Recent observations of the deformational features on the Muertos compressive margin together with... more Recent observations of the deformational features on the Muertos compressive margin together with sandbox kinematic and gravity modeling question the hypothesized subduction of the Caribbean plate's interior beneath the eastern Greater Antilles island arc. With the aim of testing such subduction, we carried out a wide-angle seismic transect across the widest part of the Muertos compressive margin (longitude 69°W) in the spring of 2009. Shots were fired along the 200 km transect every 90 seconds from the R/V Hesperides' 3850 cubic inches water-gun array, which, towed at 5 knots, resulted in a shot spacing of ~ 230 m. The seismic signal was recorded by five ocean-bottom seismometers deployed at distance intervals from 30 to 50 km. Adjacent reprocessed reflection seismic lines and previous works provided an initial model of the sediment column and the geometry of upper crustal reflectors. A 2-D forward ray-tracing model of the wide-angle transect outlines the broad-scale crusta...
Eos, Transactions American Geophysical Union, 1999
A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reve... more A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reveal much new information about the earthquake threat to U.S. and Canadian urban areas there. A disastrous earthquake is a very real possibility in the region.The survey, known as the Seismic Hazards Investigation in Puget Sound (SHIPS), engendered close cooperation among geologists, biologists, environmental groups, and
As it is known, tsunamis have various general generating mechanisms associated with earthquakes, ... more As it is known, tsunamis have various general generating mechanisms associated with earthquakes, landslides/slumps and volcanic processes. Active tectonics along the north-eastern Caribbean plate is the principal cause de tsunami in the eastern Greater Antilles islands. In this area, earthquake and tsunami record suggest that the main tsunami sources are large shallow earthquakes (6.5) in submarine areas, which can yield
A crustal transect across the 1994 Northridge earthquake region was completed in 1999 with the ac... more A crustal transect across the 1994 Northridge earthquake region was completed in 1999 with the acquisition of land reflection/refraction data in LARSE II (Los Angeles Region Seismic Experiment, Phase II). These data are combined with onshore-offshore refraction profiling plus multichannel seismic (MCS) data and ocean bottom seismometer (OBS) data collected in 1994 as part of LARSE I. The total data
Eos, Transactions American Geophysical Union, 1997
Scientists from GEOMAR, the U.S. Geological Survey (USGS), and Oregon State University recently c... more Scientists from GEOMAR, the U.S. Geological Survey (USGS), and Oregon State University recently collected seismic reflection and wide-angle seismic data for the continental margin off the Oregon and Washington coasts---a subduction zone that poses a significant earthquake hazard to populated areas of the Pacific Northwest. Geologic findings indicate that great earthquakes (magnitude 8 to 9) have occurred within the Cascadia subduction zone and that an earthquake of this magnitude could some day devastate urban areas of the Pacific Northwest. One such quake may have rocked this region as recently as 300 years ago, and the debate concerning the imminence of the next one continues [Heaton and Kanamori, 1984; Atwater, 1992; Hyndman and Wang, 1993; Wang et al., 1995; Satake et al., 1996]. Potential earthquake source regions along the interplate decollement are unexplored. In fact, the geometry of the downgoing Juan de Fuca plate beneath Oregon and Washington has been poorly understood because of the paucity of shallow (<30 km) earthquakes.
... Gary S. Fuis, David A. Okaya, Robert W. Clayton, William J. Lutter, Trond Ryberg, Thomas M. B... more ... Gary S. Fuis, David A. Okaya, Robert W. Clayton, William J. Lutter, Trond Ryberg, Thomas M. Brocher, Thomas M. Henyey, Mark L. Benthien, Paul M. Davis, James Mori, Rufiis D. Catchings, Uri S. ten Brink, Monica D. Kohler, Kim D. Klitgord, and Robert G. Bohannon ...
