L.R. The segment near the eastern end of the Heezen transform between 179 and 200 km (Fig. T.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. Dziewonski The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. McGuire The few involving normal faulting are located up to 40 km on either side of the transforms and involve extension nearly normal to the transforms. If so, their repeat time was about 16 yr but is based on only three events. Series of faults that offset the Pacific-Antarctic Ridge, "Seismicity and Aseismic Slip Along the Eltanin Fracture Zone", "The Pacififi c-Antarctic Ridge between 4115'S and 5245'S: Survey and sampling during the PACANTARCTIC 2 cruise", "Earthquakes along Eltanin transform system, SE Pacific Ocean: fault segments characterized by strong and poor seismic coupling and implications for long-term earthquake prediction", https://en.wikipedia.org/w/index.php?title=Eltanin_Fault_System&oldid=1068451688, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 28 January 2022, at 13:46. . Dziak While off-transform normal-faulting events and short intra-transform spreading centres are reasonably attributed to changes in plate motion, we do not find evidence from earthquake mechanisms along the Eltanin transforms that those faults are leaky' today in the sense proposed by Menard & Atwater (1969). This attests to the very thin lithosphere at fast spreading ridges. 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. Distances in kilometres same as in Fig. . McGuire Surface waves have an advantage for precise locations over body waves since their velocity is much less. 4), to constrain their source depths. G. 2 shows the areal distribution of strike-slip earthquakes Mw > 5.5 as a function of their recomputed magnitude, Mw, in red along the three transform faults of the Eltanin system. How are fracture zones like the Eltanin created? From 1995-2003, Eltanin fracture zone was used with Antarctic Ocean and/or Pacific Ocean. The two largest (Mw 6.7 and 5.9) occurred well to the north of the transform in 2001 and 2007. This is a much smaller difference than might have been anticipated from ratios of body-wave radiation amplitudes or other methods. They proposed that the Eltanin transforms consisted of small, well-separated asperities that rupture in earthquakes. A.B. Data for the reanalysis were collected from all the main global digital networks that have operated since 1976. 7; several were the sites of two or three earthquakes of Mw > 6.15. I cover many earth extremities ranging from Earthquakes, Quake Swarms, Volcanic Activity/Eruptions, CME's Coronal Mass Ejections, Solar Flares, Geomagnetic Storms, Magnetosphere Pressure plus other solar related radiation pulses, Asteroid/Meteorite Threats, Solar System Threats, Landslides, Flooding, Sink Holes, Hurricanes, Typhoons, Storms, Tsunami's, prolonged Snowfall/Ice, Heatwaves, Drought, Nuclear Fallout/Leak, Viruses, Deceases, Epidemics, Dead Mammals/Birds/Animals, Pollution Threat Levels and many more events. Okal [4] (1981), Arvidsson & Ekstrm (1998) and Ekstrm et al. (1997) for the intermediate-period, fundamental-mode surface waves. Enter the email address you signed up with and we'll email you a reset link. Our new catalogue can be used in testing computer simulations of earthquake recurrence. Nearby asperities, as along the eastern part of the Heezen transform, may break either individually or together. E.A. The maximum size of earthquakes along fast spreading ridges themselves is not greater than magnitude 3 (McGuire 2008; M. Tolstoy, personal communication, 2010). (1993) and Lonsdale (1994) describe three short spreading centres with a total length of about 6 km along the seismically quiet part of the Heezen transform between 125.5 and 126 W (Fig. Eltanin fracture zone Scope Notes: SE Pacific. H.W. We also analysed the P waves of the two largest normal-faulting events, those of 2001 and 2007 (Fig. The eastern part of the transverse ridge, however, consists of a thick sequence of stratified material called the Romanche Sedimentary Sequence (RSS). Earthquakes of Mw 6.2-6.4 have occurred repeatedly (Fig. That view comes in large part from assuming that the downdip (vertical) width of seismic faulting extends to about the 600 C isotherm as calculated using simple conductive plate cooling models where temperature at a given location along the transform is taken as the average on its two sides. The repeat times of those largest events are longer but uncertain since they are based on few earthquakes. Subsequent locations of earthquakes and mapping of bathymetry and magnetic anomalies showed that the Eltanin zone consisted of three en echelon transforms (Molnar et al. Nearby ocean bottom seismometers are needed to detect them. Our calculations of moment magnitude Mw are compared with determinations of the short-period magnitude mb in Fig. The feature was then named the Eltanin fracture zone. If we assume that all of the true depths of these earthquakes are shallow, what size error or bias should we expect in estimates of Mo? Sunrise: 06:37AM; Sunset: 05:22PM; Day length: 10h 45m; The local time in Stockholm County is currently the