Number of Polygons Generated by Map Overlay: The Case of Convex Polygons

This paper analyzes the number of polygons generated by map overlay. Overlay of maps yields a number of small polygons, and often causes problems in computation, handling, and storage of derived polygons. One method to deal with these problems is to estimate the number of derived polygons before executing overlay operation. To this end, a stochastic model is proposed by which the expected number of derived polygons is calculated. The results are summarized as follows: (1) the number of polygons generated by map overlay depends on the number of original polygons and their perimeters; (2) the number of derived polygons increases with the perimeters of original polygons; (3) McAlpine and Cook's (1971) earlier method underestimated the number of derived polygons; and (4) the number of polygons generated by the overlay of maps having the same lattice system is proportional to the square of the number of overlaid maps and the number of polygons on the map, and inversely proportional to the area-perimeter ratio of the unit cell.     

Origin of ureilites inferred from a SIMS oxygen isotopic and trace element study of clasts in the Dar al Gani 319 polymict ureilite

Secondary ion mass spectrometer (SIMS) oxygen isotope analyses were performed on 24 clasts, representing 9 clast types, in the Dar al Gani (DaG) 319 polymict ureilite with precisions better than 1‰. Olivine-rich clasts with typical ureilitic textures and mineral compositions have oxygen isotopic compositions that are identical to those of the monomict ureilites and plot along the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line. Other igneous clasts, including plagioclase-bearing clasts, also plot along the CCAM line, indicating that they were derived from the ureilite parent body (UPB). Thus, we suggest that some of the plagioclase-bearing clasts in the polymict ureilites represent the “missing basaltic component” produced by partial melting on the UPB.Trace element concentrations (Mg, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Sr and Ba) in ureilitic plagioclase and glass from 13 clasts were obtained by using the SIMS high mass resolution method. The trace element contents of the plagioclase generally show monotonic variations with anorthite content (mol%) that are consistent with partial melting and fractional crystallization. Incompatible trace element concentrations (K, Ti, and Ba) are low and variable for plagioclase with An > 40, indicating that the parental magmas for some clasts were derived from a depleted source. We performed partial melt modeling for CI and CM precursor compositions and compared the results to the observed trace element (K, Ba, and Sr) abundances in the plagioclase. Our results indicate that (1) the UPB evolved from a alkali-rich carbonaceous chondritic precursor, (2) parent melts of porphyritic clasts could have formed by 5-20% equilibrium partial melting and subsequent fractional crystallization, and (3) parent melts of the incompatible trace element-depleted clasts could be derived from fractional melting, where low degree (<10%) partial melts were repeatedly extracted from their solid sources.Thus, both the oxygen isotopic and trace element compositions of the plagioclase bearing clasts in DaG-319 suggest that the UPB underwent localized low degree-partial melting events. The partial melts could have been repeatedly extracted from the precursor, resulting in the formation of the olivine-pigeonite monomict ureilites as the final residue.     

Automatic extraction of lineament information from satellite images using digital elevation data

Using conventional visual interpretation in lineament analysis presents two main problems. The first is subjectivity, introduced because of the bias of various interpreters. The second problem is that lineaments detected from satellite images are constrained by the direction of the illumination source. Since lineament identification mainly involves recognition of diagnostic morphological features, the use of digital elevation can contribute significant information about these features. Further, in generating images using digital elevation data, the direction of illumination can easily be controlled. Thus, the use of digital elevation data offers the possibility of revealing features not apparent in regular satellite images.We discuss a sequential line detection method for extraction of linear features from digital elevation data. In this method, raw elevation data is used for generating shaded relief images using the Lambertian reflection model, wherein the illumination direction is controlled by the user. The Directional Segment Detection Algorithm (DSDA) is used for detecting linear topographic features in user-defined trends. Locational information about these linear features is stored in the computer as coordinate pairs amenable to editing and subsequent analysis. Finally, three-dimensional terrain models are generated by combining the digital elevation data and satellite images. The experiments were carried out using digital elevation data of southwest Japan and Landsat MSS data.     

