[1] The two major faults in the Eltanin Fracture Zone are the Heezen Fault and the Tharp Fault. 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. Exploring Data Coaching Activity: Longshore C, SmartFigure: Geostrophic current and western. 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). Sykes & Menke (2006) calculated maximum-likelihood estimates of COV that were 0.3 or smaller for a number of large-to-great earthquakes that ruptured nearly the same segments of strike-slip and subduction zone faults. None of the five is reasonably attributed to a small spreading segment along either of those two transforms. Watts et al. A.B. 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. Ekstram Other short spreading centres may exist along the Tharp and other parts of the Heezen transforms. J.H. For the Eltanin events, this bias is unlikely to be larger than 15 per cent, even for the events with the deepest calculated centroids. Which two plates create the Eltanin Fracture Zone? For the period 19902009, we rejected only one event, which occurred on 2001 August 6. Abstract. The efforts that we made, which are described in Appendix A, resulted in a number of additional solutions, especially for the period 1976-1991 and for Mw 5.4-6.0 (see Fig. In those circumstances the use of longer period Rayleigh and Love waves, as in the CMT methodology, can lead to those events being identified confidently as earthquakes. Molnar McGuire Table S1 in the Supporting Information lists the formal uncertainties of the revised centroid locations. Mw determined in this study compared with the surface wave magnitude Ms as computed by either ISC or PDE for periods between about 17 and 22 s. Mw is determined at longer periods. Cumulative moment release along that segment is displayed in Fig. 2006). The horizontal axis is parallel to computed transform directions; the vertical is perpendicular to it. The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. 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. Our results indicate considerable variation in moment release and hence in fault coupling along the strike of the three Eltanin transforms. (2009). 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. 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. what makes muscle tissue different from other tissues? L.R. If the anomalous trend is real, having one group of events (east or west) off the primary transform then almost becomes a necessary interpretation. Woodhouse SEANOE. Stewart & Okal (1983) concluded that earthquakes along the Eltanin zone from 1920 to 1981 accounted for less than 10 per cent of the slip predicted by kinematic models of plate motion and cooling. Earthquakes of Mw 6.2-6.4 have occurred repeatedly (Fig. This is not surprising since all stations are at large teleseismic distances. We used a 97-km length of the Hollister that includes all large shocks (Fig. 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. 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. Ekstram 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister (Fig. Ekstram Extending the work of Stewart & Okal (1983), they again emphasized the dominance of aseismic slip. We calculate downdip widths of seismic coupling of about 5 km for four strongly coupled segments from observed moment rates and lengths along strike assuming earthquake activity accounts for the entire plate motion. Wolfe M. Tromp VanDeMark (2006) analysed the relative locations of earthquakes of moderate magnitude along oceanic transform faults with a double-difference method using Rayleigh waves of periods between 30 and 80 s. He used 92 events along the Eltanin transform faults from 1980 to early 2006, about half of the number we analysed. Note exaggerated scale in transform-perpendicular direction. I.A. D.K. Our distributions of earthquakes do not fit other thermal models that we have examined. F. Menard T. . Hence, a variety of rupture behaviours, repeat times and maximum observed magnitudes is associated with the active parts of the three transforms. The red series in Fig. Johanson 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. We report the unique occurren 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). -Different segments of the mid-ocean ridge system spreading at different rates. Lonsdale (1994) concludes that a zone of extension north of the Heezen transform developed following a Pliocene change in relative plate motion. Our new catalogue can be used in testing computer simulations of earthquake recurrence. (Ages of chrons are from Gee & Kent 2007). The ridge segments and transform faults of the East Pacific Rise and Pacific-Antarctic ridge are the sites of the fastest rates of the seafloor spreading and relative plate motion in the world. It is one the the major earthquake zones in (1993) attribute it to one of those small spreading centres. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. We did not use the ISC catalogue for events after 1999. Similarly, earthquake recurrence is more difficult to examine for other long oceanic transform faults, such as those in the equatorial Atlantic, that have considerably smaller long-term slip rates. 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. D.F. 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. . If those segments are not fully coupled, our calculations of downdip width, of course, are minimum estimates. Although magmatism was more or less continuous on the ridge during 28-60 Ma, it probably occurred on crust . H.W. 4065 km S of Avarua, Cook Islands / pop: 13,373 / local time: 16:34:59.2 2016-05-02 G. Thermal models with constant and variable mineral physics properties are formally analyzed for fits against recently filtered databases for heat flow and topography. 