J.T. None of the five is reasonably attributed to a small spreading segment along either of those two transforms. (2010) that describes the relative motion of the Pacific and Antarctic plates. Our findings are in contrast to the widely stated notion that oceanic transform faults, especially those at fast spreading plate boundaries, are poorly coupled with perhaps the presence of occasional stuck patches or asperities. 7. P. D.K. T. The Eltanin Transform Fault and Fracture Zone is a series of six or seven dextral transform faults along ~800 km of the Pacific-Antarctic Ridge that offset it ~1600 km. The segment between -210 and -241 km consists of a large number of events of Mw > 5.55, one of Mw 6.08, three of 6.15 =Mw= 6.17 and one of Mw 6.3 (Stewart & Okal 1983) on 1973 September 18. "eltanin" in Chinese : "fracture zone" in Chinese : ; ; ; ; ; . Fig. Boettcher This is not surprising since all stations are at large teleseismic distances. Which letter(s) is/are pointing to an inactive fracture zone? Okal & Langenhorst (2000) relocated a number of earthquakes along the three transforms using short-period body waves. We take this along with the distributions of events in time and longitude after 1976 (Fig. F. By chron 28 (63-64 Ma) about 750 km of the present 1000 km offset had accumulated across them. Symbols, axes and origin of coordinates same as Fig. Sykes The point source depth of 10.4 km places the 2007 earthquake 6-7 km below the ocean floor. In discriminating the signals of earthquakes from those of underground nuclear explosions low excitation of Rayleigh waves in the narrow period band used for determining Ms may result in a few earthquakes appearing to be explosions. 2. We propose that the remainder of the plate motion . The mechanism in the GCMT catalogue indicates normal faulting, while the reanalysis resulted in a strike-slip mechanism. [2], The trench has a depth of 7,761m (25,463ft), is 300km (190mi) long and has an average width of 19km (12mi) and allows for a major circulation of deep ocean basin water from the west Atlantic to the east Atlantic basins. Extending the work of Stewart & Okal (1983), they again emphasized the dominance of aseismic slip. Incidences of 20,538 trochanteric and femoral neck fractures in adult Swedish men and women, from a computerized medical information register for all hosp Eltanin has a maritime climate in the transition region between the tundra and subarctic zones (Kppen classification) which is characterised by . Also, there was no discontinuous change in the calculated Mo when the CMT was evaluated above the Moho (which in PREM is at 24.4 km) or below it. Swarms of hydrothermal shrimps reminiscent of those found from northern MAR vent-sites have been found on the northern part of the southern MAR. Table S1 in the Supporting Information lists the formal uncertainties of the revised centroid locations. Dziewonski The centroids of events of larger Mw are found at least 35 km eastwards along the Heezen transform and those to its west are relatively small. The greater number of stations in the last 20 years permitted CMT solutions to be obtained for a large number of smaller earthquakes, some as small as Mw 5.15. Fracture zone evolution is investigated using dynamic models that allow the fault zones to freely slip. In that simple model, earthquakes should extend to greater depths and presumably be larger near the centres of transforms, which is clearly not the case for the Heezen and Tharp faults. L.R. A major purpose of our work is to examine the degree of repeatability (or lack thereof) of major earthquakes along various segments of the three Eltanin transforms. When Sykes showed his results to M. Ewing, the latter arranged with NSF (US National Science Foundation) for the Research Vessel Eltanin to map the region. McGuire (2008) examined 16 pairs of Mw= 5.5 earthquakes that occurred along approximately the same segments of transform faults on the East Pacific Rise to the south and north of the equator. Distances in kilometres same as in Fig. Rupture of two or more nearby asperities in shocks as large as Mw 6.4 can occur but is rare as ascertained from the steep slope of the frequency-magnitude relationship in Fig. As in Fig. T. This transform migration was preceded by a process 2517 Ma during which the Miocene shallow-water platform mentioned above reached sea level as the transverse ridge was first uplifted, then deformed, and finally buried under the