Cumulative seismic moment release from 1976 to 2010 along a 42-km section of Heezen transform indicated in Fig. [3], Series of faults that offset the Pacific-Antarctic Ridge. These species await a formal description and it is not known whether or not they represent communities distinct from those on the northern MAR. Those estimates are smaller than those for oceanic transforms at much slower moving plate boundaries, which is in accord with the notion, which we accept, that temperatures are higher at a given depth for fast moving plate boundaries. . C1. 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. It moves These segments contain fewer events of Mw > 5.9 than that in Fig. , and M is in kg. Hence, remote techniques such as seismicity and satellite altimetry provide important constraints on the tectonics, especially for the Tharp and Hollister transforms. This attests to the very thin lithosphere at fast spreading ridges. Extending the work of Stewart & Okal (1983), they again emphasized the dominance of aseismic slip. Solutions for new earthquakes of Mw > 5.5 were not found after early 2002. 2. C2 shows that Mw is similar to Ms at larger magnitudes but is 0.40.9 units larger at Mw 5.4. Finally we are left with what accounts for transform segments that rupture with high seismic coupling and those with low coupling. A new analysis of plate cooling models indicates that the properties of oceanic lithosphere may need to be reevaluated, or that additional phenomena beyond the conditions of simple mineral physics plate models are important. Dziewonski Map view of CMT locations of earthquakes along Heezen transform and easternmost end of Tharp transform from 1976 to 2010. [3], The Romanche Fracture Zone offsets the Mid-Atlantic ridge by 900km (560mi), making it the largest equatorial fracture zone in the Atlantic. Seafloor magnetic anomalies suggest formation. The existence of three or four plates in the region during those times permitted offset to grow across the Eltanin system (Watts et al. None of our normal-faulting solutions are found adjacent to that part of the Tharp transform. 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. Menke Eltanin fracture zone fracture zone zone of fracture n. , rock fracture zone Mendocino fracture zone oceanic fracture zone deep fracture zone Charlie Gibbs fracture zone - oceanic floor fracture zone M.S. Okal L.R. 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. Numbers for 15 yr period 1976-1990 were multiplied by 20/15. These are too small to represent the actual uncertainties. Only the Heezen transform has been surveyed by swath mapping (Lonsdale 1994). The CMT locations for the Heezen and Hollister transforms and the eastern end of the Tharp are biased to the south of the bathymetric expression of the transforms (Fig. 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. Unless the presence of short spreading centres is taken into account, the application of simple plate cooling models using the entire length of transforms leads to underestimates of temperature and plate coupling. Bergman The two largest (Mw 6.7 and 5.9) occurred well to the north of the transform in 2001 and 2007. The experiment suggests that when the CMT depth is larger than the true depth, the estimated Mo is too high by a small amount. Which letter is pointing to a transform fault? R.G. The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. 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. On the basis of serial hydrographic measurements, the Chain Fracture Zone appears to be separated into several deeper sections. 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). The T-axis of a normal-faulting event in that area of Mw 5.4 in 1978 is inclined about 45 to the transform (Fig. The CMT locations for the Tharp transform are rotated several degrees with respect to both the computed transform direction in Fig. The completeness of the CMT data set as a function of time is described later. 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 slope of -1.0 for the latter period for Mw 5.4-6.0 is typical of that for earthquakes in many areas of the world. The combined three Eltanin transform faults are much more active at the Mw~ 6 level than a comparable length of either the San Andreas Fault in California or other transform systems on land. 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. Use the facts stated above when they apply. 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? He attributed this to changes in the Euler pole for Pacific-Nasca plate motion during the last several million years. (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. The CMT centroid depths for events along the Eltanin system are not accurate enough to define the depths or range of seismic faulting at the level of several to 20 km. 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. . Sunrise, sunset, day length and solar time for Stockholm County. With that assumption we obtain downdip widths of about 5 km for four segments of the Heezen, Tharp and Hollister transforms. Weissel 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. The principal fracture zones are identified, as are segments of the PAR. 4 are more tightly clustered in map view. 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. Data for the reanalysis were collected from all the main global digital networks that have operated since 1976. S1 in the Supporting Information). A.M. . Lamont-Doherty Earth Observatory Contribution 7505. R.E. 6) indicates that it may be a single fault. Hence, we cannot distinguish between those two models. They may be regarded as quasi-periodic. 9 for two sequences of earthquakes along the Tharp transform. How are fracture zones like the Eltanin created? Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. . If those short spreading centres are very young, they may not have had enough time to become oriented perpendicular to the transform. 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. Shen SEANOE. That view was strengthen when Menard reviewed the manuscript and provided an unpublished bathymetric map that included more data in the far southeast Pacific. The segment of the Heezen transform between 29 and 71 km (Fig. E.A. Argus [7] The transform valley is 15-20 km wide and 2-4 km deep. 