摘要:

To investigate the thermal, chemical, and mechanical behavior of magma during its ascent toward the surface, four holes were continuously cored into an igneous system young enough to be essentially unchanged since its emplacement. The system investigated was the 600‐year‐old Inyo chain of rhyolitic domes and flows in Long Valley, California (Figure 2). Three holes were drilled in or adjacent to Obsidian Dome at the north end of the chain, just outside the Long Valley caldera. One was drilled beneath the phreatic south Inyo Crater, at the south end of the chain in the west moat of the caldera.The first hole was drilled in 1983 and penetrated the side of the lava dome, and continued into the underlying Tertiary basalt. The second hole, drilled in 1984, intersected and passed through the dome's vent and into Sierran granitic rock. The third hole, also drilled in 1984, sampled the rhyolitic feeder dike 1 km south of the dome's vent, where the magma did not reach the surface. The dike is part of the shallow dike system that underlies the Inyo ch

ISSN:0002-8606    

DOI:10.1029/89EO00215

年代:1989

数据来源: WILEY

摘要:

The Baltic Sea is a shallow, semi‐enclosed brackish water basin located in North Europe. Sea ice occurs there every winter, with the annual cover varying from 12 to 100%. There is a strong need for operational sea ice mapping due to intensive ship traffic assisted by 20–30 powerful icebreakers. Sea ice reports and charts are provided daily by ice services in all countries in the Baltic Sea area. In Finland and in Sweden, much effort is put into ice research in support of winter navigation [e.g., Leppdranta, 1986; Thompson, 19

ISSN:0002-8606    

DOI:10.1029/89EO00216

年代:1989

数据来源: WILEY

摘要:

We read with great interest the news report inEos(June 16, 1989) on the very large Macquarie earthquake of May 23, 1989, which left U.S. scientists divided as to whether this earthquake was of strike slip or thrust type or a mixture of both.Indeed, we think we have the solution to this dilemma, since thanks to teletransmitted data from 11 Geoscope stations recording both very long‐period and broad band data, we were able to obtain a reliable preliminary mechanism less than 48 hours after this earthquake occurred. Figure 1 shows this mechanism, which is a practically pure right‐lateral strike slip, consistent with the general trend in the Macquarie ridge area as indicated from the CMT catalog for the past 10 years [Dziewonski et al.,1989], and in particular, very similar to the mechanisms of the two largest events which occurred in this area in this time period (May 25, 1981 and July 7, 1982). By moment tensor inversion of very long‐period Rayleigh waves, we obtained a moment of 2.2×1028dyne‐cm and a centroid time of 28 s, which yields a rating for this earthquake as “average‐to‐fast” with respect to the moment/duration relation. So far, we haven't found any conclusive evidence for strong horizontal directivity, while it seems that the rupture may have extended down to (or up from) at least 40 km. These features of the solution offer a good explanation as to why no tsunami was observed for this earthquake. The confidence in our “very‐long period” solution comes from its very good compatibility with broad band data from the three teletransmitted Geoscope stations that lie within the epicentral distance range 30°−90° from the epicenter of the Macquarie event, both in terms of mechanism as well as source duration. For shallow earthquakes the earthquake depth and the vertical dip‐slip components of faulting are poorly constrained by the very‐long period data. The addition of only a few broad band seismograms in the analysis can remove this uncertainty. Figure 2 shows two examples of fits for SH waves obtained in a combined analysis of long‐period surface waves and broad band body waves [Ekstrom,1989]. The teleseismic SH arrival at Papeete had an amplitude of 0.9 mm. The Macquarie region lies so far south in the southern hemisphere that very few records from existing broad band digital stations appropriate for mantle P and S wave analysis will ever be available. For Geoscope (which presently counts 20 operational broad band digital stations), besides PPT (Tahiti), KIP (Hawaii) and RER (Reunion Island), which were teletransmitted (CAN, Australia,is too close), we still expect data in this distance range from stations NOU (New Caledonia), DRV (Dumont d'Urville), PAF (Kerguelen) and CRZF (Crozet Island), the last three of which will take several months to arrive because they will travel part of the way by ship. Table 1 lists the coordinates and position with respect to the epicenter of the 11 stations

ISSN:0002-8606    

DOI:10.1029/89EO00220

年代:1989

数据来源: WILEY

摘要:

Field investigations of the Malaspina Glacier, Alaska (Figure 1), were conducted by the U.S. Geological Survey in late September 1988, to examine areas of the glacier's surface which had produced unusual backscatter responses (see cover and Figure 2) on X‐band side‐looking airborne radar (SLAR). SLAR imagery of the Malaspina Glacier was collected for the USGS by INTERATechnologies, Inc., in November 1986, as part of a systematic program to produce radar image mosaics of the Yakutat, Mt. Fairweather, Mt. Saint Elias, Icy Bay, and Bering Glacier 1° × 2° quadrangles. These data are the first digitally acquired, X‐band, high‐resolution, synthetic aperture radar (SAR) of coastal, south central Alaska and the Malaspina Glacier. The Xband SLAR operates at a frequency of 9.6 GHz with a wavelength of 3.2 cm. The only other previously available, nonproprietary, SAR imagery of the Malaspina Glacier is much lower‐resolution, L‐band, SEASAT SAR, obtained in 1978. SEASAT operated at a frequency of 1.3 GHz with a wavelength of 23.5 cm. The resolution of SEASAT is about 25 m, while the SLAR data have a resolution of about 10 m. The backscatter features observed on the X‐band SLAR imagery are only poorly discernibl

ISSN:0002-8606    

DOI:10.1029/89EO00221

年代:1989

数据来源: WILEY

摘要:

To maximize our ability to obtain recognition of Ocean Sciences Section members as Fellows of AGU while minimizing the associated workload, I have, in consultation with our executive committee, established an Ocean Sciences Fellows Committee chaired by the President‐Elect to oversee and assist in the nomination process.The committee asks that anyone wanting to make a nomination send a one‐page proposal telling why an individual should be a Fellow. Proposals will be reviewed by the commitee, and a number equal to 1½ to 2 times our nomination quota will be chosen for full presentation. Committee members will then work with nominators to select and contact seconders, while the nominator provides the required curriculum vitae and publication list. The committee will assist in any manner possible to insure that the files that go forward are both timely and well docume

ISSN:0002-8606    

DOI:10.1029/89EO00217

年代:1989

数据来源: WILEY

ISSN:0002-8606    

DOI:10.1029/EO070i028p00710-01

年代:1989

数据来源: WILEY