Abstract Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back-arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat-slab subduction, and rapid absolute upper plate motion overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero.
Research Article| November 01, 2004 Book Review: Geology of the American Southwest W. Scott Baldridge Cambridge University Press, 2004. 296 pages. Hardcover: ISBN 0521816394, $70. Softcover: ISBN 0521016665, $24 Walter D. Mooney Walter D. Mooney USGS Menlo Park, California Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2004) 75 (6): 751. https://doi.org/10.1785/gssrl.75.6.751 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Walter D. Mooney; Book Review: Geology of the American Southwest W. Scott Baldridge Cambridge University Press, 2004. 296 pages. Hardcover: ISBN 0521816394, $70. Softcover: ISBN 0521016665, $24. Seismological Research Letters 2004;; 75 (6): 751. doi: https://doi.org/10.1785/gssrl.75.6.751 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietySeismological Research Letters Search Advanced Search In 1846, at the insistence of President James K. Polk, First Lieutenant William H. Emory led a military reconnaissance across the southwestern USA. The journey started in Missouri and ended in San Diego, California. Emory described the dramatic Basin and Range topography thus: “The mountains run from northwest to southeast, and rise abruptly from the plains in long narrow ridges, resembling trap dykes on a grand scale” (cited in A. M. C. Sengor, 2003, Geological Society of America Memoir 196, Boulder, CO, p. 170). Emory's detailed report to the U.S. Congress was published in 1848 and was followed by many... You do not currently have access to this article.
Research Article| January 01, 1987 A geologic interpretation of seismic-refraction results in northeastern California G. S. FUIS; G. S. FUIS 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar J. J. ZUCCA; J. J. ZUCCA 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar W. D. MOONEY; W. D. MOONEY 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar B. MILKEREIT B. MILKEREIT 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information G. S. FUIS 1U.S. Geological Survey, Menlo Park, California 94025 J. J. ZUCCA 1U.S. Geological Survey, Menlo Park, California 94025 W. D. MOONEY 1U.S. Geological Survey, Menlo Park, California 94025 B. MILKEREIT 1U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (1): 53–65. https://doi.org/10.1130/0016-7606(1987)98<53:AGIOSR>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. S. FUIS, J. J. ZUCCA, W. D. MOONEY, B. MILKEREIT; A geologic interpretation of seismic-refraction results in northeastern California. GSA Bulletin 1987;; 98 (1): 53–65. doi: https://doi.org/10.1130/0016-7606(1987)98<53:AGIOSR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In 1981, the U.S. Geological Survey conducted a seismic-refraction experiment in northeastern California designed to study the Klamath Mountains, Cascade Range, Modoc Plateau, and Basin and Range provinces. Key profiles include 135-km-long, north-south lines in the Klamath Mountains and Modoc Plateau provinces and a 260-km-long, east-west line crossing all of the provinces.The seismic-velocity models for the Klamath and Modoc lines are comparatively homogeneous laterally but are quite different from each other. The Klamath model is finely layered from the surface to at least 14-km depth, consisting of a series of high-velocity layers (6.1–6.7 km/s), ranging in thickness from 1 to 4 km, with alternating positive and negative velocity gradients. A layer with an unreversed velocity of 7.0 km/s extends from 14 km to an unknown depth. The Modoc model, in contrast, is relatively thickly layered and has lower velocities than does the Klamath model at all depths down to 25 km. An upper layer, 4.5 km thick, of low-velocity material (2.1–4.4 km/s) overlies a basement with a considerably higher velocity (6.2 km/s). Velocity increases slowly with depth, with a small velocity step (to 6.4 km/s) at 11 km and a 7.0-km/s layer beginning at 25-km depth. Moho is probably 38–45 km deep under the Modoc Plateau, but its depth is unknown under the Klamath Mountains. A combined velocity-density model for the east-west line consists of a western part similar in configuration to the Klamath velocity model, an eastern part similar to the Modoc velocity model, and laterally changing velocity-density structure in between, in the Cascade Range.Beneath its upper layer, the velocity model for the Modoc Plateau is similar to that determined by other researchers for the adjacent Sierra Nevada. The velocity model is unlike those for rift areas, to which the Modoc Plateau has been compared by some authors. We theorize that beneath a veneer of volcanic and sedimentary rocks (the upper layer), the