Abstract Central America is a small and culturally homogeneous region that, since the 1990s, has experienced economic and political integration of its six countries, which share the same threats of volcanic eruptions, disastrous earthquakes and tsunamis. The Pacific coastline of 1700 km is common for Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama, and the Pacific subduction zone has the potential for creating huge tsunamis that threaten this coast. In addition to the natural hazard, the growing tourist industry is expanding its infrastructure along the Pacific beaches, which again enhances the exposure and tsunami risk. Even though the 1992 tsunami disaster in Nicaragua did not severely hit the tourist beaches, it raised the risk awareness, and special attention is now given to ‘slow’ earthquakes that may be modest in shaking while still having a large tsunami potential. The tsunami hazard mapping is well advanced in Nicaragua, Costa Rica and El Salvador, and initiatives are ongoing to improve the mapping in all countries. National systems for early warning were established in Nicaragua and El Salvador, while the other four countries rely on rapid information from the Pacific Tsunami Warning Center. Mitigation measures and information campaigns are presently conducted on a national basis in all countries, but a regional centre for early tsunami warning and coordinated information campaigns (CATAC) is expected to become operational in the near future.

Abstract Northern Honduras and its offshore area include an active transtensional margin separating the Caribbean and North American plates. We use deep-penetration seismic-reflection lines combined with gravity and magnetic data to describe two distinct structural domains in the Honduran offshore area: (1) an approximately 120 km-wide Honduran Borderlands (HB) adjacent to the Cayman Trough characterized by narrow rift basins controlled by basement-involving normal faults subparallel to the margin; and (2) the Nicaraguan Rise (NR), characterized by small-displacement normal faulting and sag-type basins influenced by Paleocene–Eocene shelf sedimentation beneath an Oligocene–Recent, approximately 1–2 km-thick carbonate platform. Thinning of continental crust from 25–30 km beneath the NR to 6–8 km beneath the oceanic Cayman Trough is attributed to an Oligocene–Recent phase of transtension. Five tectonostratigraphic phases established in the HB and NR include: (1) a Late Cretaceous uplift in the north and south-dipping thrusting related to the collision in the south, between the Chortis continental block and arc and oceanic plateau rocks of the Caribbean; (2) Eocene sag basins in the NR and minor extension in the HB; two phases (3) and (4) of accelerated extension (transtension) across the subsidence mainly of the HB; and (5) Pliocene–Recent minor fault activity in the HB and a stable carbonate platform in the NR.

Abstract Previous workers, mainly mapping on-land active faults on Caribbean islands, defined the northern Caribbean plate boundary zone as a 200-km-wide and bounded by two active and parallel strike-slip faults: the Oriente fault along the northern edge of the Cayman trough having a GPS rate of 14 mm/yr, and the Enriquillo-Plaintain Garden fault zone (EPGFZ) having a rate of 5-7 mm/yr. In this study, we used 5,000 km of industry and academic data from the Nicaraguan Rise south and southwest of the EPGFZ in the maritime areas of Jamaica, Honduras, and Colombia to define an offshore, 700-km-long, active, left-lateral strike-slip fault in what had been considered previously the stable interior of the Caribbean plate as determined from plate-wide GPS studies. The fault was named by previous workers as the Pedro Banks fault zone (PBFZ) because a 100-km-long segment of the fault forms an escarpment along the Pedro carbonate bank of the Nica-raguan Rise. Two fault segments of the PBFZ are defined: the 400-km-long eastern segment that exhibits large negative flower structures 10-50 km in width; fault segments rupture the sea floor as defined by high resolution 2D seismic data; and a 300-km-long western segment that is defined by a narrow zone of anomalous seismicity first observed by previous workers. The western end of the PBFZ terminates on a Quaternary rift structure, the San Andres rift, associated with Plio-Pleistocene volcanism and thickening trends indicating initial rifting in the late Miocene. The southern end of the San Andreas rift terminates on the western Hess fault which also exhibits active strands consistent with left-lateral, strike-slip faults. The total length of the PBFZ-San Andres rift-Southern Hess escarpment fault is 1,200 km and traverses the entire western end of the Caribbean plate. Our interpretation is similar to previous models that have proposed the “stable” western Caribbean plate is broken by this fault, the rate of displacement of which is less than the threshold recognizable from the current GPS network (~3 mm/yr). The late Miocene age of the fault indicates it may have activated during the late Miocene to recent His-paniola-Bahamas oblique collision event.

