Download or read book Investigating Plate Boundaries Through New High Resolution Bathymetry and Seismic Data 2 Case Studies from the Cascadia Subduction Zone and San Andreas Fault written by Jeffrey Watson Beeson and published by . This book was released on 2016 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: Contiential margins on plate boundaries are complex systems with morphologies and characteristics dictated by the interplay of sediment deposition and erosion, tectonic faulting, folding, and strong ground motion generating mass wasting events. With ever increasing advances in high-resolution remote sensing techniques these systems are increasingly becoming illuminated. A ~120 km offshore portion of the northern San Andreas Fault (SAF) between Point Arena and Point Delgada was mapped using closely spaced seismic-reflection profiles, high-resolution multibeam bathymetry and marine magnetics data. This new dataset documents SAF location and continuity, associated tectonic geomorphology, shallow stratigraphy and deformation. Variable deformation patterns in the generally narrow (~1-km-wide) fault zone are largely associated with fault trend, and with transtensional and transpressional fault bends. We divide this unique transtensional portion of the offshore SAF into six sections along and adjacent to the SAF based on fault trend, deformation styles, seismic stratigraphy, and seafloor bathymetry. This southern region of the SAF includes a 10-km-long zone characterized by two active, parallel fault strands in which the SAF is evolving into a straighter orientation via migrating fault releasing and restraining bends. The SAF in the northern region of the survey area passes through two acute fault bends (~9° (right), and ~8° (left)), resulting in both an asymmetric “Lazy Z” sedimentary basin (“Noyo Basin”) and an uplifted rocky shoal (“Tolo Bank”). Noyo Basin subsidence and tilt rates, as well as SAF lateral slip rates, were determined based on seismic-stratigraphic sequences and unconformities correlated with the previous 4 major Quaternary sea-level lowstands. Progressively steeper erosional surfaces record basin tilting of ~0.6° per 100,000 years. Migration of the basin depocenter indicates a lateral slip rate on the San Andreas Fault of 10 to 19 mm/yr for the past 350,000 years. Data collected west of the SAF on the south flank of Cape Mendocino rule out the previously postulated presence of an offshore fault strand that connects the SAF with the Mendocino Triple Junction. Instead, the SAF passes on land at Point Delgada, where the SAF plate boundary transitions to the Kings Range thrust. Utilizing new high resolution multibeam bathymetric data, chirp sub-bottom and multichannel seismic reflection profiles, we identify and describe submarine channels, submarine landslides, and three “new” erosional features on the toe of the Cascadia accretionary wedge near Willapa Canyon, offshore Washington, USA. Bathymetric data was compiled from the Cascadia Open-Access Seismic Transects (COAST) cruise and from the site survey cruise for the Cascadia Initiative. This new high-resolution dataset has illuminated geomorphic features that suggest this section of the margin underwent radical erosion in the latest-Pleistocene. Three “new” and peculiar features were imaged that superficially resemble slope failures of the frontal thrust, but are distinguished from such failures by 1) incision of the crest of the frontal thrust and anticlinal ridge, and piggyback basin; 2) they have floors below the level of the abyssal plain, and have excavated deeply into the frontal anticline 3) The features are connected to the main Willapa Channel by inactive paleo channels. The features were likely formed during the latest Pleistocene based on post event deposition, cross-cutting by the modern Juan de Fuca and Willapa Channel levees, and post- event slip on the frontal thrust of the Cascadia accretionary prism. Based on morphology, dissimilarity with other submarine features on the Cascadia and other margins, and available age constraints, we infer that these features were most likely formed by massive turbidity currents associated with the glacial lake outpourings in the Pacific Northwest known as the Missoula floods.
Download or read book Paleoseismic Investigations of the Northern San Andreas Fault at the Vedanta Site Marin County California written by Nelson Timothy Hall and published by . This book was released on 1994 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Living on an Active Earth written by National Research Council and published by National Academies Press. This book was released on 2003-09-22 with total page 431 pages. Available in PDF, EPUB and Kindle. Book excerpt: The destructive force of earthquakes has stimulated human inquiry since ancient times, yet the scientific study of earthquakes is a surprisingly recent endeavor. Instrumental recordings of earthquakes were not made until the second half of the 19th century, and the primary mechanism for generating seismic waves was not identified until the beginning of the 20th century. From this recent start, a range of laboratory, field, and theoretical investigations have developed into a vigorous new discipline: the science of earthquakes. As a basic science, it provides a comprehensive understanding of earthquake behavior and related phenomena in the Earth and other terrestrial planets. As an applied science, it provides a knowledge base of great practical value for a global society whose infrastructure is built on the Earth's active crust. This book describes the growth and origins of earthquake science and identifies research and data collection efforts that will strengthen the scientific and social contributions of this exciting new discipline.
