts. 3) Late Miocene to present-day deformation and uplift. Spatially distributed strike-slip started during the late Miocene and became progressively focused along the EPGFZ in the latest Miocene. Oblique and thrust faults locally post-date strike-slip activity from the Pliocene onward. Increase in compressional deformation from west to east is reflected by a change in structural style, with predominantly strike-slip faults in the west and transpressional faults in the east, the latter possibly rooted on the EPGFZ at depth. Paleo-stresses associated with a strike-slip regime are at a significantly high angle to the trace of the EPGFZ, indicating that the EPGFZ is a mechanically weak fault.

Late Holocene Structural Style and Seismicity of Highly Transpressional Faults in Southern Haiti

AbstractThe devastating 2010 Haiti earthquake (Mw 7.0) was caused by rupture of the Léogâne, blind, thrust fault located 5 km north of the 1,200‐km‐long, left‐lateral, Enriquillo‐Plantain Garden fault zone (EPGFZ). Unexpectedly, the EPGFZ remained largely quiescent or slightly reactivated during the 2010 earthquake. Nevertheless, the EPGFZ still formed a major, crustal boundary between a coseismically uplifted lowland north of the EPGFZ and a subsided area in the highlands south of the fault. Here we use high‐resolution sonar data from two Haitian Lakes that straddle the EPGFZ to demonstrate the presence of a 10‐ to 15‐km‐wide, 120‐km‐long, late Holocene fold‐thrust belt which deforms clastic, lowland basins along the northern edge of the EPGFZ. In the eastern part of the study area, sonar results from Lake Azuey show that the linear trace of the EPGFZ cutting the Holocene lake bed is more deeply buried and less active than the adjacent, newly discovered, northwest striking, northeast dipping Jimani thrust fault that is part of the adjacent, transpressional belt of en echelon thrusts and folds. This structural relationship between a less active EPGFZ and more recently active, transpression‐related Jimani thrust is remarkably similar to the 2010 epicentral area 70 km to the west between the less active EPGFZ and seismogenic, northeast‐dipping, Léogâne thrust during the 2010 Haiti earthquake. In this complex transpressional zone, we propose that coseismic deformation alternates at recurrence intervals of centuries between oblique, transpression‐related structures (Léogâne, Jimani, and Trois Baies thrusts) and the main strike‐slip, plate boundary fault zone (EPGFZ).

How transpressive is the northern Caribbean plate boundary?

Transpressive deformation at the northern Caribbean plate boundary is accommodated mostly by two major strike-slip faults, but the amount and location of accommodation of the compressional component of deformation are still debated. We collected marine geophysical data including multibeam bathymetry and multichannel seismic reflection profiles along this plate boundary around Hispaniola, in the Jamaica Passage, and in the Gulf of Gonâve. The data set allows us to image the offshore active strike-slip faults as well as the compressional structures. We confirm that the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage has a primary strike-slip motion, as indicated by active left-lateral strike-slip-related structures, i.e., restraining bend, asymmetrical basin, en echelon pressures ridges, and horsetail splay. Based on topographic cross sections across the EPGFZ, we image a very limited compressional component, if any, for at least the western part of the Jamaica Passage. Toward the east of the Jamaica Passage, the fault trace becomes more complex, and we identify adjacent compressional structures. In the Gulf of Gonâve, distributed folding and thrust faulting of the most recent sediments indicate active pervasive compressional tectonics. Estimates of shortening in the Jamaica Passage and in the Gulf of Gonâve indicate an increase of the compressional component of deformation toward the east, which nonetheless remains very small compared to that inferred from block modeling based on GPS measurements.

The northern Caribbean plate boundary in the Jamaica Passage: Structure and seismic stratigraphy

Multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage, between Jamaica and Hispaniola. Analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern Caribbean boundary. Stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history. Two distinct crustal domains are interpreted. Typical stratigraphic sequences for the rifted blocks of the Eastern Cayman Trough margin are identified in five basins of the Jamaica Passage, highlighting the eastward limit of the Cayman Trough margin. These inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early Miocene (about 20Ma). A distinct crustal domain that we propose to relate to the Carib Beds (Caribbean typical reflectors A″, B″ and V) is identified in the southern part of the Jamaica Passage, indicating that the Caribbean Large Igneous Province could extend up to the extreme northeast part of the Lower Nicaragua Rise. The left-lateral EPGFZ currently cuts across two pre-existing basins, the Morant and Matley basins. During the activity of the EPGFZ, these basins are deformed and folded indicating a second phase of compression. In contrast, the Navassa basin, located in the middle of the Jamaica Passage, results from the strike-slip motion of the EPGFZ and is interpreted as an asymmetrical basin bordered by the EPGFZ only on its northern side.