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. Lonsdale (1994) concludes that a zone of extension north of the Heezen transform developed following a Pliocene change in relative plate motion. We also used the same 3-D velocity model for our new CMT solutions. G. Bohnenstiehl et al. (1988) found that at magnetic chron 34, 83-121 Ma, when New Zealand broke away from Antarctica, there was essentially no fault offset at the location where the Eltanin system was later to develop. We then examine other segments with fewer but larger earthquakes. Which two plates create the Eltanin Fracture Zone? FRACTURE ZONE. Hence, a variety of rupture behaviours, repeat times and maximum observed magnitudes is associated with the active parts of the three transforms. Their 1000 km length is greater than that of any other oceanic transforms at fast-spreading plate boundaries. Whether the depths obtained for normal-faulting events, which occurred off the transforms, applies to strike-slip events along the transforms themselves is equivocal since the velocity and thermal structure of the three transforms is not known and close-in observations with ocean bottom instruments have not been made. Eltanin fracture zone Scope Notes: SE Pacific. 7. The segment near the eastern end of the Heezen transform between 179 and 200 km (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 . Gregg Except for an event in 1975 we did not reanalyse long-period data for earthquakes prior to 1976, but we utilize the approximate locations of some of those larger events in estimating repeat times. G. Events in 2010 were determined in the same manner and are listed in the catalogue of the GCMT project at http://www.globalcmt.org. Individual ridge segments trend, how- ever, up to a few tens of degrees from the smooth trend. 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. Bar at upper right on map shows water depths in metres. Mammericks 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 . E.J. 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. 2). 3 and studied separately. What do the parents perceive as their role to the Day Care worker? No thrust-faulting solutions were found. 4. 4786 km SE of Avarua, Cook Islands / pop: 13,400 / local time: 01:42:15.1 2017-06-15, http://www.emsc-csem.org/Earthquake/earthquake.php?id=524555, Distances: 4676 km SE of Wellington, New Zealand / pop: 381,900 / local time: 06:09:44.3 2016-08-19 Ms, which is typically reported by PDE and ISC only for Rayleigh waves and for periods between about 18 and 22 s, may yield a biased estimate of the long-period character of a seismic source as a result of low excitation at certain focal depths and biased sampling of the radiation field. [5], The hydrothermal vents of the MAR support many life forms. Where is and what is Eltanin Transform Fault and Fracture Zone? 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. They proposed that the Eltanin transforms consisted of small, well-separated asperities that rupture in earthquakes. Correct Option: O They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. Bathymetric Features 67%. Boettcher Depths modelled by Wolfe et al. 4699 km SW of Santiago, Chile / pop: 4,837,295 / local time: 15:09:44.3 2016-08-18 fracture zones and transform faults flashcards quizlet. G. 7, however, since it is located just to the east of other large shocks along the Heezen transform. Exploring Data Coaching Activity: Longshore C, SmartFigure: Geostrophic current and western. For the Eltanin events, this bias is unlikely to be larger than 15 per cent, even for the events with the deepest calculated centroids. Boettcher Earthquakes of Mw > 5.55 were included in each computation. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. stand on one side of it, the other side appears to move to the 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. (1993) attribute it to one of those small spreading centres. The segment of the Hollister transform between -635 and -650 km (Fig. They concluded from analyses of seismograms, however, that the transform earthquakes themselves did not have a significant component of slow seismic slip. 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. R. 7 are the best fit to that model. This bias suggests that the models used for CMT and ISC locations are not slow enough to the north and northeast along the East Pacific Rise. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. Decide for yourself which test is easiest to use, but dont forget the preliminary test. which two plates create the eltanin fracture zone quizlet; Well Inspection using ROV at Kondashetti Halli, Bangalore R.L. Forsyth Their surface wave magnitudes, Ms, for events before 1969 along the Eltanin system were determined typically from one to a few stations. P. The centroid epicentre and time did not shift appreciably in these different inversions, nor did the geometry of the moment tensor change appreciably. 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. D.W. They obtained a depth in the range 8-14 km below the seafloor for the 1978 earthquake off the Heezen fault, and approximately 10 km below the seafloor for the 1989 earthquake off the Tharp transform. Events of Mw > 5.9 account for 70 per cent of the moment in Fig. The feature was then named the Eltanin fracture zone. The CMT methodology and format of the catalogue are described in Dziewonski (1981) and Ekstram (2005). Hence, it and the two larger events occurred along an off-transform feature. It and some other segments of the three Eltanin transforms appear to be well coupled seismically. At 14.5W the trough reaches a maximum depth of 2895 fm (5470 m). The Fracture Zone is located at the latitude and longitude coordinates of -54 and -130. The smaller events in Fig. GE was partially supported by NSF grant EAR-09-24694. (2010) that describes the relative motion of the Pacific and Antarctic plates. 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. . It is therefore unlikely that the event selection for 19902009 missed any earthquake with a moment magnitude greater than 5.5. 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. 4), to constrain their source depths. Centroid moment tensor solutions are recomputed for 190 earthquakes from 1976 to 2010 along the Heezen, Tharp and Hollister transform faults of the Eltanin system using a 3-D seismic velocity model. This technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots.
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