In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Wash... more In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Washington was conducted aboard the German R=V Sonne. This cooperative experiment by GEOMAR and the USGS acquired wide-angle reflection and refraction seismic data, using ocean-bottom seismometers (OBS) and hydrophones (OBH), and multichannel seismic reflection (MCS) data. The main goal of this experiment was to investigate the internal structure and associated earthquake hazard of the Cascadia subduction zone and to image the downgoing plate. Coincident MCS and wide-angle profiles along two tracks are presented here. The plate boundary has been imaged precisely beneath the wide accretionary wedge close to shore at ca. 13 km depth. Thus, the downgoing plate dips more shallowly than previously assumed. The dip of the plate changes from 2º to 4º at the eastern boundary of the wedge on the northern profile, where approximately 3 km of sediment is entering the subduction zone. On the southern profile, where the incoming sedimentary section is about 2.2 km thick, the plate dips about 0.5º to 1.5º near the deformation front and increases to 3.5º further landwards. On both profiles, the deformation of the accretionary wedge has produced six ridges on the seafloor, three of which represent active faulting, as indicated by growth folding. The ridges are bordered by landward verging faults which reach as deep as the top of the oceanic basement. Thus the entire incoming sediment package is being accreted. At least two phases of accretion are evident, and the rocks of the older accretionary phase(s) forms the backstop for the younger phase, which started around 1.5 Ma ago. This documents that the 30 to 50 km wide frontal part of the accretionary wedge, which is characterized by landward vergent thrusts, is a Pleistocene feature which was formed in response to the high input of sediment building the fans during glacial periods. Velocities increase quite rapidly within the wedge, both landward and downward. At the toe of the deformation front, velocities are higher than 4.0 km=s, indicating extensive dewatering of deep, oceanic sediment. Further landward, considerable velocity variation is found, which indicates major breaks throughout the accretionary history.
... A curvilinear surficial trace Page 4. 336 ten Brink and Ben-Avraham: Anatomy of the DeadSea P... more ... A curvilinear surficial trace Page 4. 336 ten Brink and Ben-Avraham: Anatomy of the DeadSea Pull-Apart Basin ш 1Л Щ SSW < ce AMAZIAHU ESCARPMENT I LINE 632 MNE ■-■-LINE 4022 AMAZIAHU BASEMENT FAULT ZONE LINE 596 Fig. ...
Waters from the Atlantic Ocean washed southward across parts of Anegada, 11 east northeast of Pue... more Waters from the Atlantic Ocean washed southward across parts of Anegada, 11 east northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, 12 after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of 13 breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime 14 mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to 15 hundreds of meters perpendicular to a 2 km stretch of Anegada's windward shore. Rem 16 nants of the breached ridges stand 3 m above modern sea level, and ridges seaward of the 17 breaches rise 2.2 3.0 m high. The overwash probably exceeded those heights when cutting 18 the breaches by overtopping and incision of the beach ridges. Much of the sand and shell 19 sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand 20 of the breached ridges. This sand extends as much as 1.5 km to the south of the breached 21 ridges. It tapers southward from a maximum thickness of 40 cm, decreases in estimated 22 mean grain size from medium sand to very fine sand, and contains mud laminae in the 23 south. The sand and shell sheet also contains mollusks cerithid gastropods and the 24 bivalve Anomalocardia and angular limestone granules and pebbles. The mollusk shells 25 and the lime mud cap were probably derived from a marine pond that occupied much of 26 Anegada's interior at the time of overwash. The boulders and cobbles, nearly all composed 27 of limestone, form fields that extend many tens of meters generally southward from 28 limestone outcrops as much as 0.8 km from the nearest shore. Soon after the inferred 29 overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats 30 and evaporite crusts. This environmental change, which has yet to be reversed, required A1 This article is intended for tsunami geology issue of Natural Hazards edited by Ioan Nistor:
... By comparing observations of landslide scarps offshore California to peak seismic acceleratio... more ... By comparing observations of landslide scarps offshore California to peak seismic acceleration from shake maps and equating a catastrophic failure with a displacement of at least 1 m, Lee et al. (2000) derived a ratio of k y /K PSA ≤ 0.15. ...