same as the solar time. At faster separating parts of the Pacific-Antarctic boundary, and on most of the rest of the EPR, fracture zone structure is mainly inherited from the variable arrangement of volcanic ridges and tectonic uplifts at the risecrest intersections, rather than from structures formed at the transform valley. Map view of CMT locations of earthquakes along Tharp transform from 1976 to 2010. Antarctic Bottom Water (AABW) flows below the LNADW and reaches down to the seafloor. A.M. Gee The completeness of the CMT data set as a function of time is described later. Moment release over 35 yr per unit length along strike for each of those segments is 3.5 0.7 1014 N m m-1. His relocations along the Heezen transform, with one exception, are more tightly clustered than ours. The along strike dimensions and perhaps the downdip widths of asperities must be small for parts of the three Eltanin faults that have not ruptured in events larger than Mw 5.0-5.5. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. 4). The average repeat time for the eight events of Mw > 5.9 is 4.0 1.0 (1 SD) yr. 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister (Fig. They differ in that hypocentres derived using body waves give the location of rupture initiation whereas CMT solutions give centroid locations and origin times. Boettcher & McGuire (2009) conclude that the largest earthquakes on several fast-spreading transforms do not scale directly with the fault area shallower than their calculated 600 C isotherm. 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. We used a 97-km length of the Hollister that includes all large shocks (Fig. R. . The three sets of large events have a repeat time of 13 yr and a COV of 0.13. For example, if it is known that an earthquake occurred at a depth of 10 km, and the CMT was calculated at 25 km, is there a corresponding bias in the CMT estimate of Mo? The risk of fracturing the proximal femur is high for individuals with metabolic bone disease or with low bone mass associated with advanced age. We have combined shipboard and Seasat altimeter derived data in an intergrated geological and geophysical study of the Louisville Ridge; a 3500kmlong seamount chain extending from the Tonga trench to the Eltanin Fracture Zone. (1993) for two other normal faulting earthquakes off the Eltanin transforms. We determined a CMT solution for it using seven digital stations and obtained a Mw of 6.1, a strike-slip mechanism and a location (red triangle) about 20 km west of the group indicated in Fig. Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. Earthquakes of Mw > 5.55 were included in each computation. Mammericks It moves 8) contains six events of Mw= 5.89 since 1971. 4. florida a jurassic transform plate boundary. Thus, the use of the CMT methodology insured more complete coverage of earthquakes in this very remote area of the Earth. L.M. A.M. Lat: A.M. Bohnenstiehl et al. G. The most recent data show, for example, that the Eltanin fracture zone system in the South Pacific is much longer than previously thought, according to Marsh. Enter your email address to follow this blog and receive notifications of new posts by email. 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. 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. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle. Clearly, a gradient in the maximum size of earthquakes and seismic coupling occurs between the eastern and western ends of the Heezen transform. Arvidsson Reported values for the ratios KlRb RblSr La/Yb and Sr87 86ISr for fresh material, generally'"hint at a A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. W.B.F. Bathymetry from Ryan et al. Three normal-faulting events were found with T-axes nearly perpendicular to the Heezen transform (Fig. J.K. Seafloor magnetic anomalies suggest formation. Their length, relative simplicity, 80 mm yr-1, long-term slip rate and the lack of known shocks of Mw > 7 make them a good laboratory for studying quasi-periodic recurrence of earthquakes on a timescale of years to a few decades. 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister . Wolfe et al. We also used the same 3-D velocity model for our new CMT solutions. Distances in kilometres same as in Fig. Nine earthquakes from 1969 to 1975 are shown at their body wave locations of the International Seismological Centre (ISC). Challenger Fracture Zone. We conclude that strike-slip and normal faulting along the three Eltanin transforms are partitioned so that strike-slip faulting takes place along the transforms themselves and normal faulting occurs nearby but just off the transforms. In relocating earthquakes along the East Pacific Rise and Pacific-Antarctic Ridge, Sykes (1963) found that the pattern of epicentres was offset about 1000 km near 55 S. 3391km (2107mi) WSW of Ushuaia, Argentina Tromp 11 between Mw 5.4 and 6.0 for events from 1991 to 2010. Thermal models with constant and variable mineral physics properties are formally analyzed for fits against recently filtered databases for heat flow and topography. Ekstram They found that between chron 27 (61 Ma) and 34 spreading rates were about twice as high to the north of the two transforms than to their south. 