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Uri S. ten Brink

Publications and source records attributed to Uri S. ten Brink.

At least 73 records · Page 4Linked to original sources
USGS2012

Rift flank uplifts and Hinterland Basins: Comparison of the Transantarctic Mountains with the Great Escarpment of southern Africa

Uplifted rift margins are a common feature of continents and oceans. Two variants of rift flank morphologies have been recognized: One in which the topography warps down from an inland high toward the continental margin, and one where the tropographic peak lies close to the continental margin. The Great Escarpment of southern Africa and the Transantarctic Mountains are examples of the first and the second variants of rift flanks, respectively. Both rift flanks are bordered on their landward side by broad continental basins: the Kalahari and the Wilkes hinterland basins. If these basins are interpreted as flexural “outer lows” that deepen in unison with the uplift of the rift flanks, the lithosphere on the uplifted side is very rigid in both cases (elastic thickness T e of 100 ± 20 km for southern Africa and 110 ± 20 km for East Antarctica). We suggest that the variation in rift flank morphology is caused by the isostatic response to uplift forces of elastic plates sharing different boundary conditions. We model the uplift of the Transantarctic Mountains as an upward deflection of an elastic plate which is broken at the front of the Transantarctic Mountains, and we model the uplift of the Great Escarpment as an upward deflection of a continuous elastic plate that is modified by the downward load of sediments on the continental margin. Although the Transantarctic Mountain uplift is young (60–0 Ma) and the southern African uplift is old (<100 Ma), the different isostatic responses of the two margins are not a function of age, because most loading (sedimentation) and unloading (erosion) took place shortly after rifting. Detailed modeling of topography, gravity, geological markers, and the locations of depocenters suggests that lithospheric rigidity decreases under the Transantarctic Mountains, whereas in southern Africa the decrease occurs not under the Great Escarpment but far seaward under the continental shelf and slope. If the distribution of lithospheric rigidity is indicative of the thermal regime of the lithosphere, then uplifted rift flanks are not always underlain by a thermal anomaly. This and other geological evidence indicate that a single mechanism cannot explain the uplift of both the Antarctic and the African margins.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Three-dimensional modeling of pull-apart basins: implications for the tectonics of the Dead Sea Basin

We model the three-dimensional (3-D) crustal deformation in a deep pull-apart basin as a result of relative plate motion along a transform system and compare the results to the tectonics of the Dead Sea Basin. The brittle upper crust is modeled by a boundary element technique as an elastic block, broken by two en echelon semi-infinite vertical faults. The deformation is caused by a horizontal displacement that is imposed everywhere at the bottom of the block except in a stress-free &ldquo;shear zone&rdquo; in the vicinity of the fault zone. The bottom displacement represents the regional relative plate motion. Results show that the basin deformation depends critically on the width of the shear zone and on the amount of overlap between basin-bounding faults. As the width of the shear zone increases, the depth of the basin decreases, the rotation around a vertical axis near the fault tips decreases, and the basin shape (the distribution of subsidence normalized by the maximum subsidence) becomes broader. In contrast, two-dimensional plane stress modeling predicts a basin shape that is independent of the width of the shear zone. Our models also predict full-graben profiles within the overlapped region between bounding faults and half-graben shapes elsewhere. Increasing overlap also decreases uplift near the fault tips and rotation of blocks within the basin. We suggest that the observed structure of the Dead Sea Basin can be described by a 3-D model having a large overlap (more than 30 km) that probably increased as the basin evolved as a result of a stable shear motion that was distributed laterally over 20 to 40 km.

Dead Sea Basin↗
USGS2012

Plate interaction in the NE Caribbean subduction zone from continuous GPS observations