... David C. Twichell a , Corresponding Author Contact Information , E-mail The Corresponding Aut... more ... David C. Twichell a , Corresponding Author Contact Information , E-mail The Corresponding Author , Jason D. Chaytor b , Uri S. ten Brink a and ... and allowed a more detailed mapping of their spatial extent ([EEZ-SCAN 87, 1991], [Booth and O&amp;#x27;Leary, 1991], [Schlee and Robb ...
Over the last 100,000 years, the U.S. Atlantic continental margin has experienced various types o... more Over the last 100,000 years, the U.S. Atlantic continental margin has experienced various types of mass movements some of which are believed to have taken place at times of low sea level. At one of these times of low sea level a significant trigger caused a major submarine mass movement off the coast of Virginia: the Currituck slide which is believed to have taken place between 24 and 50 ka ago. This slide removed a total volume of about 165 km 3 from this section of the continental slope. The departure zone still shows a very clean surface that dips at 4°and is only covered by a thin veneer of postglacial sediment. Multibeam bathymetric and seismic survey data suggest that this slide took place along three failures surfaces. The morphology of the source area suggests that the sediments were already at least normally consolidated at the time of failure. The slide debris covers an area as much as 55 km wide that extends 180 km from the estimated toe of the original slope. The back analysis of slide initiation indicates that very high pore pressure, a strong earthquake, or both had to be generated to trigger slides on such a low failure plane angle. The shape of the failure plane, the fact that the surface is almost clear of any debris, and the mobility analysis, all support the argument that the slides took place nearly simultaneously. Potential causes for the generation of high pore pressures could be seepage forces from coastal aquifers, delta construction and related pore pressure generation due to the local sediment loading, gas hydrates, and earthquakes. This slide, and its origin, is a spectacular example of the potential threat that submarine mass movements can pose to the US Atlantic coast and underline the need to further assess the potential for the generation of such large slides, like the Grand Banks 1927 landslide of similar volume.
Considerable crustal thickness variations are inferred along Cayman Trough, a slow-spreading ocea... more Considerable crustal thickness variations are inferred along Cayman Trough, a slow-spreading ocean basin in the Caribbean Sea, from modeling of the gravity field. The crust to a distance of 50km from the spreading center is only 2–3km thick in agreement with ...
Regional extension of a brittle overburden and underlying salt causes differential loading that i... more Regional extension of a brittle overburden and underlying salt causes differential loading that is thought to initiate the rise of reactive diapirs below and through regions of thin overburden. We present a modern example of a large salt diapir in the Dead Sea pull-apart basin, the Lisan diapir, which we believe was formed during the Quaternary due to basin transtension and subsidence. Using newly released seismic data that are correlated to several deep wells, we determine the size of the diapir to be 13 £ 10 km, its maximum depth 7.2 km, and its roof 125 m below the surface. From seismic stratigraphy, we infer that the diapir started rising during the early to middle Pleistocene as this section of the basin underwent rapid subsidence and signi®cant extension of the overburden. During the middle to late Pleistocene, the diapir pierced through the extensionally thinned overburden, as indicated by rim synclines, which attest to rapid salt withdrawal from the surrounding regions. Slight positive topography above the diapir and shallow folded horizons indicate that it is still rising intermittently. The smaller Sedom diapir, exposed along the western bounding fault of the basin is presently rising and forms a 200 m-high ridge. Its initiation is explained by localized E±W extension due monoclinal draping over the edge of a rapidly subsiding basin during the early to middle Pleistocene, and its continued rise by lateral squeezing due to continued rotation of the Amazyahu diagonal fault. q
... Many of the Hawaiian volcanoes are separated by 50 + 10 km from each other, suggesting ... mo... more ... Many of the Hawaiian volcanoes are separated by 50 + 10 km from each other, suggesting ... modeling of the travel times provide nearly identical estimates of the total crustal thickness, depth ... traverses the flexural moat south of Oahu (Figure 2). Dashed lines mark possible faults. ...
