摘要:

SeaMARC II sidescan imagery casts new light on glacigenic mass‐wasting on the Bear Island Fan, whose surface geology is evidently much more complex (Figure 1) than the regular bathymetric contours had indicated. The University of Bergen research vesselHåkonMosby towed a SeaMARC II side‐scan sonar/bathymetric swathmapping system along the Svalbard‐Barents Sea continental margins and across the Mohns‐Knipovich‐Molloy spreading axis [Sundvor et al., 1990] in October and November 1989 and again in September and October 1990. Magnetic, 3.5‐kHz, and gravity data were also collected along parts of the survey area.The plate boundary was the primary campaign target, but significant discoveries were also made on the reconnaissance tracks across and along portions of the margins, mostly below 800‐ to 1000‐m depths (P. Vogt et al., unpublished manuscript, 1993). We summarize our work over the central and northern quadrants of the Bear Island Fan (Figure 2), where the sidescan revealed unusual mass‐wasting in the form of numerous thin (10–20 m), 5‐ to 20‐km‐wide mudflows up to 200 km

ISSN:0002-8606    

DOI:10.1029/93EO00370

年代:1993

数据来源: WILEY

摘要:

Criticisms of well‐established scientific doctrine can be stimulating and productive even if done by a single individual or a small group. Such criticisms, however, must meet the usual standards of scientific work. Since the concept of prolonged solar activity minima was resurrected byEddy[1976], a small number of publications have argued for the nonexistence of the Maunder Minimum (approximately 1645–1715), and, by implication, of other prolonged solar minima [e.g.,Schröder and Treder, 1993]. In this paper, I shall briefly try to clarify the points of apparent disagreement, concerning myself primarily with auroral data. I conclude that there is, at this time, no real disagreement and that the apparent differences deal more with the nature of the minima rather than the existence of the mi

ISSN:0002-8606    

DOI:10.1029/93EO00513

年代:1993

数据来源: WILEY

摘要:

Occasionally in intraplate areas, isolated swarms of small earthquakes occur with hypocenters only a kilometer or two apart, many kilometers away from any other seismic activity [Crampin, 1991]. The Blue Mountain Lake swarm, N.Y., 1972–1973, and the Enola swarm, Ark., 1982–1983, were two such swarms.The largest events in isolated swarms, which I shall call “typical events,” are usually smaller than magnitude 4 and typically tend to repeat with similar magnitudes and locations every few days or weeks. These typical events have shown precursory phenomena similar to those seen before much larger earthquakes in regions of higher seismicity. Changes in Vp/Vs ratios were observed at Blue Mountain Lake [Aggarwal, 1973] and at Enola [Chiu et al., 1984], and changes in shear‐wave splitting were also observed at Enola [Booth et al., 1990]. Presumably the reason for the sensitivity that allows precursors to be observed before comparatively small events in isolated swarms is that the behavior before small earthquakes can be identified in quiet aseismic areas that would be hidden in the tectonic complexity of more active seismi

ISSN:0002-8606    

DOI:10.1029/93EO00486

年代:1993

数据来源: WILEY

摘要:

Leg 149 of the Ocean Drilling Program drilled a transect of basement holes across the ocean‐continent transition (OCT) of the rifted continental margin off the west coast of Portugal. The principal objective was to sample a series of basement highs beneath the Iberia Abyssal Plain, which were thought to span the transition from the oldest oceanic crust to a peridotite ridge separating oceanic from extended continental crusts to a broad region of highly‐extended continental crust.Drilling demonstrated that the late rift‐stage exposures of peridotite at the seafloor are more laterally extensive than previously thought; peridotite was found on two highs 19 km apart. From the region expected to be extended continental crust, we cored 57 m of metagabbro basement whose continental or oceanic affinities are not yet clear. This rock may be Hercynian in age, and therefore part of the continental crust that was rifted to form this margin, or it may have been emplaced, uplifted, and exposed during rifting some 125 m.y.a. At our most landward site, Tithonian sediments, deposited about 20 m.y. before the onset of seafloor spreading on this segment of margin, are interpreted to overlie extended continental crust. The results of the leg will shed new light on the mechanisms by which upper mantle and perhaps lower crustal rocks are exposed at the seafloor during the late stages of continental br

ISSN:0002-8606    

DOI:10.1029/93EO00493

年代:1993

数据来源: WILEY

摘要:

“Applications of Research from the U.S. Geological Survey Program, Assessment of Regional Earthquake Hazards and Risk Along the Wasatch Front, Utah” (USGS Professional Paper 1519) is a report that explains how new information about earthquake hazards was applied in Utah. The report, edited by Paula Gori, is now available.In 1983, the USGS targeted the Wasatch Front, Utah, for a multiyear program that focused on earthquake research and hazards reduction. An earlier report, “Assessment of Regional Earthquake Hazards and Risk Along the Wasatch Front, Utah” (USGS Professional Paper 1500 A‐J) contained the results of much of the scientific research undertaken from 1983 to 1988. This new report contains the results of research undertaken during the latter phases of the Wasatch Front Program and presents examples of how the research was applied at the lo

ISSN:0002-8606    

DOI:10.1029/93EO00537

年代:1993

数据来源: WILEY