Modoc Plateau is underlain by a basement of granitic and metamorphic rocks that, like rocks in the Sierra Nevada, are the roots of one or more magmatic arcs.The fine layering in the Klamath seismic-velocity model is consistent with the geologic structure of the Klamath Mountains, characterized by imbricate thrusting of oceanic rock layers of various compositions and ages. Independent modeling of aeromagnetic data indicates that the base of the Trinity ultramafic sheet, the second major rock layer down in the structural sequence, corresponds to a velocity step to 6.7 km/s at 7-km depth in our model. The 6.7-km/s layer beneath the Trinity ultramafic sheet apparently corresponds to rocks of the central metamorphic belt, which are mafic schists. Rock units structurally deeper than rocks of the central metamorphic belt can be correlated with velocity layers below the 6.7-km/s layer, but with less certainty.In the model for the east-west line, the region of laterally changing velocity structure beneath the Cascade Range includes a 10-km step down to the east in the top of the 7.0-km/s layer. This region of lateral velocity change we interpret to be a fault, fold, or intrusive contact (or some combination of the three) between the stack of oceanic rock layers that underlie the Klamath Mountains and the buried roots of magmatic arcs inferred to underlie the Modoc Plateau. Magmas forming the modern Cascade Range arc apparently rise through this region. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract We conducted a seismic intensity survey in Ecuador, following the 16 April 2016 Mw 7.8 Pedernales earthquake, to document the level of damage caused by the earthquake. Our modified Mercalli intensities (MMIs) reach a maximum value of VIII along the coast, where single, two, and multistory masonry and concrete designed buildings partially or completely collapsed. The contours of our MMI maps are similar in shape to the contour maps of peak ground acceleration (PGA) and peak ground velocity (PGV). A comparison of our seismic intensities with the recorded PGA and PGV values reveals that our MMI values are lower than predicted by ground-motion intensity conversion equations that are based on shallow crustal earthquakes. The image of the earthquake rupture obtained using teleseismic backprojection at 0.5–2.0 Hz is coincident with the region of maximum MMI, PGA, and PGV values, Thus, rapid calculation of backprojection may be a useful tool for guiding the deployment of emergency response teams following large earthquakes. The most severe damage observed was, primarily, due to a combination of poorly constructed buildings and site conditions.
Research Article| March 01, 1996 Transition from slab to slabless: Results from the 1993 Mendocino triple junction seismic experiment Bruce C. Beaudoin; Bruce C. Beaudoin 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Nicola J. Godfrey; Nicola J. Godfrey 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Simon L. Klemperer; Simon L. Klemperer 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Christof Lendl; Christof Lendl 2Department of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar Anne M. Trehu; Anne M. Trehu 2Department of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar Timothy J. Henstock; Timothy J. Henstock 3Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Search for other works by this author on: GSW Google Scholar Alan Levander; Alan Levander 3Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Search for other works by this author on: GSW Google Scholar James E. Holl; James E. Holl 4Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015 Search for other works by this author on: GSW Google Scholar Anne S. Meltzer; Anne S. Meltzer 4Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015 Search for other works by this author on: GSW Google Scholar James H. Luetger; James H. Luetger 5U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Walter D. Mooney Walter D. Mooney 5U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Geology (1996) 24 (3): 195–199. https://doi.org/10.1130/0091-7613(1996)024<0195:TFSTSR>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bruce C. Beaudoin, Nicola J. Godfrey, Simon L. Klemperer, Christof Lendl, Anne M. Trehu, Timothy J. Henstock, Alan Levander, James E. Holl, Anne S. Meltzer, James H. Luetger, Walter D. Mooney; Transition from slab to slabless: Results from the 1993 Mendocino triple junction seismic experiment. Geology 1996;; 24 (3): 195–199. doi: https://doi.org/10.1130/0091-7613(1996)024<0195:TFSTSR>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Three seismic refraction-reflection profiles, part of the Mendocino triple junction seismic experiment, allow us to compare and contrast crust and upper mantle of the North American margin before and after it is