Recent observations of the deformational features on the Muertos compressive margin together with... more Recent observations of the deformational features on the Muertos compressive margin together with sandbox kinematic and gravity modeling question the hypothesized subduction of the Caribbean plate's interior beneath the eastern Greater Antilles island arc. With the aim of testing such subduction, we carried out a wide-angle seismic transect across the widest part of the Muertos compressive margin (longitude 69°W) in the spring of 2009. Shots were fired along the 200 km transect every 90 seconds from the R/V Hesperides' 3850 cubic inches water-gun array, which, towed at 5 knots, resulted in a shot spacing of ~ 230 m. The seismic signal was recorded by five ocean-bottom seismometers deployed at distance intervals from 30 to 50 km. Adjacent reprocessed reflection seismic lines and previous works provided an initial model of the sediment column and the geometry of upper crustal reflectors. A 2-D forward ray-tracing model of the wide-angle transect outlines the broad-scale crusta...
Eos, Transactions American Geophysical Union, 1999
A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reve... more A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reveal much new information about the earthquake threat to U.S. and Canadian urban areas there. A disastrous earthquake is a very real possibility in the region.The survey, known as the Seismic Hazards Investigation in Puget Sound (SHIPS), engendered close cooperation among geologists, biologists, environmental groups, and
As it is known, tsunamis have various general generating mechanisms associated with earthquakes, ... more As it is known, tsunamis have various general generating mechanisms associated with earthquakes, landslides/slumps and volcanic processes. Active tectonics along the north-eastern Caribbean plate is the principal cause de tsunami in the eastern Greater Antilles islands. In this area, earthquake and tsunami record suggest that the main tsunami sources are large shallow earthquakes (6.5) in submarine areas, which can yield
A crustal transect across the 1994 Northridge earthquake region was completed in 1999 with the ac... more A crustal transect across the 1994 Northridge earthquake region was completed in 1999 with the acquisition of land reflection/refraction data in LARSE II (Los Angeles Region Seismic Experiment, Phase II). These data are combined with onshore-offshore refraction profiling plus multichannel seismic (MCS) data and ocean bottom seismometer (OBS) data collected in 1994 as part of LARSE I. The total data
Eos, Transactions American Geophysical Union, 1997
Scientists from GEOMAR, the U.S. Geological Survey (USGS), and Oregon State University recently c... more Scientists from GEOMAR, the U.S. Geological Survey (USGS), and Oregon State University recently collected seismic reflection and wide-angle seismic data for the continental margin off the Oregon and Washington coasts---a subduction zone that poses a significant earthquake hazard to populated areas of the Pacific Northwest. Geologic findings indicate that great earthquakes (magnitude 8 to 9) have occurred within the Cascadia subduction zone and that an earthquake of this magnitude could some day devastate urban areas of the Pacific Northwest. One such quake may have rocked this region as recently as 300 years ago, and the debate concerning the imminence of the next one continues [Heaton and Kanamori, 1984; Atwater, 1992; Hyndman and Wang, 1993; Wang et al., 1995; Satake et al., 1996]. Potential earthquake source regions along the interplate decollement are unexplored. In fact, the geometry of the downgoing Juan de Fuca plate beneath Oregon and Washington has been poorly understood because of the paucity of shallow (<30 km) earthquakes.
... Gary S. Fuis, David A. Okaya, Robert W. Clayton, William J. Lutter, Trond Ryberg, Thomas M. B... more ... Gary S. Fuis, David A. Okaya, Robert W. Clayton, William J. Lutter, Trond Ryberg, Thomas M. Brocher, Thomas M. Henyey, Mark L. Benthien, Paul M. Davis, James Mori, Rufiis D. Catchings, Uri S. ten Brink, Monica D. Kohler, Kim D. Klitgord, and Robert G. Bohannon ...
