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Analysis of three first-order leveling lines that traverse the White Wolf fault (site of the 1952 M = 7.7 earthquake), each resurveyed nine times between 1926 and 1974, reveals probable preseismic tilting, major coseismic movements, and a spatial association between these movements and the subsequently recognized southern California uplift. In examining the vertical control record, we have both searched for evidence of systematic errors and excluded from consideration portions of the lines contaminated by subsurface fluid and gas extraction. Movements have been referred to an invariant datum based on the 1926 position of tidal BM 8 in San Pedro, corrected for subsequent eustatic sea-level change.An 8 μrad up-to-the-north preseismic tilt (6 cm/7.5 km) was apparently recorded on two adjacent line segments within 10 km of the 1952 epicenter between 1942 and 1947. It is possible, however, that this tilt was in part caused by extraction-induced subsidence at one of the six releveled benchmarks. Data also show evidence of episodic tilts that are not earthquake related. At the junction of the Garlock and San Andreas faults, for example, an ≥5 μrad up-to-the-north tilt (7.2 cm/≤16 km) took place between Lebec and Grapevine within three months during 1964.Comparison of the 1947 and 1953 surveys, which includes the coseismic interval, shows that the SW-fault end (nearest the epicenter) and the central fault reach sustained four times the uplift recorded at the NE end of the fault (+72 cm SW, +53 cm Central, +16 cm NE). A regional postseismic uplift of 4 cm extended ≥25 km to either side of the fault after the main event, from 1953 to 1956. An interval of relative quiescence followed at least through 1959, in which the elevation change did not exceed ±3 cm.The detailed pattern of aseismic uplift demonstrates that movement proceeded in space—time pulses: one half of the uplift at the SW-fault end and extending southward occurred between 1959 and 1961, one half of the uplift at the NE-fault end and extending eastward occurred between 1961 and 1965, while the central fault reach sustained successive pulses of subsidence, uplift, and collapse (−4 cm, 1953–1960; +7 cm, 1960–1965; −2 cm, 1965–1970). In addition, the number of aftershocks concentrated near the fault ends increased in the NE relative to the SW from 1952 to 1974. These observations suggest that the aseismic uplift may have migrated northeastward from 1959 to 1965 at an approximate rate of 7–16 km/yr.Evidence for a mechanical coupling between the earthquake and the subsequent aseismic uplift is equivocal. At both fault ends, the major NWbounding flexure or tilted front of the southern California uplift is spatially coincident with the coseismic flexure that preceded it. In addition, the postulated migration of vertical deformation is similar to the 1952 seismic event in which the rupture initiated at the SW end of the fault and then propagated to the NE-fault end. However, the spatial distribution of aseismic uplift, nearly identical at both fault ends and to the south and east, and near zero in the central fault reach, is distinctly different from the nonuniform and localized coseismic deformation. 相似文献
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Market studies by Hydro Products identified industry interest in a guide wire deployed package consisting of an RCV-225 remotely controlled vehicle with launcher and a strong dexterous manipulator for drill ship support in water depths to approximately 2000 ft (sim 600 m). This paper discusses the design, production, and initial testing of a prototype unit. Anticipated capabilities provided for in the initial design include the ability to perform pre- and post-drilling site surveys, wellhead and riser television inspection, stabbing assist, AX/VX ring replacement, guide wire replacement assist, and debris removal. Provision for incorporation of further sensors and capabilities was given high priority. Future developments and plans for further testing are also enumerated. 相似文献
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A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central
caldera floor near Le Hardy Rapids rose 24±5 mm relative to the caldera rim at Lake Butte since the previous survey in September
1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average
rate of –19±1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923–1976 (14±1 mm/year)
and 1976–1984 (22±1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic
aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995
to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast
part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993
to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome
by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are
caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5–10 km depth, near the interface
between Yellowstone's magmatic and deep hydrothermal systems.
Received: 30 November 1998 / Accepted: 16 April 1999 相似文献
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Di Virgilio Giovanni Evans Jason P. Di Luca Alejandro Grose Michael R. Round Vanessa Thatcher Marcus 《Climate Dynamics》2020,54(11):4675-4692
Climate Dynamics - Coarse resolution global climate models (GCMs) cannot resolve fine-scale drivers of regional climate, which is the scale where climate adaptation decisions are made. Regional... 相似文献