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. [3], Series of faults that offset the Pacific-Antarctic Ridge. 4, between 75 and 125 km). 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. 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. Knowledge gained from them and other oceanic transform faults may aid in understanding the long-term behaviour of transform faults on land and those at subduction zones where large-to-great earthquakes recur with repeat times of 100 yr or more. This technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots. D.W. The transverse ridge separates the present trench from an 800km (500mi)-long aseismic valley where the Romanche transform was located until about 108 Ma. Deep water flow through the trench is from west to east with a rate of 3.6 Sverdrups (million m/s) of 1.57C (34.83F) water. E.A. Tolstoy The Romanche Trench, also called the Romanche Furrow or Romanche Gap, is the third deepest of the major trenches of the Atlantic Ocean, after the Puerto Rico Trench and the South Sandwich Trench. In detail the distribution of fault segments is likely to be fractal. 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. Major differences in seismic coupling along strike are not in accord with common thermal models of plate cooling but instead are attributed to varying degrees of metamorphism, rock type and effective normal stress and possibly to the presence of short intratransform spreading centres. His relocations are shown in Figs 4-6 in green. That Ms was obtained using a single station. What causes the formation of offsets in the mid-ocean ridge system? The existence of three or four plates in the region during those times permitted offset to grow across the Eltanin system (Watts et al. Nevertheless, modelling body waves is difficult for strike-slip earthquakes along the Eltanin transforms because their amplitudes are small at recording stations that necessarily are at very large distances. 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. Extending the work of Stewart & Okal (1983), they again emphasized the dominance of aseismic slip. Examine the figure above. Lamont-Doherty Earth Observatory Contribution 7505. They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. We show in detail, however, that some segments of the three transforms are aseismic at the Mw > 5.4 level whereas others are more strongly coupled. . [1], Lower North Atlantic Deep Water (LNADW) is found around 3,6004,000 metres (11,80013,100ft) below sea level and flows from the Greenland and Norwegian seas; it brings high salinity, oxygen, and freon concentrations towards the equator. 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 solutions, additional methodology and other pertinent data are described more fully in Appendix A and the Supporting Information. How do you say Eltanin Fracture Zone? . The random variations can be considered a consequence of the complicated trade-offs that occur when noisy data are fit with synthetic seismograms that do not capture the full complexity of wave propagation in the Earth. Our work using much greater numbers of stations and earthquakes confirms the general findings of Stewart and Okal about the abundance of aseismic slip and the presence of asperities. Shimazaki 1 for events of Mw 6.2 in 1983 and 2007. 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). The total length of the three en echelon faults is nearly 1000 km; each is characterized by fast long-term rates of displacement of about 80 mm yr-1. 4 are more tightly clustered in map view. stand on one side of it, the other side appears to move to the (2005), McGuire (2008) and Boettcher & McGuire (2009) find that some fault segments are characterized by a predominance of aseismic slip while others are fully coupled. Our determinations of Mw typically use observations at more stations than those of Ms. Those for Mw also use Love and Rayleigh waves. This section appears to be separated from the western basin of the Atlantic by a sill of 4500 m (2400 fm) near 17W. The morphology of the Atlantis Fracture Zone is typical of that of slow-slipping transforms. We choose to use a greater number of stations as time proceeded rather than use a few common stations as he did. M. Lonsdale S. Carbotte (written communication, 2011 July 22) notes, however, that some of the shocks along the eastern end of the Tharp transform might fall within a zone of deformed/rotated seafloor south of the transform that looks quite similar to the zone of deformation north of the Heezen transform described by Lonsdale (1994) and seen in Fig. Individual ridge segments trend, how- ever, up to a few tens of degrees from the smooth trend. . 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. Somewhat smaller estimates of W are obtained using a value of appropriate to the uppermost mantle. Four of them have T-axes nearly perpendicular to those transforms while the smallest of Mw 5.3 in 1982 is oriented about 45 to the Tharp. . H.W. 5 and the bathymetric expression of it in 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 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 . Others related faults include the Vacquier Transform Fault, the Menard Transform Fault, and the Udintsev Fault.