In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Wash... more In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Washington was conducted aboard the German R=V Sonne. This cooperative experiment by GEOMAR and the USGS acquired wide-angle reflection and refraction seismic data, using ocean-bottom seismometers (OBS) and hydrophones (OBH), and multichannel seismic reflection (MCS) data. The main goal of this experiment was to investigate the internal structure and associated earthquake hazard of the Cascadia subduction zone and to image the downgoing plate. Coincident MCS and wide-angle profiles along two tracks are presented here. The plate boundary has been imaged precisely beneath the wide accretionary wedge close to shore at ca. 13 km depth. Thus, the downgoing plate dips more shallowly than previously assumed. The dip of the plate changes from 2º to 4º at the eastern boundary of the wedge on the northern profile, where approximately 3 km of sediment is entering the subduction zone. On the southern profile, where the incoming sedimentary section is about 2.2 km thick, the plate dips about 0.5º to 1.5º near the deformation front and increases to 3.5º further landwards. On both profiles, the deformation of the accretionary wedge has produced six ridges on the seafloor, three of which represent active faulting, as indicated by growth folding. The ridges are bordered by landward verging faults which reach as deep as the top of the oceanic basement. Thus the entire incoming sediment package is being accreted. At least two phases of accretion are evident, and the rocks of the older accretionary phase(s) forms the backstop for the younger phase, which started around 1.5 Ma ago. This documents that the 30 to 50 km wide frontal part of the accretionary wedge, which is characterized by landward vergent thrusts, is a Pleistocene feature which was formed in response to the high input of sediment building the fans during glacial periods. Velocities increase quite rapidly within the wedge, both landward and downward. At the toe of the deformation front, velocities are higher than 4.0 km=s, indicating extensive dewatering of deep, oceanic sediment. Further landward, considerable velocity variation is found, which indicates major breaks throughout the accretionary history.
... A curvilinear surficial trace Page 4. 336 ten Brink and Ben-Avraham: Anatomy of the DeadSea P... more ... A curvilinear surficial trace Page 4. 336 ten Brink and Ben-Avraham: Anatomy of the DeadSea Pull-Apart Basin ш 1Л Щ SSW < ce AMAZIAHU ESCARPMENT I LINE 632 MNE ■-■-LINE 4022 AMAZIAHU BASEMENT FAULT ZONE LINE 596 Fig. ...
Waters from the Atlantic Ocean washed southward across parts of Anegada, 11 east northeast of Pue... more Waters from the Atlantic Ocean washed southward across parts of Anegada, 11 east northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, 12 after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of 13 breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime 14 mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to 15 hundreds of meters perpendicular to a 2 km stretch of Anegada's windward shore. Rem 16 nants of the breached ridges stand 3 m above modern sea level, and ridges seaward of the 17 breaches rise 2.2 3.0 m high. The overwash probably exceeded those heights when cutting 18 the breaches by overtopping and incision of the beach ridges. Much of the sand and shell 19 sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand 20 of the breached ridges. This sand extends as much as 1.5 km to the south of the breached 21 ridges. It tapers southward from a maximum thickness of 40 cm, decreases in estimated 22 mean grain size from medium sand to very fine sand, and contains mud laminae in the 23 south. The sand and shell sheet also contains mollusks cerithid gastropods and the 24 bivalve Anomalocardia and angular limestone granules and pebbles. The mollusk shells 25 and the lime mud cap were probably derived from a marine pond that occupied much of 26 Anegada's interior at the time of overwash. The boulders and cobbles, nearly all composed 27 of limestone, form fields that extend many tens of meters generally southward from 28 limestone outcrops as much as 0.8 km from the nearest shore. Soon after the inferred 29 overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats 30 and evaporite crusts. This environmental change, which has yet to be reversed, required A1 This article is intended for tsunami geology issue of Natural Hazards edited by Ioan Nistor:
... By comparing observations of landslide scarps offshore California to peak seismic acceleratio... more ... By comparing observations of landslide scarps offshore California to peak seismic acceleration from shake maps and equating a catastrophic failure with a displacement of at least 1 m, Lee et al. (2000) derived a ratio of k y /K PSA ≤ 0.15. ...