Download or read book Subduction Zones Part II written by Larry J. Ruff and published by Birkhäuser. This book was released on 2012-12-06 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Subduction zones consume oceanic lithosphere and are an indispensible part of plate tectonics. Unlike the oceanic lithosphere production system which can be linked as a nearly continuous, albeit sinuous, strand around the earth, subduction zones are a rather dissociated group and are found in several isolated corners of the world. While plate tectonics can predict that subduction zones are required along certain plate boundaries, it does not stipulate how subduction zones initiate and develop. The preservation of newly created oceanic lithosphere and the propensity for spreading centers to fragment continents leaves a wealth of geological informa tion on the initiation and evolution of spreading. On the other hand, the subject of subduction initiation has little observational basis. To find such observations, we need to look at some muddled tectonic regimes. The Macquarie Ridge complex presents a natural laboratory for studies of subduction initiation. 2. Tectonics of the Macquarie Ridge Complex The Macquarie Ridge complex is a complicated physiographic feature that trends approximately north-south between South Island, New Zealand and the Pacific-Antarctica spreading center. This feature consists of a sequence of troughs and ridges, with Macquarie Island as the only exposed expression. The seismically active Macquarie Ridge complex (hereafter: MRC) is crudely continuous with the Tonga-Kermadec-New Zealand seismic activity. The basic physiographic features and seismicity of the MRC are shown in Figure I. The earthquake epicenters generally cluster about the bathymetric expression of the MRC.
Download or read book Plate Boundary Deformation of the Pacific Plate written by Beate Leitner and published by . This book was released on 1999 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two examples of Pacific rim plate boundary deformation are presented. In the first part of the thesis crustal models are derived for the northwestern part of the Vizcaino block in California using marine seismic and gravity data collected by the Mendocino Triple Junction Seismic Experiment. A northwest-southeast trending kink in the Moho is imaged and interpreted to have formed under compression by reactivation of preexisting thrust faults in the paleoaccretionary prism at the seaward margin of the Vizcaino block. The study suggests that the deformation resulted from mainly north-south compression between the Pacific-Juan de Fuca plates across the Mendocino transform fault and predates late Pliocene Pacific-North America plate convergence. In the second part, 195 earthquakes recorded during the duration of the Southern Alps Passive Seismic Experiment (SAPSE) are analysed. Precise earthquake locations and focal mechanisms provide unprecedented detail of the seismotectonics in the central South Island. The short term (6 month) SAPSE seismicity is compared with long term (8 years) seismicity recorded by the New Zealand National Seismic network and the Lake Pukaki network. The seismicity rate of the Alpine fault is low, but comparable to locked sections of the San Andreas fault, with large earthquakes expected. Changes of the depth of the seismogenic zone, generally uniform at about 10-12 km, occur only localised over distances smaller than 30 km, suggesting that thermal perturbations must be of similar scale. This implies that the thermal effects of the uplift of the Southern Alps do not change the seismogenic depth significantly and are not in accordance with most of the present thermal models. Both the Hope and Porters Pass fault zones are seismically active and deformation is accommodated near the fault zones and in the adjacent crust. North of Mt Cook, a triangular shaped region along the Alpine fault is characterised by absence of earthquakes. We interpret this as the result of the plate boundary shift from the Alpine fault to the Hope and Porters Pass fault zones. The study region shows distributed deformation in a 60-100 km wide zone on NNE-SSW trending thrust faults and strike-slip mechanisms on transfer faults.
Download or read book Local Tsunami Hazards in the Pacific Northwest from Cascadia Subduction Zone Earthquakes written by Eric L. Geist and published by . This book was released on 2005 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Science Abstracts written by and published by . This book was released on 1992 with total page 1228 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Sea Level Rise for the Coasts of California Oregon and Washington written by National Research Council and published by National Academies Press. This book was released on 2012-12-06 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tide gauges show that global sea level has risen about 7 inches during the 20th century, and recent satellite data show that the rate of sea-level rise is accelerating. As Earth warms, sea levels are rising mainly because ocean water expands as it warms; and water from melting glaciers and ice sheets is flowing into the ocean. Sea-level rise poses enormous risks to the valuable infrastructure, development, and wetlands that line much of the 1,600 mile shoreline of California, Oregon, and Washington. As those states seek to incorporate projections of sea-level rise into coastal planning, they asked the National Research Council to make independent projections of sea-level rise along their coasts for the years 2030, 2050, and 2100, taking into account regional factors that affect sea level. Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future explains that sea level along the U.S. west coast is affected by a number of factors. These include: climate patterns such as the El Niño, effects from the melting of modern and ancient ice sheets, and geologic processes, such as plate tectonics. Regional projections for California, Oregon, and Washington show a sharp distinction at Cape Mendocino in northern California. South of that point, sea-level rise is expected to be very close to global projections. However, projections are lower north of Cape Mendocino because the land is being pushed upward as the ocean plate moves under the continental plate along the Cascadia Subduction Zone. However, an earthquake magnitude 8 or larger, which occurs in the region every few hundred to 1,000 years, would cause the land to drop and sea level to suddenly rise.