[3]. 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. 3). As in Fig. Only the Heezen transform has been surveyed by swath mapping (Lonsdale 1994). J. Their surface wave magnitudes, Ms, are plotted. Cumulative seismic moment release from 1976 to 2010 along a 42-km section of Heezen transform indicated in Fig. For the period 19902009, we rejected only one event, which occurred on 2001 August 6. 6. The four estimates of W in Table 1 range from 3.9 to 6.0 km. Which two plates create the Eltanin Fracture Zone? 4065 km S of Avarua, Cook Islands / pop: 13,373 / local time: 16:34:59.2 2016-05-02 They were generally too small to generate stable CMT results. In this method, the moment tensor and source centroid are estimated by matching observed long-period three-component seismograms to synthetic waveforms calculated using normal-mode summation. . 4. COV = 0 and 1.0 correspond to strict periodicity and random occurrence, respectively. Nevertheless, strike-slip earthquakes along the three transform faults are much more numerous and have together released more seismic moment than the normal-faulting events. 'dextrally' (also known as right-laterally) which means if you Others related faults include the Vacquier Transform Fault, the Menard Transform Fault, and the Udintsev Fault. This completeness can be seen as well by the slope of 1.0 of the LogNMw relationship in Fig. The 40Ar39Ar dating of rocks dredged . The experiment suggests that when the CMT depth is larger than the true depth, the estimated Mo is too high by a small amount. J.S. 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. D.V. Watts 2. Swarms of hydrothermal shrimps reminiscent of those found from northern MAR vent-sites have been found on the northern part of the southern MAR. A Seabeam reconnaissance of the 400 km-long fast-slipping (88 mm yr-1) Heezen transform fault zone and the 55 km-long spreading center that links it to Tharp transform defined and bathymetrically described several types of ridges built by tectonic uplift and volcanic construction. . Is the singer Avant and R Kelly brothers? A.R. . . Wolfe et al. Those P waves left hypocentres close to the intersection of the two nodal planes (B-axis) where their amplitude is very small. Approximate slopes are denoted by dashed lines. These are very small, typically 3-15 km for the earliest events and 1-2 km for earthquakes since 2000. Available long-period data for events along the three transforms increased from about 15 to 100 global stations as illustrated in Fig. Kent For full access to this pdf, sign in to an existing account, or purchase an annual subscription. and the Eurasian plate. The point-source depths are about 10-12 km, which suggests that the earthquakes ruptured faults that cross the M discontinuity. Since CMT locations are not available before 1976, the 10 largest earthquakes from 1969 to 1975 are shown in green at their body-wave locations of the International Seismological Centre (ISC). . Red triangle indicates CMT solution for shock of 1975 April 19. E.A. The 2004 Parkfield earthquake of Mw 6.0 had a rupture length of 20-25 km (Johanson et al. Previously, some epicentral locations in that area were uncertain by as much as 500 km. The segment between -575 and -580 km was the site of only two large earthquakes, Mw 6.22 and 6.24. (1993) and Abercrombie & Ekstrm (2001) clearly include the uppermost oceanic mantle for earthquakes along three slower moving transform faults in the Equatorial Atlantic. . [] ( ) "eltanin fracture zone" in Chinese : "eltanin" in Chinese : "fracture zone" in Chinese : ; ; ; ; ; . E. W. F. (2009). 2. Bathymetric Features 67%. Figs 4-6 depict the three Eltanin transforms in greater detail. plates. of fracture zones in the southern oceans by mavis lynn driscoll b.a., university of california at berkeley, 1981 submitted in partial fulfillment of the requirements for the degree of doctor of philosophy at the massachusetts institute of technology and the woods hole oceanographic institution june 1987 M.D. 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. This is a consequence of the continuity of displacement eigenfunctions for surface waves across discontinuities, and the dependence of the excitation on these displacements. Cumulative seismic moment release for shocks of Mw > 5.55 from 1969 to 2010 along three additional segments of Heezen transform fault as indicated in Fig. . 4706 km S of Papeete, French Polynesia / pop: 26,400 / local time: 01:42:15.1 2017-06-15 The fracture along blocks of crust (tectonic plates) is called a Indeed, jets are observed to pass along both the Udinstev and Eltanin Fracture Zones (Gille 1994; Hughes and Ash 2001). His results support the idea that events along that segment break a single isolated asperity. Four segments of the Tharp transform (Fig. Abstract. 4279 km S of Papeete, French Polynesia / pop: 26,357 / local time: 16:34:59.2 2016-05-02, Distances: 1977km (1228mi) N of Siple, Mount, Antarctica .
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