... David C. Twichell a , Corresponding Author Contact Information , E-mail The Corresponding Aut... more ... David C. Twichell a , Corresponding Author Contact Information , E-mail The Corresponding Author , Jason D. Chaytor b , Uri S. ten Brink a and ... and allowed a more detailed mapping of their spatial extent ([EEZ-SCAN 87, 1991], [Booth and O&amp;#x27;Leary, 1991], [Schlee and Robb ...
Over the last 100,000 years, the U.S. Atlantic continental margin has experienced various types o... more Over the last 100,000 years, the U.S. Atlantic continental margin has experienced various types of mass movements some of which are believed to have taken place at times of low sea level. At one of these times of low sea level a significant trigger caused a major submarine mass movement off the coast of Virginia: the Currituck slide which is believed to have taken place between 24 and 50 ka ago. This slide removed a total volume of about 165 km 3 from this section of the continental slope. The departure zone still shows a very clean surface that dips at 4°and is only covered by a thin veneer of postglacial sediment. Multibeam bathymetric and seismic survey data suggest that this slide took place along three failures surfaces. The morphology of the source area suggests that the sediments were already at least normally consolidated at the time of failure. The slide debris covers an area as much as 55 km wide that extends 180 km from the estimated toe of the original slope. The back analysis of slide initiation indicates that very high pore pressure, a strong earthquake, or both had to be generated to trigger slides on such a low failure plane angle. The shape of the failure plane, the fact that the surface is almost clear of any debris, and the mobility analysis, all support the argument that the slides took place nearly simultaneously. Potential causes for the generation of high pore pressures could be seepage forces from coastal aquifers, delta construction and related pore pressure generation due to the local sediment loading, gas hydrates, and earthquakes. This slide, and its origin, is a spectacular example of the potential threat that submarine mass movements can pose to the US Atlantic coast and underline the need to further assess the potential for the generation of such large slides, like the Grand Banks 1927 landslide of similar volume.
Considerable crustal thickness variations are inferred along Cayman Trough, a slow-spreading ocea... more Considerable crustal thickness variations are inferred along Cayman Trough, a slow-spreading ocean basin in the Caribbean Sea, from modeling of the gravity field. The crust to a distance of 50km from the spreading center is only 2–3km thick in agreement with ...
Regional extension of a brittle overburden and underlying salt causes differential loading that i... more Regional extension of a brittle overburden and underlying salt causes differential loading that is thought to initiate the rise of reactive diapirs below and through regions of thin overburden. We present a modern example of a large salt diapir in the Dead Sea pull-apart basin, the Lisan diapir, which we believe was formed during the Quaternary due to basin transtension and subsidence. Using newly released seismic data that are correlated to several deep wells, we determine the size of the diapir to be 13 £ 10 km, its maximum depth 7.2 km, and its roof 125 m below the surface. From seismic stratigraphy, we infer that the diapir started rising during the early to middle Pleistocene as this section of the basin underwent rapid subsidence and signi®cant extension of the overburden. During the middle to late Pleistocene, the diapir pierced through the extensionally thinned overburden, as indicated by rim synclines, which attest to rapid salt withdrawal from the surrounding regions. Slight positive topography above the diapir and shallow folded horizons indicate that it is still rising intermittently. The smaller Sedom diapir, exposed along the western bounding fault of the basin is presently rising and forms a 200 m-high ridge. Its initiation is explained by localized E±W extension due monoclinal draping over the edge of a rapidly subsiding basin during the early to middle Pleistocene, and its continued rise by lateral squeezing due to continued rotation of the Amazyahu diagonal fault. q
... Many of the Hawaiian volcanoes are separated by 50 + 10 km from each other, suggesting ... mo... more ... Many of the Hawaiian volcanoes are separated by 50 + 10 km from each other, suggesting ... modeling of the travel times provide nearly identical estimates of the total crustal thickness, depth ... traverses the flexural moat south of Oahu (Figure 2). Dashed lines mark possible faults. ...
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