sea. In the basin on the eastern side of the MAR the Walvis Ridge blocks the northward passage. For the period 19902009, we rejected only one event, which occurred on 2001 August 6. Seafloor magnetic anomalies suggest formation. This section appears to be separated from the western basin of the Atlantic by a sill of 4500 m (2400 fm) near 17W. The series includes two events of 6.17 and 6.18 and one of less certain Mw of 6.5 (Stewart & Okal 1983) on 1971 April 4 that are much larger than the other three. A transform fault may occur in the portion 1999). (1993) found another normal faulting event just to the south of the Menard transform fault at 49.5 S along the same plate boundary. New Mw corresponds to seismic moment magnitude recomputed for this study. As AABW flows through the Romanche Fracture Zone, salinity and temperature increase significantly. Wolfe et al. The waveforms were edited using the standard Global CMT (GCMT) automated waveform editor, and inverted using the standard Global CMT computer codes using corrections for 3-D earth structure in the calculation of synthetic seismograms (Ekstram . 4. This shock of mb 5.6 in the PDE catalogue occurred only 4 min after the Mw 6.7 normal-faulting event near the Heezen transform, and the waveforms are not sufficiently separated to make a CMT analysis possible. 4). The inversion procedure follows the method of Ekstrm (1989) and leads to estimates of the earthquake focal mechanism, source-time function and point-source depth that are consistent with both the P-wave data and the CMT results. Sea-surface shape by satellite Pelagic shrimps of the Family Oplophoridae (Crustacea Decapoda) from the Pacific sector of the Southern Ocean: USNS Eltanin Cruises 10, 11, 14-16, 19-21, 24 . Cumulative seismic moment release from 1976 to 2010 along a 42-km section of Heezen transform indicated in Fig. The Antarctic-Pacific Plate boundary, while characterized by somewhat slower rates than segments of the East Pacific Rise farther north, contains three nearby transform faults-the Heezen, Tharp and Hollister-that together are about 1000 km long and have been the sites of numerous earthquakes of moment magnitude, Mw, 5-6.4 during the past 50 years. Ekstram C. One 30-42-km-long segment of the Heezen transform that appears to be an isolated well-coupled asperity has ruptured in eight earthquakes of Mw 5.9-6.1 quasi-periodically with a coefficient of variation of 0.26 every 4.0 1.0 yr. Other well-coupled fault segments, which were sites with earthquakes up to Mw 6.39 and fewer events since 1976, have average repeat times of about 7-24 yr. transform fault, in geology and oceanography, a type of fault in which two tectonic plates slide past one another. Ekstram We show events characterized by a predominance of strike-slip faulting that we located since 1976 in red along with the few earthquakes in blue that involved a predominance of normal faulting. Bar at upper right on map shows water depths in metres. Bohnenstiehl et al. 7 is not unreasonable for single events of Mw 5.9-6.1. We refer to the magnitudes derived from those moment tensors as either new or recomputed Mws. Elevation map for localities Click for legend, zoom in for elevation lines Routing error m , | Map style: OpenTopoMap ( CC-BY-SA) The average of the three intervals since 1967 is 12.8 yr with a COV of 0.36. In contrast, normal-faulting events of Mw 5-6.5 are common along slower spreading ridges such as those in the Atlantic. Several of those well-coupled segments ruptured quasi-periodically in earthquakes of Mw~5.5-6 and with repeat times shorter than 10 yr. We choose the Eltanin transform faults as another good place to search for these phenomena. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. (1975) obtained strike-slip mechanisms for them and another event in 1967. 4. Our results indicate considerable variation in moment release and hence in fault coupling along the strike of the three Eltanin transforms. The presence of large events just to its west and the variety of Mws, however, suggest that it does not always rupture as a single asperity. The new result is well constrained by the surface wave data, which were not included in the original analysis. 