Kinematic similarities between the Sumatra and Puerto Rico Trenches highlight the potential for a mega-earthquake along the Puerto Rico Trench and the generation of local and trans-Atlantic tsunamis. We used the horizontal components of continuous GPS (cGPS) measurements from 10 sites on NE Caribbean islands to evaluate strain accumulation along the North American (NA) - Caribbean (CA) plate boundary. These sites move westward and slightly northward relative to CA interior at rates &le;2.5 mm/y. Provided this motion originates in the subduction interface, the northward motion suggests little or no trench-perpendicular thrust accumulation and may in fact indicate divergence north of Puerto Rico, where abnormal subsidence, bathymetry, and gravity are observed. The Puerto Rico Trench, thus, appears unable to generate mega-earthquakes, but damaging smaller earthquakes cannot be discounted. The westward motion, characterized by decreasing rate with distance from the trench, is probably due to eastward motion of CA plate impeded at the plate boundary by the Bahamas platform. Two additional cGPS sites in Mona Passage and SW Puerto Rico move to the SW similar to Hispaniola and unlike the other 10 sites. That motion relative to the rest of Puerto Rico may have given rise to seismicity and normal faults in Mona Rift, Mona Passage, and SW Puerto Rico.

Geophysical Research Letters↗
USGS2012

Significant earthquakes on the Enriquillo fault system, Hispaniola, 1500-2010: Implications for seismic hazard

Historical records indicate frequent seismic activity along the north-east Caribbean plate boundary over the past 500 years, particularly on the island of Hispaniola. We use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 Haiti earthquakes to derive an intensity attenuation relation for Hispaniola. The intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments. Here we describe a sequence of devastating earthquakes on the Enriquillo fault system in the eighteenth century. An intensity magnitude M I 6.6 earthquake in 1701 occurred near the location of the 2010 Haiti earthquake, and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake. A series of large earthquakes migrating from east to west started with the 18 October 1751 M I 7.4–7.5 earthquake, probably located near the eastern end of the fault in the Dominican Republic, followed by the 21 November 1751 M I 6.6 earthquake near Port-au-Prince, Haiti, and the 3 June 1770 M I 7.5 earthquake west of the 2010 earthquake rupture. The 2010 Haiti earthquake may mark the beginning of a new cycle of large earthquakes on the Enriquillo fault system after 240 years of seismic quiescence. The entire Enriquillo fault system appears to be seismically active; Haiti and the Dominican Republic should prepare for future devastating earthquakes.

Hispaniola↗
USGS2012

Submarine slides north of Puerto Rico and their tsunami potential

New multibeam bathymetry of the entire Puerto Rico trench reveals numerous retrograde slope failures at various scales at the edge of the carbonate platform north of Puerto Rico and the Virgin Islands. The slumped material comprises carbonate blocks, which fail, at least in initial stages, as a coherent rock mass. This, combined with the fact that the edge of the carbonate platform is steeper than most continental slopes, indicates a higher potential for tsunami run-up than along many other U.S. coasts. The style of slope failure appears to be rock falls, slide blocks and debris avalanches. Secondary failure of the failed carbonate products and of the underlying forearc sediments and rocks may lead to debris flows and turbidity flows. Fissures, discovered in the ocean floor near the edge of the platform, indicate that the process is expected to continue in the future. One of the slope failures, the Arecibo amphitheater, previously thought to represent a single giant slide with a volume of 900-1500 cu. km, appears to comprise smaller failures. The expected maximum tsunami run-up on the northern coast of Puerto Rico from one of these slope failures is <20 m, much lower than previously estimated. A recurrence rate of 100s kyr was calculated for the largest observed failures along the edge of the carbonate platform north of Puerto Rico using simple assumptions. Smaller landslides would presumably occur at a higher recurrence rate. Elsewhere around the island, a 20-km wide failure scarp was discovered in the Upper Mona rift and could be associated with the 1918 tsunami and earthquake that hit northwestern Puerto Rico. Large slope failures were also discovered for the first time on the northern side of the Puerto Rico trench. Because Puerto Rico trench slides occur at large water depths (~6000 m), have large horizontal and vertical dimensions, and the directivity from tsunamis emanating from these slides is toward Puerto Rico, they may be of particular concern and may necessitate further study.

Puerto Rico↗
USGS2012

Geometry and subsidence history of the Dead Sea basin: A case for fluid-induced mid-crustal shear zone?