Segmentation and kinematics of the North America‐Caribbean plate boundary offshore Hispaniola

AbstractWe explored the submarine portions of the Enriquillo–Plantain Garden Fault zone (EPGFZ) and the Septentrional–Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high‐resolution multibeam echo‐sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate‐boundary structures are a series of strike‐slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50–100 km long cut across pre‐existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike‐slip regime. Along the most recent trace of the SOFZ, we measured a strike‐slip offset of 16.5 km, which indicates steady activity for the past ~1.8 Ma if its current GPS‐derived motion of 9.8 ± 2 mm a−1 has remained stable during the entire Quaternary.

Searching for blind faults: The Haiti subsurface imaging project

On 12 January 2010, Haiti suffered a magnitude 7.0 earthquake near Port-au-Prince, which resulted in a catastrophic loss of life and infrastructure. The effects were particularly severe on the Léogâne fan delta, close to the earthquake's epicenter. Because no unambiguous rupture to the surface has been found, the suspected fault that caused the event has been labeled “blind.” A geophysical team from the University of Houston has undertaken expeditions to Haiti in 2012–2014, with support from the SEG Geoscientists Without Borders program, to try to help build Haiti's geophysical capability and assist in finding subsurface evidence of the proposed blind fault. The team reconnoitered the epicentral region of the 2010 earthquake and selected sites on the Léogâne delta fan for land surveys. The team enjoyed a productive and pleasant interaction with local villagers while receiving access to survey areas and assistance with operations. The resulting 2012 seismic and gravity data provided promise for more detailed surveys that the team undertook in February 2013. Measurements indicated that the soil sediments near Léogâne are Class E — a substantial geohazard. The University of Houston team found a broad and unfaulted anticline in the overlying fan deposit that is consistent with seismogenic movement on a north-dipping reverse fault at greater depth. The axis of the subsurface anticline is in alignment with an east-west-trending zone of localized highway damage and a coral reef that was uplifted during the 2010 earthquake. Lake sonar surveys have given some excellent images of the associated Enriquillo–Plantain Garden fault zone (EPGFZ). As a result of this work, the team plans to bring larger seismic sources to create more detailed and deeper seismic sections (land and lake) and to assist in further development of Haitian geophysical capabilities. The project has provided a remarkable learning experience for staff and students as well as for Haitian colleagues.

Enriquillo-Plantain Garden Fault Zone in Jamaica: Paleoseismology and Seismic Hazard

The countries of Jamaica, Haiti, and the Dominican Republic all straddle the Enriquillo–Plantain Garden fault zone (EPGFZ), a major left‐lateral, strike‐slip fault system bounding the Caribbean and North American plates. Past large earthquakes that destroyed the capital cities of Kingston, Jamaica (1692, 1907), and Port‐au‐Prince, Haiti (1751, 1770), as well as the 2010 Haiti earthquake that killed more than 50,000 people, have heightened awareness of seismic hazards in the northern Caribbean. We present here new geomorphic and paleoseismic information bearing on the location and relative activity of the EPGFZ, which marks the plate boundary in Jamaica. Documentation of a river bank exposure and several trenches indicate that this fault is active and has the potential to cause major destructive earthquakes in Jamaica. The results suggest that the fault has not ruptured the surface in at least 500 yr and possibly as long as 28 ka. The long period of quiescence and subdued geomorphic expression of the EPGFZ indicates that it may only accommodate part of the ∼7–9 mm/yr plate deformation rate measured geodetically and that slip may be partitioned on other undocumented faults. Large uncertainties related to the neotectonic framework of Jamaica remain and more detailed fault characterization studies are necessary to accurately assess seismic hazards.

GPS estimates of microplate motions, northern Caribbean: evidence for a Hispaniola microplate and implications for earthquake hazard