2006). The continuity in smooth trend of the ridge and the Eltanin Fracture Zone suggests some relationship between them. Woodward Richards, W.B.F. In contrast, VanDeMark (2006) used few events, a double-difference methodology and a uniform velocity model for Rayleigh waves in calculating revised earthquake locations along the Eltanin transforms. Surface waves have an advantage for precise locations over body waves since their velocity is much less. [] ( ) "eltanin fracture zone" in Chinese : "eltanin" in Chinese : "fracture zone" in Chinese : ; ; ; ; ; . It is the only example of a very short time interval between large shocks along segments of the Eltanin transforms. This yielded 110 earthquakes for that period. How are fracture zones like the Eltanin created? The data for Mw > 5.9 are fit remarkably well by the slip predictable model of Shimazaki & Nakata (1980) whereby the size of the next earthquake is proportional to the time since the previous event. They find that aftershock zones of nearby pairs of moderate-size earthquakes along fast-moving transforms were separated by small spreading centres. transform plate boundaries learning geology. Available long-period data for events along the three transforms increased from about 15 to 100 global stations as illustrated in Fig. Approximate slopes are denoted by dashed lines. 4. Archived seismicity, satellite altimetry, and older geophysical traverses extend these descriptions . Our locations and those of the ISC based on body waves are located systematically about 25 km south of the transforms as mapped in Fig. Their 1000 km length is greater than that of any other oceanic transforms at fast-spreading plate boundaries. Their remoteness and rough seas, however, puts a premium on studying them at large distances using seismic waves and various satellite technologies. This partitioning of slip likely results from changes during the last few million years in the Euler pole for relative motion between the Antarctic and Pacific plates. Since the length along strike, L, was not determined for individual earthquakes, for the calculations later we took a length of 105 km for the entire eastern end of the Heezen transform, which includes several segments that have ruptured in large shocks (Fig. Louisville chain has been related to the Eltanin fracture zone in several models (Hayes and Ewing, 1971;Larson and Chase, 1972;Watts et al., 1988). 5 and the bathymetric expression of it in Fig. GE was partially supported by NSF grant EAR-09-24694. Log of cumulative number of earthquakes per 20 yr larger than a given Mw as a function of Mw. The zone is in the South . Since the 40-km section of the Tharp (Fig. The Eltanin Fault System(Eltanin Fracture Zone) is a series of six or seven dextral transform faults that offset the Pacific-Antarctic Ridge, a spreading zone between the Pacific Plateand the Antarctic Plate. Explanation: Fracture zones are characterised as structural line View the full answer Transcribed image text: How are fracture zones like the Eltanin created? Clearly, a gradient in the maximum size of earthquakes and seismic coupling occurs between the eastern and western ends of the Heezen transform. Their poorly determined repeat times range from 13 to 24 yr. [2] However, the total offset is about 1600km. The repeat times of those largest events are longer but uncertain since they are based on few earthquakes. Wilson 7 are the best fit to that model. According to the normal scenario for the opening of the South Atlantic, it is spreading at a rate of 1.75 cm/year (0.69 in/year) and began forming about 50 Ma. Use the facts stated above when they apply. 5) are characterized by shocks of Mw= 5.9 but about half of its length is not. Menke McGuire (2008) also found that 1-d aftershock zones extended 30-50 km along strike for Mw~ 6 main shocks for transforms of the East Pacific Rise near the equator. Wilson (1965) utilized the observation that earthquakes along the Eltanin fracture zone were confined to the zone between two offset ridge crests in formulating his hypothesis of transform faulting. We thank S. Carbotte and C. Scholz of Lamont and journal reviewers J. McGuire and C. Laederach for critically examining the manuscript and for valuable suggestions and P.G. Eltanin fracture zone Scope Notes: SE Pacific. R.E. (1993) for two other normal faulting earthquakes off the Eltanin transforms. The Eltanin Fault System (Eltanin Fracture Zone) is a series of six or seven dextral transform faults that offset the Pacific-Antarctic Ridge, a spreading zone between the Pacific Plate and the Antarctic Plate.The affected zone of the Pacific-Antarctic Ridge is about 800 km long, between 56 S, 145 W and 54.5 S, 