modified by passage of the Mendocino triple junction. Upper crustal velocity models reveal an asymmetric Great Valley basin overlying Sierran or ophiolitic rocks at the latitude of Fort Bragg, California, and overlying Sierran or Klamath rocks near Redding, California. In addition, the upper crustal velocity structure indicates that Franciscan rocks underlie the Klamath terrane east of Eureka, California. The Franciscan complex is, on average, laterally homogeneous and is thickest in the triple junction region. North of the triple junction, the Gorda slab can be traced 150 km inboard from the Cascadia subduction zone. South of the triple junction, strong precritical reflections indicate partial melt and/or metamorphic fluids at the base of the crust or in the upper mantle. Breaks in these reflections are correlated with the Maacama and Bartlett Springs faults, suggesting that these faults extend at least to the mantle. We interpret our data to indicate tectonic thickening of the Franciscan complex in response to passage of the Mendocino triple junction and an associated thinning of these rocks south of the triple junction due to assimilation into melt triggered by upwelling asthenosphere. The region of thickened Franciscan complex overlies a zone of increased scattering, intrinsic attenuation, or both, resulting from mechanical mixing of lithologies and/or partial melt beneath the onshore projection of the Mendocino fracture zone. Our data reveal that we have crossed the southern edge of the Gorda slab and that this edge and/or the overlying North American crust may have fragmented because of the change in stress presented by the edge. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
In February 1978 a seismic deep-refraction profile was recorded by the U.S. Geological Survey along a 1000-km line across the Arabian Shield in western Saudi Arabia. The line begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, leads southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan (Tihamat-Asir), and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, including 19 in the Farasan Islands. Six shot points were used: five on land, with most charges placed below the water table in drill holes, and one at sea, with charges placed on the sea floor and detonated from a ship. Slightly more than 61 metric tons of explosives were used in 19 discrete firings. Seismic energy was recorded by 100 newly-developed portable seismic stations deployed in approximately 200 km-long arrays for each firing. Each station consisted of a standard 2-Hz vertical component geophone coupled to a self-contained analog recording instrument equipped with a magnetic-tape cassette. In this final report, we fully document the field and data-processing procedures and present the final seismogram data set as both a digital magnetic tape and as record sections for each shot point. Record sections include a normalized set of seismograms, reduced at 6 km/s, and a true-amplitude set, reduced at 8 km/s, which have been adjusted for amplifier gain, individual shot size, and distance from the shot point. Appendices give recorder station and shot information, digital data set descriptions, computer program listings, arrival times used in the interpretation, and a bibliography of reports published as a result of this project. We used two-dimensional ray-tracing techniques in the data analysis, and our interpretation is based primarily on horizontally layered models. The Arabian Shield is composed, to first-order, of two layers, each about 20 km thick, with average velocities of 6.3 km/s and 7.0 km/s, respectively. At the western shield margin the crust thins to less than 20 km total thickness, beyond which the Red Sea shelf and coastal plain are interpreted to be underlain by oceanic crust. A major crustal lateral velocity inhomogeneity northeast of Sabhah in the Shammar Tectonic Province is interpreted as the suture zone of two crustal blocks of different composition. Several high-velocity anomalies in the upper crust correlate with mapped gneissic dome structures. Two intra-crustal reflectors at13 km depth are interpreted as the tops of mafic intrusives. The Mohorovicic discontinuity beneath the shield varies from 43 km depth in the northeast with 8.2 km/s mantle velocity to 38 km depth in the southwest with 8.0 km/s mantle velocity. Two velocity discontinuities are identified in the upper mantle, at 59 and 70 km depth. We suggest further work, including refined analyses of the data employing filtering and synthetic seismogram techniques, as well as consideration of attenuation properties. Extension of the seismic refraction profile to the Arabian Gulf and some short profiles perpendicular to the existing profile would be fruitful areas for future field work.
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