Velocities from six continuous and 14 campaign sites within the boundaries of the Caribbean plate, including eight new sites from previously unsampled areas of Honduras and Nicaragua at the western edge of the Caribbean plate, are described and tested for their consistency with Caribbean–North America plate motion and a rigid Caribbean plate model. Sites in central Honduras and Guatemala move 3–8 mm yr −1 westward with respect to the Caribbean plate interior, consistent with distributed east-to-west extension in Guatemala and the western two-thirds of Honduras. A site in southern Jamaica moves 8 ± 1 mm yr −1 westward relative to the Caribbean plate interior, indicating that most or all of Jamaica is unsuitable for estimating Caribbean plate motion. Two sites in southern Hispaniola also exhibit anomalous motions relative to the plate interior, consistent with a tectonic bias at those sites. An inversion of the velocities for 15 sites nominally located in the plate interior yields a well-constrained Caribbean plate angular velocity vector that predicts motion similar to previously published models. Data bootstrapping indicates that the solution is robust to better than 1 mm yr −1 with respect to both the site velocities that are used to estimate the plate angular velocity and the site velocity uncertainties. That velocities at seven of eight GPS sites in eastern Honduras and Nicaragua are consistent with the motions of sites elsewhere in the plate interior indicates that much or all of eastern Honduras and Nicaragua move with the plate interior within the 1–2 mm yr −1 resolution of our data. It further suggests that the morphologically prominent, but aseismic Guayape fault of eastern Honduras is inactive. Tests for possible east-to-west deformation across the Beata Ridge and Lower Nicaraguan Rise in the plate interior establish a 95% upper bound of ∼2 mm yr −1 for any deformation across the two features, significantly slower than a published estimate of 9.0 ± 1.5 mm yr −1 during the past 23 Ma for deformation across the Beata Ridge.

Divergence, expressed as the angle between the plate motion vector and the azimuth of a plate margin fault, has been proposed to explain development of contrasting styles of transtensional deformation along transform margins. We present the western North America–Caribbean plate margin as a test of this hypothesis. Here, geologic, earthquake, marine geophysical, and remote sensing data show two distinct structural styles: (1) east-west extension along north-trending rifts normal to the plate margin in the western study area (western Honduras and southern Guatemala); and (2) NNW-SSE transtension along rifts subparallel to the plate margin in the eastern study area (northern Honduras and offshore Honduran borderlands region). Orientations of rifts in each area coincide with the angle of divergence between the GPS-derived plate motion vector and the azimuth of the plate boundary fault, such that the western zone of east-west extension has an angle >10°, while the eastern zone of NNW-SSE extension occurs when the angle of divergence is between 5° and 10°. A narrow transition area in north-central Honduras separates the plate boundary–normal rifts of western Honduras from the plate boundary–parallel rifts to the east. Faults of the offshore Honduran borderlands extend onshore into the Nombre de Dios range and Aguan Valley of northern Honduras where tectonic geomorphology studies show pervasive oblique-slip faulting with active left-lateral river offsets and active uplift of stream reaches. Offshore, exploration seismic data tied to wells in the Honduran borderlands reveal active submarine faults bounding asymmetric half-grabens filled by middle Miocene clastic wedges with continued clastic deposition into Pliocene-Pleistocene. The north-trending rifts of western Honduras form discontinuous half-grabens that cut late Miocene ignimbrite strata. Plate reconstructions indicate the north-trending rifts of western Honduras developed in response to increased interplate divergence as the western margin of the Caribbean plate shifted from the Jocotan fault to the Polochic fault during the middle Miocene.

An aeromagnetic survey of Honduras and its northeastern Caribbean coastal area covering a continuous area of 137,400 km 2 was acquired by the Honduran government in 1985 and provided to the University of Texas at Austin for research purposes in 2002. We correlate regional and continuous aeromagnetic features with a compilation of geologic data to reveal the extent, structural grain, and inferred boundaries of tectonic terranes that compose the remote and understudied, Precambrian-Paleozoic continental Chortis block of Honduras. A regional geologic map and a compilation of isotopic age dates and lead isotope data are used in conjunction with and geo-referenced to the aero-magnetic map. These combined data provide a basis for subdividing the 531,370 km 2 Chortis block into three tectonic terranes with distinctive aeromagnetic expression, lithologies, structural styles, metamorphic grade, isotopically and paleontologically determined ages, and lead isotope values: (1) The Central Chortis terrane occupies an area of 110,600 km 2 , exhibits a belt of roughly east-west–trending high magnetic values, and exposes small, discontinuous outcrops of Grenville to Paleozoic continental metamorphic rocks including greenschist to amphibolite grade phyllite, schist, gneiss, and orthogneiss that have been previously dated in the range of 1 Ga to 222 Ma; the northern 59,990 km 2 margin of the Central Chortis terrane along the northern Caribbean coast of Honduras exhibits an irregular pattern of east-west–trending magnetic highs and lows that correlates with an east-west–trending belt of early Paleozoic to Tertiary age metamorphic rocks intruded by Late Cretaceous and early Cenozoic plutons in the range of 93.3–28.9 Ma. (2) The Eastern Chortis terrane occupies an area of 185,560 km 2 , exhibits belts of roughly northeast-trending high magnetic values, and correlates with outcrops of folded and thrusted Jurassic metasedimentary phyllites and schists forming a greenschist-grade basement; we propose that the Eastern and Central terranes are distinct terranes based on the strong differences in their structural style and aeromagnetic grain, sedimentary thickness, metamorphic grade, and lead isotope values. (3) The Southern Chortis terrane occupies an area of 120,100 km 2 , contains one known basement outcrop of metaigneous rock, exhibits a uniformly low magnetic intensity that contrasts with the rest of the Chortis block, and is associated with an extensive area of Miocene pyroclastic strata deposited adjacent to the late Cenozoic Central American volcanic arc. The outlines of the terranes as constrained by the aeromagnetic, lithologic, age, and lead isotope data are restored to their pre–early Eocene position along the southwestern coast of Mexico by a 40° clockwise rotation and 1100 km of documented post–early Eocene (ca. 43 Ma) left-lateral offset along the strike-slip faults of the northern Caribbean strike-slip plate boundary. The inner continental and outboard oceanic terranes of Chortis and the 120,100 km 2 Siuna terrane to the south trend roughly north-south and align with terranes of similar magnetic trend, lithology, age, and crustal character in southwestern Mexico. Additional progress in mapping and isotopic dating is needed for the proposed Chortis terranes in Honduras in order to constrain this proposed position against much better mapped and dated rocks in southwestern Mexico.