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 3292km (2046mi) WSW of Puerto Natales, Chile S. Carbotte kindly computed the bathymetric map in Fig. Two 20-km segments of the Hollister transform (Figs 3 and 6) are the sites of several earthquakes of Mw= 5.9 whereas only single shocks of that size are found along its western half. The shaded area is the "Hollister region" whose seismicity is detailed in Fig. W.B.F. Computed CMT depths in Table S1 in the Supporting Information range from 12 to 26 km, with 12 being the smallest constrained depth. Bohnenstiehl They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. The zone is in the South Pacific, southwest of Easter Island, between 56 S, 145 W and 54.5 S, 118.5 W. The Dead Sea fault zone is located on a Transform boundary. . 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. 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. -Linear spreading on Earth's curved surface. Seamount chains in the Pacific basin tend to be aligned northwesterly, and several chains are intimately associated with fracture zones; the Eltanin Fracture Zone in the southwestern Pacific is an example. We used a box from 54S to 58S and 140W to 120W to identify earthquakes that might be located on the Eltanin transform system. We chose one of the Eltanin earthquake of (2009 May 7, Mw= 5.6) for which the CMT centroid depth is 25.7 km, and calculated the CMT at various fixed depths, inverting as usual for all the other parameters. 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? 7; several were the sites of two or three earthquakes of Mw > 6.15. 4). These results suggest that asperities responsible for earthquake release at the Mw > 6 levels vary in size along strike but not much in downdip width. At 14.5W the trough reaches a maximum depth of 2895 fm (5470 m). Cumulative seismic moment release 1971 to 2010 along two segments of Tharp transform as indicated in Fig. 2). Their remoteness and rough seas, however, puts a premium on studying them at large distances using seismic waves and various satellite technologies. Farther west activity decreases to a maximum of Mw 5.9-6.1 between +30 and +100 km along the fault and then again to a maximum of Mw 5.6-5.8 between +10 and 30 km. Ryan . Examine the figure above. Those P waves left hypocentres close to the intersection of the two nodal planes (B-axis) where their amplitude is very small. [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. It and some other segments of the three Eltanin transforms appear to be well coupled seismically. 1). Behn For the larger and more complex 2001 earthquake the rupture initiation depth is 8.9 km, and the centroid depth, taking into account the propagation of the point source in the direction of the directivity vector, is approximately 11 km, about 7 km below the ocean floor. [5], The hydrothermal vents of the MAR support many life forms. . [3], Series of faults that offset the Pacific-Antarctic Ridge. The Atlantis Fracture Zone (30 N) is one of the smallest transform faults along the Mid-Atlantic Ridge with a spatial offset of 70 km and an age offset of ~ 6 Ma. L.M. His events along what we identify as a well-coupled zone between 29 and 59 km in Fig. Our calculations for all events have the advantage of having been corrected for lateral heterogeneity with the same model. From 1995-2003, Eltanin fracture zone was used with Antarctic Ocean and/or Pacific Ocean. Seafloor magnetic anomalies suggest formation. 6. 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. Broader Terms: East Pacific Pacific Ocean South Pacific Southeast Pacific "zone of fracture" in Chinese : , ; ; ,; ; "fracture system" in Chinese : ; "amsterdam fracture zone" in Chinese : We find that one isolated asperity along the Heezen transform ruptures about every 4.0 1.0 yr. 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. Specifically, in the study of the Eltanin earthquakes, we have obtained depths ranging from the shallowest used in the CMT algorithm (12 km) to 26 km. The zone is in the South . 3) along the eastern part of the Heezen transform between +100 and +200 km (Fig. 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. E.A. Fishing enthusiasts interested in fishing near or at Eltanin Fracture Zone System should print out the Google map and take it with them on their . [3], The Romanche Fracture Zone offsets the Mid-Atlantic ridge by 900km (560mi), making it the largest equatorial fracture zone in the Atlantic. It is the only example of a very short time interval between large shocks along segments of the Eltanin transforms. The island is very long and narrow. This attests to the very thin lithosphere at fast spreading ridges. trench to the Eltanin Fracture Zone. Okal When the event of Mw 6.3 on 1969 August 18 (Stewart & Okal 1983) is included, the repeat time of the three largest shocks is 19 yr with a COV of 0.37. You can help Wikipedia by expanding it. Bar at upper right on map shows water depths in metres. It is that region where three of the four normal faulting earthquakes in Fig. The fault segment between -665 and -680 km (green symbols in Fig. T.A. -Different segments of the mid-ocean ridge system spreading at different rates. Fracture zone evolution is investigated using dynamic models that allow the fault zones to freely slip. On the basis of serial hydrographic measurements, the Chain Fracture Zone appears to be separated into several deeper sections. Earth Extremities 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 . Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. Mw is systematically higher than mb for strike-slip events along the three transforms, on average about 0.5 units. S1 in the Supporting Information). The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle. Reported values for the ratios KlRb RblSr La/Yb and Sr87 86ISr for fresh material, generally'"hint at a The continuity in smooth trend of the ridge and the Eltanin Fracture Zone suggests some relationship between them. Boettcher 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. Approximate slopes are denoted by dashed lines. Sykes M.S. If so, their repeat time was about 16 yr but is based on only three events. . Distances along the transform are calculated from an arbitrary origin of coordinates at 55.4 S, 125.0 W. 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). Strike-slip mechanism in centre is that for 2007 event. [1] The two major faults in the Eltanin Fracture Zone are the Heezen Fault and the Tharp Fault. That view was strengthen when Menard reviewed the manuscript and provided an unpublished bathymetric map that included more data in the far southeast Pacific. We then examine other segments with fewer but larger earthquakes. Wolfe et al. McGuire Menard Correct Option: O They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. . Phipps Morgan Others related faults include the Vacquier Transform Fault, the Menard Transform Fault, and the Udintsev Fault.[3]. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. As in Fig. Fracture Zone. 4 occurred. The smooth trend of the ridge is NNW-SSE with a trend break at about 37.8S. 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister . west coast of the USA through California. P. Hence, we cannot distinguish between those two models. The five largest shocks have a repeat time of about 8 yr and a COV of 0.43. 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. D.W. T2=42r3/(GM), m3/(kgs2)m ^ { 3 } / \left( k g \cdot s ^ { 2 } \right) Seabeam and SeaMARC II swath-mapping surveys, with ancillary magnetic and gravity profiling, describe the fast-slipping (84-86 mm year1) 380 km-long Heezen transform (56 S) and the 145 km-long Raitt transform (54 S), together with the youngest parts of their rise-flank fracture zones. Gregg 4. plates. Distances in kilometres same as in Fig. 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. 4. The axes are each rotated with respect to the Euler rotation pole of DeMets et al. The relationship between the two events that occurred on the same day with computed CMTs only 5 km apart is unknown. This is in accord with the findings of Stewart & Okal (1983) that the Eltanin system has not broken in great events since 1920 and is unlikely to do so. 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. By chron 28 (63-64 Ma) about 750 km of the present 1000 km offset had accumulated across them. J.K. Unfortunately, the computed depths of earthquakes along the three Eltanin transforms are not accurate enough to ascertain centroid depths or the downdip width of seismic faulting at the several to 20 km level. Arvidsson What is the answer punchline algebra 15.1 why dose a chicken coop have only two doors? Individual ridge segments trend, how- ever, up to a few tens of degrees from the smooth trend. We note that our revised catalogue with its additions of more solutions, especially of Mw 5.5-6.0, is more complete than the existing CMT catalogue. This yielded 84 earthquakes. . A.R. Fig. Behn However, a major offset developed on this transform between 60 and 80 Ma, prior to the oldest dated rocks from the ridge. Where is and what is Eltanin Transform Fault and Fracture Zone. 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. Dotted lines denote approximate locations of ridges. For the four seismically active fault segments in Table 1 we obtain similar downdip widths of seismic faulting of about 5 km assuming coupling at the full plate rate. 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? Argus M. The Udintsev Fracture Zone is a suitable site for a long-term monitoring of the Antarctic Circumpolar Current 1 Introduction The Antarctic Circumpolar Current (ACC) forms a continuous near-zonal band of eastward flow. In this paper we concentrate on these phenomena using earthquakes that have been relocated and reanalysed using long-period digital data from global stations for a recent 35-yr period (Fig. 3 and studied separately. Systematic deviations can occur when the Earth structure in the source area deviates significantly from the structure assumed in the calculation of synthetic seismograms, that is, from PREM (Dziewonski & Anderson 1981). 4. (2010) that describes the relative motion of the Pacific and Antarctic plates. This is a consequence of the continuity of displacement eigenfunctions for surface waves across discontinuities, and the dependence of the excitation on these displacements. Haiti is situated on a transform boundary also known as a strike D.R. L.R. R.E. E. W. F. Indeed, jets are observed to pass along both the Udinstev and Eltanin Fracture Zones (Gille 1994; Hughes and Ash 2001). For the period 19761989, we selected for analysis all events in the ISC (International Seismological Centre), PDE (Preliminary Determination of Epicentres of the US Geological Survey) and GCMT catalogues, regardless of magnitude. Richards, W.B.F. As it flows north, it is constrained by numerous obstacles on the seafloor. Four segments of the Tharp transform (Fig. 4. The fast rate of plate motion, maximum size of events and relatively short repeat times make these fault segments a good laboratory for research on quasi-periodic behaviour and earthquake prediction. . We interpret it as indicative that only some parts of the three Eltanin transforms are capable of generating shocks of Mw 6.1-6.4 and that events much larger than 6.4, especially events of Mw > 7, are unlikely to occur. In detailed swath mapping of three ultra fast-moving transforms just to the south of the equator, Searle (1983) found that each consisted of two or more short transforms bounded by very short spreading centres. 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. The seismic history of the Eltanin Fracture Zone on the Pacific-Antarctic Ridge for the years 1920-1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction (less than 10%) of the amount of slip predicted by kinematic models of plate motion. Montesi They also calculated Mw for three earthquakes in 1969, 1971 and 1973; they and Molnar et al. florida a jurassic transform plate boundary. transform faults fracture zones and the kinematics of. The morphology of the Atlantis Fracture Zone is typical of that of slow-slipping transforms. transform fault, in geology and oceanography, a type of fault in which two tectonic plates slide past one another. 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.
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