118.5 W, southwest of Easter Island, and about as far as one can get from . E.A. Locations of earthquakes with CMT solutions (red) characterized by a predominance of strike-slip faulting along the Heezen, Tharp and Hollister transform faults of the Eltanin system from 1976 to 2010. For the Eltanin events, this bias is unlikely to be larger than 15 per cent, even for the events with the deepest calculated centroids. Wolfe Our determinations of Mw typically use observations at more stations than those of Ms. Those for Mw also use Love and Rayleigh waves. [6] (1993) obtained two normal-faulting mechanisms and computed depths of faulting from waveform matching. J. 2006-01-01. Duncan One exception to this general observation is the earthquake on 2000 October 4. His results support the idea that events along that segment break a single isolated asperity. . M. - 4:5, using intermediate-period surface waves, Thermal structure of oceanic transform faults, Scaling relations for seismic cycles on mid-ocean ridge transform faults, Aftershock sequences in the mid-ocean ridge environment: an analysis using hydroacoustic data, Determination of earthquake source parameters from waveform data for studies of global and regional seismicity, A very broad band inversion method for the recovery of earthquake source parameters, Global detection and location of seismic sources using surface waves, Measurements and global models of surface wave propagation, Global seismicity of 2003: centroid-moment-tensor solutions for 1087 earthquakes, Source of oceanic magnetic anomalies and geomagnetic polarity time scale, Spreading rate dependence of gravity anomalies along oceanic transform faults, Co-seismic and postseismic slip of the 2004 Parkfield earthquake from space-geodetic data, Structural geomorphology of the Eltanin fault system and adjacent transform faults of the Pacific-Antarctic plate boundary, Seismic cycles and earthquake predictability on east Pacific rise transform faults, Foreshock sequences and short-term earthquake predictability on east Pacific rise transform faults, Magnetic anomalies, bathymetry and the tectonic evolution of the South Pacific since the Late Cretaceous, Three-dimensional flow and temperature perturbations due to a transform offset, Seismic properties of the Eltanin transform system, South Pacific, Global multi-resolution topography synthesis, Multiple, closely spaced transform faults in fast-slipping fracture zones, The effects of temperature and pressure-dependent viscosity on three-dimensional passive flow of the mantle beneath a ridge-transform system, Time-predictable recurrence model for large earthquakes, Seismicity and aseismic slip along the Eltanin fracture zone, Repeat times of large earthquakes: implications for earthquake mechanics and long-term prediction, Moderate and large earthquake activity along oceanic transform faults, Origin of the Louisville ridge and its relationship to the Eltanin fracture zone system, A new class of faults and their bearing on continental drift, Oceanic transform earthquakes with unusual mechanism or locations: relation to fault geometry and state of stress in the adjacent lithosphere, The Authors Geophysical Journal International 2011 RAS, Fault identification and reliability evaluation using an SVM model based on 3D seismic data volume, Surface waves at a fluid/double-porosity medium interface, Adjoint-state traveltime tomography for azimuthally anisotropic media in spherical coordinates, Defining the Yangtze-Cathaysia suture zone in south china using ambient noise tomography, Observations and simulations of the meteotsunami generated by the Tonga eruption on 15 January 2022 in the Mediterranean Sea, Volume 234, Issue 1, July 2023 (In Progress), Volume 233, Issue 3, June 2023 (In Progress), Volume 233, Issue 2, May 2023 (In Progress), Volume 233, Issue 1, April 2023 (In Progress), Geomagnetism, Rock Magnetism and Palaeomagnetism, Marine Geosciences and Applied Geophysics, Appendix B: Trade-off between scalarmoment estimates and depths of CMTS, https://doi.org/10.1111/j.1365-246X.2011.05284.x, Earthquake interaction, forecasting, and prediction, Oceanic transform and fracture zone processes, Receive exclusive offers and updates from Oxford Academic, Copyright 2023 The Royal Astronomical Society. The surface wave catalogue (Ekstram 2006) starts in 1990, and the magnitude that is associated with events in that catalogue is usually very close to the Mw obtained in a CMT analysis. Lynn R. Sykes, Gran Ekstrm, Earthquakes along Eltanin transform system, SE Pacific Ocean: fault segments characterized by strong and poor seismic coupling and implications for long-term earthquake prediction, Geophysical Journal International, Volume 188, Issue 2, February 2012, Pages 421434, https://doi.org/10.1111/j.1365-246X.2011.05284.x. S1 in the Supporting Information shows the revised CMT solutions for 186 earthquakes from 1976 to 2009 on the left and those in the online catalogue on the right. "fault" or "fault line". 