Download or read book Crustal Structure of the Cascadia Fore Arc of Washington written by Tom Parsons and published by . This book was released on 2005 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geophysical Investigations in the Nankai Trough and Sumatran Subduction Zones written by Kylara Margaret Martin and published by . This book was released on 2011 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 2004 Sumatra-Andaman and the 2011 Tohoku-Oki earthquakes demonstrate the importance of understanding subduction zone earthquakes and the faults that produce them. Faults that produce earthquakes and/or tsunamis in these systems include plate boundary megathrusts, splay faults (out of sequence thrusts), and strike-slip faults from strain partitioning. Offshore Japan, IODP Exp. 314 collected logging while drilling (LWD) data across several seismically-imaged fault splays in the Nankai Trough accretionary prism. I combine LWD resistivity data with a model of fluid invasion to compare the permeabilities of sands. My results indicate that sands within faulted zones are 2-3 orders of magnitude more permeable than similar undisturbed sands. Therefore fault zones are likely to be fluid conduits within the accretionary wedge. Fluids can affect the physical and chemical properties of the faulted material, increasing pore pressures and effectively lubricating the faults. Fluids play an important role in fault slip, but hazard analysis also requires an understanding of fault geometry and slip direction. Both Japan and Sumatra exhibit strain partitioning, where oblique convergence between tectonic plates is partitioned between the megathrust and strike-slip faults proximal to the arc. Offshore Sumatra, I combine profiles from a 2D seismic survey (SUMUT) with previous bathymetry and active seismic surveys to characterize the West Andaman Fault adjacent to the Aceh forearc Basin. Along this fault I interpret transpressional flower structures that cut older thrust faults. These flower structures indicate that the modern West Andaman Fault is a right lateral strike-slip fault and thus helps to accommodate the translational component of strain in this highly oblique subduction zone. Offshore the Kii Peninsula, Japan, I analyze a trench-parallel depression that forms a notch in the seafloor just landward of the megasplay fault system, along the seaward edge of the forearc Kumano Basin. Using a 12 km wide, 3D seismic volume, I observe vertical faults and faults which dip toward the central axis of the depression, forming apparent flower structures. The along-strike geometry of the vertical faults makes predominantly normal or thrust motion unlikely. I conclude, therefore, that this linear depression is the bathymetric expression of a transtensional fault system. While the obliquity of convergence in the Nankai Trough is small (~15 degrees), this Kumano Basin Edge Fault Zone could be due to partitioning of the plate convergent strain. The location of the West Andaman Fault and KBEFZ within the forearc may be controlled by the rheology contrast between active accretionary wedges and the more stable crust beneath forearc basins.
Download or read book New Insights Into North America Pacific Plate Boundary Deformation from Lake Tahoe Salton Sea and Southern Baja California written by Daniel Stephen Brothers and published by . This book was released on 2009 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: Five studies along the Pacific- North America (PA-NA) plate boundary offer new insights into continental margin processes, the development of the PA-NA tectonic margin and regional earthquake hazards. This research is based on the collection and analysis of several new marine geophysical and geological datasets. Two studies used seismic CHIRP surveys and sediment coring in Fallen Leaf Lake (FLL) and Lake Tahoe to constrain tectonic and geomorphic processes in the lakes, but also the slip-rate and earthquake history along the West Tahoe-Dollar Point Fault. CHIRP profiles image vertically offset and folded strata that record deformation associated with the most recent event (MRE). Radiocarbon dating of organic material extracted from piston cores constrain the age of the MRE to be between 4.1-4.5 k.y. B.P. Offset of Tioga aged glacial deposits yield a slip rate of 0.4-0.8 mm/yr. An ancillary study in FLL determined that submerged, in situ pine trees that date to between 900-1250 AD are related to a medieval megadrought in the Lake Tahoe Basin. The timing and severity of this event match medieval megadroughts observed in the western United States and in Europe. CHIRP profiles acquired in the Salton Sea, California provide new insights into the processes that control pull-apart basin development and earthquake hazards along the southernmost San Andreas Fault. Differential subsidence (>10 mm/yr) in the southern sea suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline. In contrast to previous models, the rapid subsidence and fault architecture observed in the southern part of the sea are consistent with experimental models for pull-apart basins. Geophysical surveys imaged more than 15 ~N15°E oriented faults, some of which have produced up to 10 events in the last 2-3 kyr. Potentially 2 of the last 5 events on the southern San Andreas Fault (SAF) were synchronous with rupture on offshore faults, but it appears that ruptures on three offshore faults are synchronous with Colorado River diversions into the basin. The final study was used coincident wide-angle seismic refraction and multichannel seismic reflection surveys that spanned the width of the of the southern Baja California (BC) Peninsula. The data provide insight into the spatial and temporal evolution of the BC microplate capture by the Pacific Plate. Seismic reflection profiles constrain the upper crustal structure and deformation history along fault zone on the western Baja margin and in the Gulf of California. Stratal divergence in two transtensional basins along the Magdalena Shelf records the onset of extension across the Tosco-Abreojos and Santa Margarita faults. We define an upper bound of 12 Ma on the age of the pre-rift sediments and an age of ~8 Ma for the onset of extension. Tomographic imaging reveals a very heterogeneous upper crust and a narrow, high velocity zone that extends ~40 km east of the paleotrench and is interpreted to be remnant oceanic crust.