Pull‐apart basins are narrow zones of crustal extension bounded by strike‐slip faults that can serve as analogs to the early stages of crustal rifting. We use seismic tomography, 2‐D ray tracing, gravity modeling, and subsidence analysis to study crustal extension of the Dead Sea basin (DSB), a large and long‐lived pull‐apart basin along the Dead Sea transform (DST). The basin gradually shallows southward for 50 km from the only significant transverse normal fault. Stratigraphic relationships there indicate basin elongation with time. The basin is deepest (8–8.5 km) and widest (∼15 km) under the Lisan about 40 km north of the transverse fault. Farther north, basin depth is ambiguous, but is 3 km deep immediately north of the lake. The underlying pre‐basin sedimentary layer thickens gradually from 2 to 3 km under the southern edge of the DSB to 3–4 km under the northern end of the lake and 5–6 km farther north. Crystalline basement is ∼11 km deep under the deepest part of the basin. The upper crust under the basin has lower P wave velocity than in the surrounding regions, which is interpreted to reflect elevated pore fluids there. Within data resolution, the lower crust below ∼18 km and the Moho are not affected by basin development. The subsidence rate was several hundreds of m/m.y. since the development of the DST ∼17 Ma, similar to other basins along the DST, but subsidence rate has accelerated by an order of magnitude during the Pleistocene, which allowed the accumulation of 4 km of sediment. We propose that the rapid subsidence and perhaps elongation of the DSB are due to the development of inter‐connected mid‐crustal ductile shear zones caused by alteration of feldspar to muscovite in the presence of pore fluids. This alteration resulted in a significant strength decrease and viscous creep. We propose a similar cause to the enigmatic rapid subsidence of the North Sea at the onset the North Atlantic mantle plume. Thus, we propose that aqueous fluid flux into a slowly extending continental crust can cause rapid basin subsidence that may be erroneously interpreted as an increased rate of tectonic activity.

Dead Sea shoreline↗
USGS2012

Accounts of damage from historical earthquakes in the northeastern Caribbean to aid in the determination of their location and intensity magnitudes

Earthquakes have been documented in the northeastern Caribbean since the arrival of Columbus to the Americas; written accounts of these felt earthquakes exist in various parts of the world. To better understand the earthquake cycle in the Caribbean, the records of earthquakes in earlier catalogs and historical documents from various archives, which are now available online, were critically examined. This report updates previous catalogs of earthquakes, in particular earthquakes in Hispaniola, to give to the public the most comprehensive documentation of earthquake damage and to further the understanding of the earthquake cycle in the northeastern Caribbean. Documentation of an event in the past depended on the population and political trends of the island, and the availability of historical documents is limited by the physical resource digitization schedule and by the copyright laws of each archive. Examples of documents accessed are governors' letters, newspapers, and other circulars published within the Caribbean, North America, and Western Europe. Key words were used to search for publications that contain eyewitness accounts of various large earthquakes. Finally, this catalog provides descriptions of damage to buildings used in previous studies for the estimation of moment intensity (MI) and location of significantly damaging or felt earthquakes in Hispaniola and in the northeastern Caribbean, all of which have been described in other studies.

Open-File Report↗
USGS2011

Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region

We evaluate the long-term seismic activity of the North-American/Caribbean plate boundary from 500 years of historical earthquake damage reports. The 2010 Haiti earthquakes and other earthquakes were used to derive regional attenuation relationships between earthquake intensity, magnitude, and distance from the reported damage to the epicenter, for Hispaniola and for Puerto Rico and the Virgin Islands. The attenuation relationship for Hispaniola earthquakes and northern Lesser Antilles earthquakes is similar to that for California earthquakes, indicating a relatively rapid attenuation of damage intensity with distance. Intensities in Puerto Rico and the Virgin Islands decrease less rapidly with distance. We use the intensity-magnitude relationships to systematically search for the location and intensity magnitude MI which best fit all the reported damage for historical earthquakes. Many events occurred in the 20th-century along the plate-boundary segment from central Hispaniola to the NW tip of Puerto Rico, but earlier events from this segment were not identified. The remaining plate boundary to the east to Guadeloupe is probably not associated with M > 8 historical subduction-zone earthquakes. The May 2, 1787 earthquake, previously assigned an M 8–8.25, is probably only M I 6.9 and could be located north, west or SW of Puerto Rico. An M I 6.9 earthquake on July 11, 1785 was probably located north or east of the Virgin Islands. We located M I < 8 historical earthquakes on April 5, 1690, February 8, 1843, and October 8, 1974 in the northern Lesser Antilles within the arc. We speculate that the December 2, 1562 (M I 7.7) and May 7, 1842 (M I 7.6) earthquakes ruptured the Septentrional Fault in northern Hispaniola. If so, the recurrence interval on the central Septentrional Fault is ~300 years, and only 170 years has elapsed since the last event. The recurrence interval of large earthquakes along the Hispaniola subduction segment is likely longer than the historical record. Intra-arc M ≥ 7.0 earthquakes may occur every 75–100 years in the 410-km-long segment between the Virgin Islands and Guadeloupe.

Caribbean Sea↗
USGS2011

A reevaluation of the Munson-Nygren-Retriever submarine landslide complex, Georges bank lower slope, western north Atlantic

The Munson-Nygren-Retriever (MNR) landslide complex is a series of distinct submarine landslides located between Nygren and Powell canyons on the Georges Bank lower slope. These landslides were first imaged in 1978 using widely-spaced seismic reflection profiles and were further investigated using continuous coverage GLORIA sidescan imagery collected over the landslide complex in 1987. Recent acquisition of highresolution multibeam bathymetry across these landslides has provided an unprecedented view of their complex morphology and allows for a more detailed investigation of their evacuation and deposit morphologies and sizes, modes of failure, and relationship to the adjacent sections of the margin, including the identification of an additional landslide within the MNR complex, referred to here as the Pickett slide. The evacuation zone of these landslides covers an area of approximately 1,780 km2 . The headwalls of these landslides are at a depth of approximately 1,800 m, with evacuation extending for approximately 60 km downslope to the top of the continental rise. High-relief debris deposits, in the form of blocks and ridges, are present down the length of the majority of the evacuation zones and within the deposition area at the base of the slope. On the continental rise, the deposits from each of the most recent failures of the MNR complex landslides merge with debris from earlier continental slope failures, canyon and alongslope derived deposits, and prominent upper-rise failures.

Advances in Natural and Technological Hazards Rese↗
USGS2011

New seafloor map of the Puerto Rico Trench helps assess earthquake and tsunami hazards

The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure l). The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S.Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands [McCann et al., 2004]. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918 [Mercado and McCann, 1998]. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico [Mercado et al., 2002; Schwab et al., 1991],although their ages are unknown.

Puerto Rico Trench↗
USGS2011

Survey explores active tectonics in northeastern Caribbean

There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and tsunami hazard assessments [e.g., ten Brink and Lin , 2004; ten Brink et al ., 2004; Grindlay et al ., 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary. Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies.

Eos, Transactions, American Geophysical Union↗
USGS2011

Exploring active tectonics in the Dominican Republic

The devastating 12 January 2010 Haiti earthquake ( M = 7.0), which killed an estimated 230,000 people and caused extensive damage to homes and buildings, drew attention to the crucial need for improved knowledge of the active tectonics of the Caribbean region. But even before this disastrous event, interest in understanding the active and complex northeastern Caribbean plate boundary had been increasing, because this region has experienced significant seismic activity during the past century and has an extensively documented record of historical seismicity and tsunamis. Moreover, this is an easily accessible region in which to study the continuity of seismic faults offshore and to try to understand the transitions between strike-slip and convergent tectonic regimes. Interest in the region has led to several studies that have improved scientists' knowledge of subduction zone tectonics and earthquake and tsunami hazard assessments [ Mann et al., 2002; ten Brink et al., 2006, 2009; Grindlay et al., 2005; Manaker et al., 2008; Granja Bruña et al., 2009; Mondziel et al., 2010].

Eos Science News↗
USGS2011

Images of crust beneath southern California will aid study of earthquakes and their effects

The Whittier Narrows earthquake of 1987 and the Northridge earthquake of 1991 highlighted the earthquake hazards associated with buried faults in the Los Angeles region. A more thorough knowledge of the subsurface structure of southern California is needed to reveal these and other buried faults and to aid us in understanding how the earthquake-producing machinery works in this region.

