Graphical user interface for interactive seismic ray tracing

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Eos 86 (2005): 90, doi:10.1029/2005EO090004.RayGUI 2.0 is a new version of RayGUI, a graphical user interface (GUI) to the seismic travel time modeling program of Zelt and Smith [1992]. It represents a significant improvement over the previous version of RayGUI (RayGUI 1.04; Loss et al.[1998a,1998b])

Offshore landslide hazard curves from mapped landslide size distributions

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(4), (2019): 3320-3334, doi:10.1029/2018JB017236.We present a method to calculate landslide hazard curves along offshore margins based on size distributions of submarine landslides. The method utilizes 10 different continental margins that were mapped by high‐resolution multibeam sonar with landslide scar areas measured by a consistent Geographic Information System procedure. Statistical tests of several different probability distribution models indicate that the lognormal model is most appropriate for these siliciclastic environments, consistent with an earlier study of the U.S. Atlantic margin (Chaytor et al., 2009, https://doi.org/10.1016/j.margeo.2008.08.007). Parameter estimation is performed using the maximum likelihood technique, and confidence intervals are determined using likelihood profiles. Pairwise comparison of size distributions for the 10 margins indicates that the U.S. Atlantic and Queen Charlotte margins are different than most other margins. These margins represent end‐members, with the U.S. Atlantic margin having the highest mean scar area and the Queen Charlotte margin the lowest. We demonstrate that empirical, offshore landslide hazard curves can be developed from the landslide size distributions, if the duration of mapped landslide activity is known. This study indicates that the shape parameter of the size distribution is similar among all 10 margins, and thus, the shape of the hazard curves is also similar. Significant differences in hazard curves among the margins are therefore related to differences in mean sizes and, potentially, differences in the duration of landslide activity.The authors gratefully acknowledge the constructive comments of this manuscript by Joshu Mountjoy, Tom Parsons, and anonymous reviewer. We also thank Yehuda Ben Zion for managing this manuscript and the scientists who provided the bathymetry data. Margin and landslide polygon shape files and information on bathymetry data sources are available at GSA Repository item number 2016187.2019-10-0

Current subsidence rates due to compaction of Holocene sediments in southern Louisiana

This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 33 (2006): L11403, doi:10.1029/2006GL026300.Relative contributions of geologic and anthropogenic processes to subsidence of southern Louisiana are vigorously debated. Of these, shallow sediment compaction is often considered dominant, although this has never been directly observed or effectively demonstrated. Quantitative understanding of subsidence is important for predicting relative sea level rise, storm surge flooding due to hurricanes, and for successful wetland restoration. Despite many shallow borings, few appropriate stratigraphic and geotechnical data are available for site-specific calculations. We overcome this by determining present compaction rates from Monte Carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the Holocene of southern Louisiana. This approach generates distributions of present compaction rates that are not expected to exceed 5 mm/yr, but may locally. Locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

Slab tears and intermediate‐depth seismicity

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 4244-4248, doi:10.1002/grl.50830.Active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms, such as triple junctions, acute, and obtuse corners. Well‐documented slab tears that are associated with high rates of intermediate‐depth seismicity are considered here: Gibraltar arc, the southern and northern ends of the Lesser Antilles arc, and the northern end of Tonga trench. Seismicity at each of these locations occurs, at times, in the form of swarms or clusters, and various authors have proposed that each marks an active locus of tear propagation. The swarms and clusters start at the top of the slab below the asthenospheric wedge and extend 30–60 km vertically downward within the slab. We propose that these swarms and clusters are generated by fluid‐related embrittlement of mantle rocks. Focal mechanisms of these swarms generally fit the shear motion that is thought to be associated with the tearing process

Bathymetric terrain model of the Atlantic margin for marine geological investigations.

Bathymetric terrain models of seafloor morphology are an important component of marine geological investigations. Advances in acquisition and processing technologies of bathymetric data have facilitated the creation of high-resolution bathymetric surfaces that approach the resolution of similar surfaces available for onshore investigations. These bathymetric terrain models provide a detailed representation of the Earth’s subaqueous surface and, when combined with other geophysical and geological datasets, allow for interpretation of modern and ancient geological processes. The purpose of the bathymetric terrain model presented in this report is to provide a high-quality bathymetric surface of the Atlantic margin of the United States that can be used to augment current and future marine geological investigations. The input data for this bathymetric terrain model, covering almost 305,000 square kilometers, were acquired by several sources, including the U.S. Geological Survey, the National Oceanic and Atmospheric Administration National Geophysical Data Center and the Ocean Exploration Program, the University of New Hampshire, and the Woods Hole Oceanographic Institution. These data have been edited using hydrographic data processing software to maximize the quality, usability, and cartographic presentation of the combined terrain model