Download or read book New Insights on the Structure of the Cascadia Subduction Zone from Amphibious Seismic Data written by Helen A. Janiszewski and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Major findings include that oceanic plate cooling models do not explain the velocities observed beneath the Juan de Fuca plate, that slow velocities in the forearc appear to be more prevalent in areas modeled to have experienced high slip in past Cascadia megathrust earthquakes, and along strike variations in phase velocity reflect variations in arc structure and backarc tectonics.
Download or read book Paleoseismic Investigation of the San Andreas Fault Zone in Portola Valley California written by Robert Harvey Wright and published by . This book was released on 2002 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Holocene Seismicity of the Northern San Andreas Fault Based on Precise Dating of the Turbidite Event Record written by Hans Nelson and published by . This book was released on 2003 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization of Modern and Historical Seismic Tsunamic Events and Their Global Societal Impacts written by Y. Dilek and published by Geological Society of London. This book was released on 2021-06-22 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt: Earthquakes and tsunamis are devastating geohazards with significant societal impacts. Most recent occurrences have shown that their impact on the stability of nations–societies and the world geopolitics is immense, potentially triggering a tipping point for a major downturn in the global economy. This Special Publication presents the most current information on the causes and effects of some of the modern and historical earthquake–tsunami events, and effective practices of risk assessment–disaster management, implemented by various governments, international organizations and intergovernmental agencies. Findings reported here show that the magnitude of human casualties and property loss resulting from earthquakes–tsunamis are highly variable around the globe, and that increased community, national and global resilience is significant to empower societal preparedness for such geohazards. It is clear that all stakeholders, including scientists, policymakers, governments, media and world organizations must work together to disseminate accurate, objective and timely information on geohazards, and to develop effective legislation for risk reduction and realistic hazard mitigation–management measures in our globally connected world of today.
Download or read book Diffuse Deformation Patterns Along the North American Plate Boundary Zone Offshore Western United States written by Jason D. Chaytor and published by . This book was released on 2006 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plate boundaries are commonly regions of complex, diffuse deformation with the motion across the boundary accommodated by numerous structural systems, rather than being narrow, discrete zones of deformation. One such boundary occurs where the North American plate makes contact with Juan de Fuca, Gorda, and Pacific plates along the west coast of the United States, forming a wide zone of deformation which crosses the ocean-continent transition. Two offshore regions associated with this boundary zone, the Gorda plate and California Continental Borderland, have undergone significant deformation in order to accommodate the changing relative tectonic motion across the boundary. The Gorda plate, seaward of the Cascadia Subduction Zone is deforming as a modified, vertically-hinged flexural-slip buckle that utilizes, via-reactivation, the relict spreading-fabric faults and newly-formed leftlateral strike-slip faults that cut the original fabric. In this way, it appears that the Gorda plate, as the youngest and weakest plate in the system, absorbs the motion of the surrounding plates, essentially buffering the strain accumulation in other regions. In southern California, the plate boundary is dominated by the San Andreas transform system, but with deformation distributed over structures within a zone whose width west of the main San Andreas fault exceeds 300 km. While much of this deforming zone is onshore, a significant component is offshore within the California Borderland and Western Transverse Ranges provinces. Deformation related to the growth of the San Andreas fault system within the Borderland has been ongoing since the late Oligocene, resulting in a poly-deformed terrane of distributed deformation, reflecting the shift from subduction to a highly evolved transform system. Two areas within the Borderland illuminate aspects of the regions complex history: the intersection of the Santa Cruz-Catalina Ridge and northern Channel Islands platform which reflect the current transpressional tectonic regime, and Dall Bank within the Outer Borderland which contains evidence of earlier (Oligocene-Miocene) deformational phases.
Download or read book Cascadia written by and published by . This book was released on 1993 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:
