New Mw corresponds to seismic moment magnitude recomputed for this study. 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. Those P waves left hypocentres close to the intersection of the two nodal planes (B-axis) where their amplitude is very small. Seafloor magnetic anomalies suggest formation. . a generally flat zone extending from the shore to the shelf break continental margin shallow-water areas close to continent abyssal plain flat depositional surfaces that cover extensive portions of the deep-ocean basins The method that used most frequently to investigate sediment and rock layers of the sea floor is: [4] As in Fig. . Red triangle indicates CMT solution for shock of 1975 April 19. Strike-slip faulting with moment magnitudes Mw up to 6.4 characterizes most of these events. 1 for events of Mw 6.2 in 1983 and 2007. C1. fracture zones and transform faults flashcards quizlet. 5. Eltanin Fracture Zone System is located in the Undersea Features Area of the Country of Undersea Features. 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. Which letter is pointing to a transform fault? McGuire A.M. Shen N.N. . (2010) that describes the relative motion of the Pacific and Antarctic plates. Note exaggerated scale in transform-perpendicular direction. Wolfe et al. A single strike-slip event of Mw 5.15 was obtained along a long section of the western part of the Heezen transform between -110 and +10 km. Events in 2010 were determined in the same manner and are listed in the catalogue of the GCMT project at http://www.globalcmt.org. 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. L.R. Only the Heezen transform has been surveyed by swath mapping (Lonsdale 1994). LOUISVILLE RIDGE AND ELTANIN FRACTURE ZONE 3053 west to isolated peaks superimposed on ridge segments in the southeast. The catalogue for the latter period appears to be complete for Mw > 5.4-5.5 whereas the earlier period is not complete for Mw < 6.0. 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. Somewhat smaller estimates of W are obtained using a value of appropriate to the uppermost mantle. Their surface wave magnitudes, Ms, are plotted. Cumulative moment release along that segment is displayed in Fig. Fig. 4 occurred. T.F. From 1995-2003, Eltanin fracture zone was used with Antarctic Ocean and/or Pacific Ocean. It is therefore unlikely that the event selection for 19902009 missed any earthquake with a moment magnitude greater than 5.5. 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. Events of Mw > 5.9 account for 70 per cent of the moment 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. Solid line indicates Mw=Ms. Moment magnitudes are given below each solution. H.W. Smith (2007) and others modelled temperatures in the vicinity of oceanic transform faults at fast moving plate boundaries that differ from those for the earlier simple plate cooling models. To the north of the Eltanin Fracture Zone, a wider compositional diversity seems to occur, including FeTi-basaltsand trachy andesite, than that observed from within and to the south of this fracture zone and on the Chile Rise. Ships have surveyed the active parts of three Eltanin transforms infrequently since they straddle the pole of inaccessibility' at the farthest point on the Earth from inhabited land (Lonsdale 1994). 2. E. W. F. Eltanin is an island located in the South Pacific Ocean, following the contours of the Eltanin Fracture Zone. An up-to-date map of the Antarctic Circumpolar Current (ACC) fronts is constructed from the latest version of mean dynamic topography from satellite altimetry (Park et al., 2019, Observations of the Antarctic Circumpolar Current over the Udintsev Fracture Zone, the narrowest choke point in the . Eltanin has a maritime climate in the transition region between the tundra and subarctic zones (Kppen classification) which is characterised by . Experience has shown that deviations of the CMT centroid depth from the true depth occur both randomly and systematically. T.H. His relocations are shown in Figs 4-6 in green. 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. This section appears to be separated from the western basin of the Atlantic by a sill of 4500 m (2400 fm) near 17W. Dziewonski 4. 8) contains six events of Mw= 5.89 since 1971. If those short spreading centres are very young, they may not have had enough time to become oriented perpendicular to the transform. They are typified by some of the roughest sea conditions and most severe weather on the Earth. Some of our largest events occur within about 25 km of the eastern end of the Heezen and the western end of the Hollister transforms (Figs 4 and 6). 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. Hence, a variety of rupture behaviours, repeat times and maximum observed magnitudes is associated with the active parts of the three transforms. The time-predictable model (not shown), in which the time to the next earthquake is proportional to the size of the preceding large event, also fits the data, though slightly less well. 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. J.H. 7; several were the sites of two or three earthquakes of Mw > 6.15. . Most prominent is an asymmetric transverse ridge, at which abyssal hills adjacent to the fault zone have been . McGuire The precision of epicentral locations in his study was improved considerably by using data from new seismic stations in Antarctica that were installed during the International Geophysical Year, 1957-1958, and computer programs for analysing P and PKP arrival 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. Stewart & Okal (1983) modelled P and reflected body waves for several strike-slip events along the Eltanin system. 7, many of the smaller events are either aftershocks or foreshocks and are considered to be noise for the purposes of assessing the repeat times of the largest earthquakes. 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. You can help Wikipedia by expanding it. et al. W. K. If the anomalous trend is real, having one group of events (east or west) off the primary transform then almost becomes a necessary interpretation. The two largest (Mw 6.7 and 5.9) occurred well to the north of the transform in 2001 and 2007. The red series in Fig. Previously, some epicentral locations in that area were uncertain by as much as 500 km. Argus 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 . Fracture Zones : Mendocino Fracture Zone, Murray Fracture Zone, Molokai Fracture Zone, Clarion Fracture Zone, Clipperton Fracture Zone, Challenger Fracture Zone, Eltanin Fracture Zone, Udintsev Fracture Zone Other Pacific Ocean ocean maps Physiography of the Pacific Ocean Countries and islands of the Pacific Region Menard It seems unlikely that our CMT location errors would change much over the length of the Tharp transform. The average repeat time for the eight events of Mw > 5.9 is 4.0 1.0 (1 SD) yr. 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. 4. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. As it flows north, it is constrained by numerous obstacles on the seafloor. The fault segment between -665 and -680 km (green symbols in Fig. C. Cumulative seismic moment release for shocks of Mw > 5.55 from 1976 to 2010 along two segments of Hollister transform fault as indicated in Fig. . (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. The synthetic waveforms used in the CMT inversion are corrected for lateral heterogeneity using the whole-mantle model of Dziewonski & Woodward (1992) for the body waves and long-period mantle waves, and the phase-velocity maps of Ekstrm et al. McGuire The data since 1969 and those of Stewart & Okal (1983) for events back to 1920 indicate that earthquakes of Mw > 7 have not ruptured very long segments of any of the transforms. Weissel Data for the reanalysis were collected from all the main global digital networks that have operated since 1976. stand on one side of it, the other side appears to move to the The four estimates of W in Table 1 range from 3.9 to 6.0 km. J.J. Phipps Morgan & Forsyth (1988), Shen & Forsyth (1992), Behn (2007), Gregg et al. The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. NASA Technical Reports Server (NTRS) Kyte, Frank T.; Gersonde, Rainer; Kuhn, Gerhard. (1993) attribute it to one of those small spreading centres. We find that one isolated asperity along the Heezen transform ruptures about every 4.0 1.0 yr. The axes are each rotated with respect to the Euler rotation pole of DeMets et al. 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. Bohnenstiehl It is the only example of a very short time interval between large shocks along segments of the Eltanin transforms. However, a major offset developed on this transform between 60 and 80 Ma, prior to the oldest dated rocks from the ridge. 10.17882/59800. Publisher. (1997) for the intermediate-period, fundamental-mode surface waves. At 14.5W the trough reaches a maximum depth of 2895 fm (5470 m). 3 and studied separately. Table S1 in the Supporting Information lists the formal uncertainties of the revised centroid locations. The excitation of the long-period waveforms used in the CMT analysis does not vary rapidly as a function of source depth for shallow-focus earthquakes. 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? T2=42r3/(GM), m3/(kgs2)m ^ { 3 } / \left( k g \cdot s ^ { 2 } \right) . right. 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. 2). 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). 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. The North Anatolian Fault is formed along the Anatolian plate Molnar In addition those three oceanic transforms are not as multibranched as many transform zones on continents. . The earthquakes were analysed using the standard Global CMT (GCMT) algorithm as described in Dziewonski et al. These segments contain fewer events of Mw > 5.9 than that in Fig. We find one segment of the Heezen transform has ruptured quasi-periodically since 1976 in eight shocks of Mw 5.9-6.1 with an average repeat time of 4 yr. We recomputed centroid moment tensor (CMT) solutions for 190 earthquakes along and close to the three transforms of the Eltanin system from 1976 to 2010. 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. . 'dextrally' (also known as right-laterally) which means if you 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. Search for: Recent Posts. Cumulative moment release is shown in Fig. T. COV = 0 and 1.0 correspond to strict periodicity and random occurrence, respectively. 3). For LNADW and AABW, the Romanche and Chain Fracture Zones (just south of the equator) are the only deep passages in the MAR where interbasin exchange is possible. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle. For the period 19902009, we rejected only one event, which occurred on 2001 August 6. 10) was the site of many earthquakes of Mw > 5.55, two of Mw 6.13 and two of Mw 6.0, the latter two on the same day in 2010. The existence of three or four plates in the region during those times permitted offset to grow across the Eltanin system (Watts et al. If the 1981 shock were mislocated at least 12 km eastwards, the length of the repeating segment would be about 30 km. 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. Correct Option: O They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. The steep slope of about -2.9 for Mw > 6 is unusual. The transform valley is 15-20 km wide and 2-4 km deep. Langenhorst 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. slip fault zone between the Caribbean and North American We take this along with the distributions of events in time and longitude after 1976 (Fig. Numbers for 15 yr period 1976-1990 were multiplied by 20/15. Use the facts stated above when they apply. 2. -Linear spreading on Earth's curved surface. transform faults fracture zones and the kinematics of. 3315km (2060mi) WSW of Punta Arenas, Chile . 4 and red symbols in Fig. Indeed, jets are observed to pass along both the Udinstev and Eltanin Fracture Zones (Gille 1994; Hughes and Ash 2001). R.L. The solutions, additional methodology and other pertinent data are described more fully in Appendix A and the Supporting Information. Okal 7 includes an earthquake on 1981 June 20 of Mw 5.94, which was located just to the east of the others at a time when relatively few stations were available for calculating a CMT location. . M. J.J. We find or confirm two anomalous characteristics: the . 2). The Polar and Subantarctic Fronts are observed to pass along the Udinstev Fracture Zone 3 as the jets in the flow are steered by the topography (e.g., Moore et al. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. Cumulative seismic moment release from 1976 to 2010 along a 42-km section of Heezen transform indicated in Fig. The island is very long and narrow. We used a box from 54S to 58S and 140W to 120W to identify earthquakes that might be located on the Eltanin transform system. What kind of fault is represented by the eltanin and romanche fracture zones? L.R. The flow of NADW through the Romanche and Chain Fracture Zones may serve as a conduit for larval transport from the western North Atlantic to the eastern South Atlantic. Anderson The continuity in smooth trend of the ridge and the Eltanin Fracture Zone suggests some relationship between them.