This study describes the geology of a well-exposed but previously unmapped section of Paleozoic–early Cenomanian metamorphic, sedimentary, and igneous rocks in the Frey Pedro study area of the Agalta Range of east-central Honduras. The objective of the study is to use these new structural, stratigraphic, biostratigraphic, and geochemical data to better constrain the geologic and tectonic history of this part of the Chortis block during the period of time from Aptian to early Cenomanian. The study revealed that the topographic Agalta Range exposes a thick stratigraphic section (3.5 km) deposited in an Albian-Aptian intra-arc rift and on the rift shoulders. This rift feature, named here the Agua Blanca rift, presently trends northwest and is parallel to three other belts of deformed Cretaceous rocks in Honduras (the Comayagua, Minas de Oro, and Montaña de la Flor belts) that also may correspond to Cretaceous intra-arc rifts produced during the same phase of intra-arc extension. These other three deformed belts are west of the Agalta Range and also form topographically elevated mountain ranges. Albian-Aptian calc-alkaline volcanic rocks and pyroclastic flows of the Manto Formation record arc affinity, while the volcaniclastic wedges of the Tayaco Formation record syn-rift deposition. These rift and arc-related units occupy the stratigraphic position between two major, extensive, shallow-water carbonate units, the lower and upper Atima Formations, also of middle Cretaceous age. Thickening of volcaniclastic rocks of the Tayaco Formation strata in the Agua Blanca rift accompanied erosion of the adjacent rift shoulders and eruption of Manto calc-alkaline volcanic rocks both within and adjacent to the Agua Blanca rift. The Agua Blanca intra-arc rift was inverted by a regional shortening event presumably in the Late Cretaceous. Rocks within the rift were intensely shortened, while rocks on the rift shoulders were shortened less because they are underlain by more competent metamorphic basement rocks. In order to better understand the Aptian–early Cenomanian tectonic setting for intra-arc rifting and subsequent rift inversion on the Chortis block, we reconstructed the Chortis block relative to the terranes studied by previous workers in southern Mexico. Five geologic and tectonic features were selected for realigning the two now widely separated areas: (1) areas of Precambrian basement outcrops, (2) areas of similar Mesozoic stratigraphy, (3) aligned trends of Mesozoic volcanic arc rocks exhibiting a similar arc geochemistry, (4) aligned trends of Late Cretaceous folds and thrusts, and (5) alignment of magnetic boundary.

We document a previously unrecognized, thin-skinned arc-continental collisional zone, termed here the Colon fold-thrust belt, which trends northeastward for 350 km near the Honduras-Nicaragua border region. The Colon belt occurs in three collinear segments: (1) a 200-km-long belt of remote but well-exposed Jurassic–Late Cretaceous rock outcrops described from original geologic mapping presented in this study; (2) a 75-km-long subsurface belt of Jurassic–Late Cretaceous rocks known from onland seismic reflection studies and exploration drilling for oil; and (3) an offshore 75-km-long subsurface belt of Late Cretaceous to Eocene rocks known from exploration studies. These three segments share a continuity of the deformation front and associated folds, as well as a similar timing of fold-thrust deformation (segment one: post-Campanian; segment two: post–Late Cretaceous; segment three: post-Cretaceous and possible to Eocene); and all segments display southeastward-dipping thrusts and related northeastward-verging folds that structurally elevate Cretaceous rocks. The structural position of the Siuna belt of oceanic island arc affinity to the south of the Colon fold-thrust belt, its association with calc-alkaline volcanic rocks of the Caribbean arc, and its Campanian (75 Ma) emplacement age, suggest that the Siuna belt was overthrust to the north and northwest onto the hanging wall of the Colon fold-thrust belt. The northwestward-transported Colon fold-thrust belt and adjacent Siuna belt document a Late Cretaceous collisional event between a south-facing continental margin of the Chortis block of northern Central America and an eastward and north-eastward-moving, Early to Late Cretaceous Caribbean arc system.

Ignimbrites, as widespread sheets tens of meters thick, form the Central American Tertiary Ignimbrite Province. Geochemical data were collected from 99 Cenozoic marine ash layers within Caribbean Sea sediments, 76 vitrophyres, and 21 mafic lavas from Nicaragua and Honduras. Two major eruptive periods, one in the Eocene and one in the Miocene, have been broadly identified. 40 Ar/ 39 Ar laser fusion ages, determined from sanidine or plagioclase in 10 of the vitrophyre samples, have been interpreted to indicate that the bulk of the younger group of ignimbrites formed largely in the middle Miocene during a 3.5-m.y. period between 16.9 and 13.4 Ma. Modeling indicates that initial melts were from a normal mid-oceanic-ridge basalt (N-MORB)–type source, rather than the enriched mid-oceanic-ridge basalt (E-MORB)–type source postulated for the modern arc. All of the ignimbrites analyzed have 87 Sr/ 86 Sr isotope values ( 87 Sr/ 86 Sr = 0.7040–0.7069) within the range of continental crust. Trace element trends are similar to those estimated for lower continental crust. Assimilation– fractional crystallization and melt mixing models produce trends that are consistent with ignimbrite compositions. This evidence is consistent with a large influence of continental crust in the ignimbrite formation. In addition, the ignimbrite magmas, like those of the modern arc, have also been determined to have been contaminated by sediment-derived fluids. Abnormally rapid subduction of the Farallon-Cocos plate, which coincides with the formation of the ignimbrites, may have resulted in their generation. A slab gap that currently exists beneath the modern arc may be the cause of a change in source from N-MORB to E-MORB by allowing rising asthenospheric material to “recharge” the mantle wedge in trace elements that had been depleted prior to the gap formation.