The role of premagmatic rifting in shaping a volcanic continental margin: An example from the Eastern North American Margin

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(11),(2020): e2020JB019576, doi:10.1029/2020JB019576.Both magmatic and tectonic processes contribute to the formation of volcanic continental margins. Such margins are thought to undergo extension across a narrow zone of lithospheric thinning (~100 km). New observations based on existing and reprocessed data from the Eastern North American Margin contradict this hypothesis. With ~64,000 km of 2‐D seismic data tied to 40 wells combined with published refraction, deep reflection, receiver function, and onshore drilling efforts, we quantified along‐strike variations in the distribution of rift structures, magmatism, crustal thickness, and early post‐rift sedimentation under the shelf of Baltimore Canyon Trough (BCT), Long Island Platform, and Georges Bank Basin (GBB). Results indicate that BCT is narrow (80–120 km) with a sharp basement hinge and few rift basins. The seaward dipping reflectors (SDR) there extend ~50 km seaward of the hinge line. In contrast, the GBB is wide (~200 km), has many syn‐rift structures, and the SDR there extend ~200 km seaward of the hinge line. Early post‐rift depocenters at the GBB coincide with thinner crust suggesting “uniform” thinning of the entire lithosphere. Models for the formation of volcanic margins do not explain the wide structure of the GBB. We argue that crustal thinning of the BCT was closely associated with late syn‐rift magmatism, whereas the broad thinning of the GBB segment predated magmatism. Correlation of these variations to crustal terranes of different compositions suggests that the inherited rheology determined the premagmatic response of the lithosphere to extension.Financial support was provided by the U.S. Department of Energy Award DE‐FE‐0026087 to Battelle Memorial Institute under the “Mid‐Atlantic U.S. Offshore Carbon Storage Resource Assessment” Project.2021-04-1

Reply to a comment by Carol S. Prentice, Paul Mann, and Luis R. Peña on: “Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region” by U. ten Brink et al.

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 1606–1608, doi:10.1002/jgrb.50147.2013-10-1

The nature of the crust under Cayman Trough from gravity

This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 19 (2002): 971-987, doi:10.1016/S0264-8172(02)00132-0.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 50 km from the spreading center is only 2–3 km thick in agreement with dredge and dive results. Crustal thickness increases to ∼5.5 km at distances between 100 and 430 km west of the spreading center and to 3.5–6 km at distances between 60 and 370 km east of the spreading center. The increase in thickness is interpreted to represent serpentinization of the uppermost mantle lithosphere, rather than a true increase in the volume of accreted ocean crust. Serpentinized peridotite rocks have indeed been dredged from the base of escarpments of oceanic crust rocks in Cayman Trough. Laboratory-measured density and P-wave speed of peridotite with 40–50% serpentine are similar to the observed speed in published refraction results and to the inferred density from the model. Crustal thickness gradually increases to 7–8 km at the far ends of the trough partially in areas where sea floor magnetic anomalies were identified. Basement depth becomes gradually shallower starting 250 km west of the rise and 340 km east of the rise, in contrast to the predicted trend of increasing depth to basement from cooling models of the oceanic lithosphere. The gradual increase in apparent crustal thickness and the shallowing trend of basement depth are interpreted to indicate that the deep distal parts of Cayman Trough are underlain by highly attenuated crust, not by a continuously accreted oceanic crust.DFC was partly supported by NSF grant EAR-92-19796

Size distribution of submarine landslides and its implication to tsunami hazard in Puerto Rico

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L11307, doi:10.1029/2006GL026125.We have established for the first time a size frequency distribution for carbonate submarine slope failures. Using detailed bathymetry along the northern edge of the carbonate platform north of Puerto Rico, we show that the cumulative distribution of slope failure volumes follows a power-law distribution. The power-law exponent of this distribution is similar to those for rock falls on land, commensurate with their interpreted failure mode. The carbonate volume distribution and its associated volume-area relationship are significantly different from those for clay-rich debris lobes in the Storegga slide, Norway. Coupling this relationship with tsunami simulations allows an estimate of the maximum tsunami runup and the maximum number of potentially damaging tsunamis from landslides to the north shore of Puerto Rico