4 and red symbols in Fig. The smooth trend of the ridge is NNW-SSE with a trend break at about 37.8S. Argus Earthquakes of Mw 6.2-6.4 have occurred repeatedly (Fig. 4065 km S of Avarua, Cook Islands / pop: 13,373 / local time: 16:34:59.2 2016-05-02 Shimazaki His relocations are shown in Figs 4-6 in green. The affected zone of the Pacific-Antarctic Ridge is about 800kmlong, between 56 S, 145 W and 54.5 S, 118.5 W,[1] southwest of Easter Island, and about as far as one can get from land on planet Earth (4852.6S 12323.6W). Examine the figure above. The shaded area is the "Hollister region" whose seismicity is detailed in Fig. 7, however, since it is located just to the east of other large shocks along the Heezen transform. Yellow squares show stations for event of 2007 March 31 of Mw= 6.2; the red hexagons show stations for earthquake of 1983 July 5 of Mw= 6.2. We present a compilation of the seismic properties of the Eltanin Transform Fault (TF) system, compelled by the recent discovery of the Hollister Ridge and the possibility of a change of plate kinematics pattern in the region. H.W. Larson west coast of the USA through California. 5. 4814 km S of Papeete, French Polynesia / pop: 26,357 / local time: 08:09:44.3 2016-08-18, Distances: 3385 km SE of Wellington, New Zealand / pop: 381,900 / local time: 14:34:59.2 2016-05-03 No thrust earthquake mechanisms, however, were found along the Tharp zone. The average displacement per earthquake is 0.32 m assuming full coupling and an average repeat time of 4 yr. Figs 8-10 show cumulative moment release throughout 2010 for seven additional segments of the three Eltanin faults. In detail the distribution of fault segments is likely to be fractal. The North Anatolian Fault is formed along the Anatolian plate Enter the email address you signed up with and we'll email you a reset link. and the Eurasian plate. However, a major offset developed on this transform between 60 and 80 Ma, prior to the oldest dated rocks from the ridge. Our calculations for all events have the advantage of having been corrected for lateral heterogeneity with the same model. The seismic history of the Eltanin Fracture Zone on the Pacific-Antarctic Ridge for the years 1920-81 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction (<10%) of the amount of slip predicted by kinematic models of plate motion. Topographic Map of Eltanin Fracture Zone. Palaeoseismically determined dates for earthquakes along faults of the San Andreas system are uncertain, whereas exact dates are known for the events we examine along the Eltanin transforms. [2] However, the total offset is about 1600km. T.F. 10.17882/59800. A 30- to 42-km segment of the Heezen transform fault between 124.05 and 124.75 W was the site of eight shocks of Mw 5.93-6.07 from 1976 to 2010 (Figs 3 and 4) and possibly an earlier event in 1975. 3) to indicate stationarity of well-coupled and poorly coupled behaviour along transform segments since at least 1969. [8], Coordinates: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}000N 1800W / 0.000N 18.000W / 0.000; -18.000, "Dolomite formation in pelagic limestone and diatomite, Romanche Fracture Zone, Equatorial Atlantic", 10.1175/1520-0485(1998)028<1929:MITRFZ>2.0.CO;2, "Lower Cretaceous to Eocene sedimentary transverse ridge at the Romanche Fracture Zone and the opening of the equatorial Atlantic", "Hydrothermal activity on the southern Mid-Atlantic Ridge: Tectonically- and volcanically-controlled venting at 45S", "Transport of Bottom Water in the Romanche Fracture Zone and the Chain Fracture Zone", 10.1175/1520-0485(1998)028<0779:TOBWIT>2.0.CO;2, "Biodiversity and biogeography of hydrothermal vent species: thirty years of discovery and investigations", https://en.wikipedia.org/w/index.php?title=Romanche_Trench&oldid=1090955796, This page was last edited on 1 June 2022, at 10:32.
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