Ignimbrites are deposits resulting from the eruption of volatile-rich, silicic magma. Few geochemical or petrological studies have been done concerning the Tertiary Ignimbrite Province of Central America in Honduras and Nicaragua. Previous work, using ages and geographical proximity, suggested that tephra layers recovered during Ocean Drilling Program (ODP) Leg 165 in the western Caribbean Sea were associated with deposits from explosive eruptions in Central America. A total of 112 marine tephra and 79 terrestrial samples from Nicaragua and Honduras were analyzed during this study. An electron microprobe was used for major oxides, and laser inductively coupled plasma–mass spectrometry (ICP-MS) was used for trace elements. The rare earth elements (REEs), due to their resistance to weathering, were used to correlate the marine tephra with the terrestrial samples. Cluster analysis resulted in the division of the samples into 6 geochemical groups. Visual inspection of these groups resulted in the reclassification of these 6 into 14 distinct geochemical groups. Each one of these geochemical groups displays unique REE trends relative to each other. The trends vary, relative to enriched mid-ocean-ridge basalt (EMORB), from strongly light (L) REE enriched with moderate to large, negative Eu anomalies, to nearly equal EMORB values without any Eu anomalies, to enriched REE with positive Eu anomalies. All but two groups consist of both marine and terrestrial samples. The geochemical correlation is strengthened using factor analysis, in which the REE values for each sample were reduced to two factors and replotted. Each group plots in a distinct field. The Lesser Antilles can be ruled out as contributing to the western Caribbean tephra due to the lack of any large-volume ignimbrite sheets within the arc, as well as the distinctly different REE trends of the magmas. The Sierra Madre Igneous Province in México is also ruled out as a potential source, due mainly to a significant age difference between Sierra Madre ignimbrites and the Caribbean Sea tephra layers. Besides the strong similarities in REE patterns, several of the groups and subgroups are geographically limited in extent, which might imply a specific group source location.

Edifice-collapse phenomena have, to date, received relatively little attention in Central America, although ∼40 major collapse events (≥0.1 km 3 ) from about two dozen volcanoes are known or inferred in this volcanic arc. Volcanoes subjected to gravitational failure are concentrated at the arc's western and eastern ends. Failures correlate positively with volcano elevation, substrate elevation, edifice height, volcano volume, and crustal thickness and inversely with slab descent angle. Collapse orientations are strongly influenced by the direction of slope of the underlying basement, and hence are predominately perpendicular to the arc (preferentially to the south) at its extremities and display more variable failure directions in the center of the arc. The frequency of collapse events in Central America is poorly constrained because of the lack of precise dating of deposits, but a collapse interval of ∼1000–2000 yr has been estimated during the Holocene. These high-impact events fortunately occur at low frequency, but the proximity of many Central American volcanoes to highly populated regions, including some of the region's largest cities, requires evaluation of their hazards. The primary risks are from extremely mobile debris avalanches and associated lahars, which in Central America have impacted now-populated areas up to ∼50 km from a source volcano. Lower probability risks associated with volcanic edifice collapse derive from laterally directed explosions and tsunamis. The principal hazards of the latter here result from potential impact of debris avalanches into natural or man-made lakes. Much work remains on identifying and describing debris-avalanche deposits in Central America. The identification of potential collapse sites and assessing and monitoring the stability of intact volcanoes is a major challenge for the next decade.