SUMMARY We use elastic block modelling of 126 GPS site velocities from Jamaica, Hispaniola, Puerto Rico and other islands in the northern Caribbean to test for the existence of a Hispaniola microplate and estimate angular velocities for the Gonave, Hispaniola, Puerto Rico-Virgin Islands and two smaller microplates relative to each other and the Caribbean and North America plates. A model in which the Gonave microplate spans the whole plate boundary between the Cayman spreading centre and Mona Passage west of Puerto Rico is rejected at a high confidence level. The data instead require an independently moving Hispaniola microplate between the Mona Passage and a likely diffuse boundary within or offshore from western Hispaniola. Our updated angular velocities predict 6.8 ± 1.0 mm yr−1 of left-lateral slip along the seismically hazardous Enriquillo-Plantain Garden fault zone of southwest Hispaniola, 9.8 ± 2.0 mm yr−1 of slip along the Septentrional fault of northern Hispaniola and ∼14–15 mm yr−1 of left-lateral slip along the Oriente fault south of Cuba. They also predict 5.7 ± 1 mm yr−1 of fault-normal motion in the vicinity of the Enriquillo-Plantain Garden fault zone, faster than previously estimated and possibly accommodated by folds and faults in the Enriquillo-Plantain Garden fault zone borderlands. Our new and a previous estimate of Gonave-Caribbean plate motion suggest that enough elastic strain accumulates to generate one to two Mw∼ 7 earthquakes per century along the Enriquillo-Plantain Garden and nearby faults of southwest Hispaniola. That the 2010 M= 7.0 Haiti earthquake ended a 240-yr-long period of seismic quiescence in this region raises concerns that it could mark the onset of a new earthquake sequence that will relieve elastic strain that has accumulated since the late 18th century.

Seismic hazard of the Enriquillo–Plantain Garden fault in Haiti inferred from palaeoseismology

The Enriquillo–Plantain Garden fault zone is the primary plate-bounding fault system in Haiti and was initially thought to be responsible for the 2010 earthquake. Palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770, but did not rupture during the 2010 earthquake. The Enriquillo–Plantain Garden fault zone is recognized as one of the primary plate-bounding fault systems in Haiti1,2. The strike-slip fault runs adjacent to the city of Port-au-Prince and was initially thought to be the source of the 12 January 2010, Mw 7.0 earthquake. Haiti experienced significant earthquakes in 1751 and 1770 (refs 3, 4, 5), but the role of the Enriquillo–Plantain Garden fault zone in these earthquakes is poorly known. We use satellite imagery, aerial photography, light detection and ranging (LIDAR) and field investigations to document Quaternary activity on the Enriquillo–Plantain Garden fault. We report late Quaternary, left-lateral offsets of up to 160 m, and a set of small offsets ranging from 1.3 to 3.3 m that we associate with one of the eighteenth century earthquakes. The size of the small offsets implies that the historical earthquake was larger than Mw 7.0, but probably smaller than Mw 7.6. We found no significant surface rupture associated with the 2010 earthquake. The lack of surface rupture, coupled with other seismologic, geologic and geodetic observations6,7, suggests that little, if any, accumulated strain was released on the Enriquillo–Plantain Garden fault in the 2010 earthquake. These results confirm that the Enriquillo–Plantain Garden fault remains a significant seismic hazard.

Haiti After the Earthquake: Eos Interviews Seismologist Eric Calais

Recent earthquakes have jolted Chile and other places around the globe. However, the devastating 12 January 2010 strikeslip earthquake along a 50‐kilometer portion of the Enriquillo—Plantain Garden fault zone (EPGFZ) near Port‐au‐Prince, Haiti, still is strongly resonating, figuratively and literally. The earthquake, of magnitude 7.0 or 7.1, killed more than 220,000 people. The more than 50 aftershocks to date of magnitude 4.5 or greater are part of the process of readjustment of the Earth's crust that could take 2–3 years to reach equilibrium, according to Eric Calais, professor of geophysics in Purdue University's Department of Earth and Atmospheric Sciences and a researcher at the French National Center for Scientific Research (CNRS).

Haiti Earthquake Underscores Need for Better Use of Seismic Information

When Eric Calais, professor of geophysics in Purdue University's Department of Earth and Atmospheric Sciences, first learned about the 12 January strike‐slip earthquake along a portion of the Enriquillo—Plantain Garden fault zone (EPGFZ) in Haiti, he knew right away that it would be a shallow event and a large event, very close to the capital city of Portau‐Prince. Having worked in Haiti, he also was aware that the poor nation lacks seismic and building construction codes. “My immediate reaction was, ‘This is going to be a total nightmare and a huge disaster for Haiti,’” Calais, who also is a researcher at the French National Center for Scientific Research, told Eos.

Actively evolving microplate formation by oblique collision and sideways motion along strike-slip faults: An example from the northeastern Caribbean plate margin

The pattern of folding, faulting, and late Quaternary coral-reef uplift rates in western and central Hispaniola (Haiti and Dominican Republic) suggest that the elongate Gonave microplate, a 190,000-km 2 area of the northeastern Caribbean plate, is in the process of shearing off the Caribbean plate and accreting to the North American plate. Late Cenozoic transpression between the southeastern Bahama Platform and the Caribbean plate in Hispaniola has inhibited the eastward motion of the northeastern corner of the plate. Transpression is manifested in western and central Hispaniola by the formation of regional scale folds that correspond to present-day, anticlinal topographic mountain chains continuous with offshore anticlinal ridges. Areas of most rapid Quaternary uplift determined from onland coral reefs 125 ka and younger, coincide with the axial traces of these folds. Offshore data suggest recent folding and faulting of the seafloor. Onshore reef data do not conclusively require late Quaternary folding, but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the Northwest Peninsula of Haiti (0.37 mm/yr) to to the central part of the coast of western Haiti (0.19 mm/yr) to the south-central part of western Haiti (0 mm/yr). Formation of the 1200-km-long Enriquillo-Plantain Garden-Walton fault zone as a ‘bypass’ strike-slip fault has isolated the southern edge of the Gonave microplate and is allowing continued, unimpeded eastward motion of a smaller Caribbean plate past the zone of late Neogene convergence and Quaternary uplift of coral reefs in Hispaniola. Offshore seismic reflection data from the Jamaica Passage, the marine strait separating Jamaica and Haiti, show that the Enriquillo-Plantain Garden fault zone forms a narrow but deep, active fault-bounded trough beneath the passage. The active fault is continuous with active faults mapped onshore in western Haiti and eastern Jamaica; the bathymetric deep is present because the Jamaica Passage fault segment represents a 50-km-wide, transtensional left-step of the fault trace between Haiti and Jamaica. Onshore satellite imagery and field observations suggest that the Enriquillo-Plantain Garden fault forms a continuous trace extending from central Hispaniola east of Lake Enriquillo, Dominican Republic, to the westernmost end of the southern peninsula of Haiti. The regional lineament corresponds to a recent fault scarp in Quaternary alluvium of the Clonard pull-apart basin in the central part of the southern peninsula of Haiti and suggests that at least this part of the lineament has undergone recent slip. Calmus (1983) has suggested a total offset of 30–50 km of the Enriquillo-Plantain Garden fault zone in the southern peninsula of Haiti using the apparent offset of lithologic units. Seismic reflection data from Lake Enriquillo document recent deformation of Quaternary lake sediments where the lineament crosses the lake. Leveling of the crest of a late Holocene coral reef and associated algal tufa around Lake Enriquillo demonstrate late Holocene vertical movement and tilting in a 1500-m-wide zone parallel to the fault trend. Lateral offset is difficult to show in the Enriquillo Valley area because of rapid recent sedimentation into the valley. The pattern of inactive strike-slip faults and fold belts of Cenozoic age in Cuba and the Yucatan basin suggest that two elongate microplates were sheared off the proto-Caribbean plate and accreted to the North American plate by a similar process in Paleocene and Eocene times. Age of terminal deformation in western, central and eastern Cuba is consistent with southeastward younging and migration of arc collision. The similarity of the size and sequence of events in Cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike-slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas.

North Caribbean neotectonic events: The Trans-Haitian fault system. Tertiary record of an oblique transcurrent shear zone uplifted in Hispaniola

The left-lateral relative motion between the Caribbean and the North American plates has previously been inferred as occurring along a fault zone located north of Hispaniola. East of the northern Dominican Republic, a relatively linear fracture zone (the Septentrional Fault Zone, SFZ) extends into the Puerto Rico subduction zone. Similarly, south of Haiti, the trace of the inactive Enriquillo-Plantain Garden Fault Zone (EPGFZ) extends into the Muertos Trench and may represent a major fault along the plate boundary. Between these two major strike-slip fault systems, the central part of Haiti shows a diffuse fracture zone that trends N130. The chronology of deformation involves an initial Paleocene to Eocene suturing of allochthonous terranes, a Late Miocene development of a strong spaced cleavage within the late Paleocene to Late Miocene strata that overlap the terrane suture, and diffuse Pliocene to Pleistocene strike-slip faulting along traces that reactivate the older spaced cleavage planes. During the Pleistocene, basalts ranging in age from 0.4 to 1.3 Ma were extruded in pull-apart basins associated with N130-trending faults (antithetic features of the SFZ) and N30 normal faults (antecedent synthetic features of the SFZ). This event is coeval with the compression recorded at the Muertos-Beata collision front in the southwestern Dominican Republic. The most recent phase of tectonism involves strong uplifts and broad, open folding along NW-striking axes, which is consistent with the regional maximum deformation pattern predicted for E-W left-lateral shear along the North America—Caribbean plate boundary.