California↗
USGS2011

Urban seismic experiments investigate Seattle fault and basin

In the past decade, Earth scientists have recognized the seismic hazards that crustal faults and sedimentary basins pose to Seattle, Washington (Figure 1). In 1998, the US. Geological Survey and its collaborators initiated a series of urban seismic studies of the upper crust to better map seismogenic structures and sedimentary basins in the Puget Lowland. These studies are called the Seismic Hazard Investigations of Puget Sound (SHIPS). In March 1998, we conducted our first SHIPS study, an investigation of the upper crustal structure of the Puget Lowland, using marine airgun sources and land recorders [ Fisher et al. , 1999].The study was nicknamed Wet SHIPS. In September 1999, we obtained a seismic refraction line to study the upper crustal structure in the Seattle area in a land-based study nicknamed Dry SHIPS [ Brocher et al. , 2000] (Figure 1). In March 2000, we recorded the demolition of the Seattle Kingdome sports stadium using a dense array of seismic recorders for a detailed site response study; this study was nicknamed Kingdome SHIPS (Figure 1).

Washington↗
USGS2010

Gravity modeling of the Muertos Trough and tectonic implications (north-eastern Caribbean)

The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate geometry difficult. In addition, the compressive deformational features observed in the upper crust and sandbox kinematic modeling do not necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate's interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N-S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8?? to 30?? reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin. ?? 2010 Springer Science+Business Media B.V.

Marine Geophysical Research↗
USGS2010

Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands

Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to hundreds of meters perpendicular to a 2-km stretch of Anegada’s windward shore. Remnants of the breached ridges stand 3 m above modern sea level, and ridges seaward of the breaches rise 2.2–3.0 m high. The overwash probably exceeded those heights when cutting the breaches by overtopping and incision of the beach ridges. Much of the sand-and-shell sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand of the breached ridges. This sand extends as much as 1.5 km to the south of the breached ridges. It tapers southward from a maximum thickness of 40 cm, decreases in estimated mean grain size from medium sand to very fine sand, and contains mud laminae in the south. The sand-and-shell sheet also contains mollusks—cerithid gastropods and the bivalve Anomalocardia—and angular limestone granules and pebbles. The mollusk shells and the lime-mud cap were probably derived from a marine pond that occupied much of Anegada’s interior at the time of overwash. The boulders and cobbles, nearly all composed of limestone, form fields that extend many tens of meters generally southward from limestone outcrops as much as 0.8 km from the nearest shore. Soon after the inferred overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats and evaporite crusts. This environmental change, which has yet to be reversed, required restriction of a former inlet or inlets, the location of which was probably on the island’s south (lee) side. The inferred overwash may have caused restriction directly by washing sand into former inlets, or indirectly by reducing the tidal prism or supplying sand to post-overwash currents and waves. The overwash happened after A.D. 1650 if coeval with radiocarbon-dated leaves in the mud cap, and it probably happened before human settlement in the last decades of the 1700s. A prior overwash event is implied by an inland set of breaches. Hypothetically, the overwash in 1650–1800 resulted from the Antilles tsunami of 1690, the transatlantic Lisbon tsunami of 1755, a local tsunami not previously documented, or a storm whose effects exceeded those of Hurricane Donna, which was probably at category 3 as its eye passed 15 km to Anegada’s south in 1960.

Natural Hazards↗
USGS2010

Synthesis of crustal seismic structure and implications for the concept of a slab gap beneath Coastal California

Compilation of seismic transects across the central and northern California Coast Ranges provides evidence for the widespread tectonic emplacement beneath the margin of a slab of partially subducted oceanic lithosphere. The oceanic crust of this lithosphere can be traced landward from the former convergent margin (fossil trench), beneath the Coast Ranges, to at least as far east as the Coast Range/Great Valley boundary. Comparison of measured shear and compressional wave velocities in the middle crust beneath the Hayward fault with laboratory measurements suggests that the middle crust is a diabase (oceanic crust). Both of these observations are consistent with recent models of the high heat flow and age progression of Neogene volcanism along the Coast Ranges based on tectonic emplacement (stalling) of young, hot oceanic lithosphere beneath the margin, but appear to contradict the major predictions of the slab-gap or asthenospheric-window model. Finally, the Neogene volcanism and major strike-slip faults in the Coast Ranges occur within the thickest regions (>14 km thick) of the forearc, suggesting that the locations of Cenozoic volcanism and faulting along the margin are structurally controlled by the forearc thickness rather than being determined by the location of a broad slab gap.

International Geology Review↗