The birth and evolution of an eastward propagating air-sea coupled disturbance in an aqua-planet

Summary The birth and evolution of an air-sea coupled disturbance relevant to the El Niño/Southern Oscillation (ENSO) events is investigated using a simple coupled aqua-planet model composed of the Gill's moist atmosphere and the Anderson-McCreary ocean. A coherent air-sea coupled disturbance with the zonal wavenumber 1 emerges from different initial disturbances either in the atmosphere or the ocean and propagates eastward as observed in the 1982/83 event. In the case of an initial westerly wind burst, oceanic Kelvin waves generated by the winds cause weak but long-lasting ocean temporature anomalies which trigger the air-sea coupled disturbance. When the initial disturbance is in the oceanic mixedlayer temperature, the coupled disturbance is excited more easily because the oceanic relaxation time is long compared to the atmospheric one. This is consistent with the result that the coupled disturbance collapses when the disturbance is forced to vanish on the oceanic side rather than on the atmospheric side.With 8 Figures     

A widespread simultaneous increase of the microearthquake seismicity and minor crustal movements in and around the assumed rupture zone of the Tokai earthquake

Data from an extensive routine network and a high-density temporary seismic observation using the ocean bottom seismometer in and around Suruga Bay, Japan, showed that a simultaneous increase of microearthquake seismicity occurred from mid-July 1984 (Ukawa et al., 1988). The area extended over a region of about 60 km (NS) × 80 km (EW), and is nearly included in the assumed fault zone of the presumed Tokai earthquake. The analyses of the bore-hole ground tilt and volumetric strain data revealed that an anomalous small ground tilt and volumetric strain change occurred at the time of the seismic activity with a duration of about a month. Data of geodetic measurements, groundwater, and radon content were examined with the result that many observational items showed small anomalies during that period. The observed crustal movement was compared with that of slip models of the Philippine Sea plate around Suruga Bay, suggesting that some type of episodic aseismic subducting motion occurred and, thus, caused a crustal movement in the overlying continental plate in the very region of the future fault zone.     

Probability of earthquake occurrence as obtained from a Weibull distribution analysis of crustal strain

Probability of a large-scale earthquake occurrence is estimated from crustal strain geodetically detected over an earthquake area. The Weibull distribution function, which is widely applied to quality-control research, is made use of in this paper in the probabilistic treatments of crustal strain.Using the table of ultimate strain presented by Rikitake (1974), a Weibull model representing a statistical distribution of crustal-rupture occurrence time is determined on the assumption that the crust is strained with a constant speed. In the case of the South Kanto District, the associated probability-density function has a maximum at about 84 years after the time when the strain energy accumulation starts.     

Anatomy and genesis of a subduction-related orogen: A new view of geotectonic subdivision and evolution of the Japanese Islands

Abstract The Japanese Islands represent a segment of a 450 million year old subduction-related orogen developed along the western Pacific convergent margin. The geotectonic subdivision of the Japanese Islands is newly revised on the basis of recent progress in the 1980s utilizing microfossil and chronometric mapping methods for ancient accretionary complexes and their high-P/T metamorphic equivalents. This new subdivision is based on accretion tectonics, and it contrasts strikingly with previous schemes based on‘geosyncline’tectonics, continent-continent collision-related tectonics, or terrane tectonics. Most of the geotectonic units in Japan are composed of Late Paleozoic to Cenozoic accretionary complexes and their high-PIT metamorphic equivalents, except for two units representing fragments of Precambrian cratons, which were detached from mainland Asia in the Tertiary. These ancient accretionary complexes are identified using the method of oceanic plate stratigraphy. The Japanese Islands are comprised of 12 geotectonic units, all noted in southwest Japan, five of which have along-arc equivalents in the Ryukyus. Northeast Japan has nine of these 12 geotectonic units, and East Hokkaido has three of these units. Recent field observations have shown that most of the primary geotectonic boundaries are demarcated by low-angle faults, and sometimes modified by secondary vertical normal and/or strike-slip faults. On the basis of these new observations, the tectonic evolution of the Japanese Islands is summarized in the following stages: (i) birth at a rifted Yangtze continental margin at ca 750–700 Ma; (ii) tectonic inversion from passive margin to active margin around 500 Ma; (iii) successive oceanic subduction beginning at 450 Ma and continuing to the present time; and (iv) isolation from mainland Asia by back-arc spreading at ca 20 Ma. In addition, a continent-continent collision occurred between the Yangtze and Sino-Korean cratons at 250 Ma during stage three. Five characteristic features of the 450 Ma subduction-related orogen are newly recognized here: (i) step-wise (not steady-state) growth of ancient accretionary complexes; (ii) subhorizontal piled nappe structure; (iii) tectonically downward-younging polarity; (iv) intermittent exhumation of high-P/T metamorphosed accretionary complex; and (v) microplate-induced modification. These features suggest that the subduction-related orogenic growth in Japan resulted from highly episodic processes. The episodic exhumation of high-P/T units and the formation of associated granitic batholith (i.e. formation of paired metamorphic belts) occurred approximately every 100 million years, and the timing of such orogenic culmination apparently coincides with episodic ridge subduction beneath Asia.     

Spectroscopic properties of Cr-doped melilite crystals

 Four kinds of Cr-droped melilite crystals, Ca₂MgSi₂O₇ (akermanite), CaAl₂SiO₇ (gehlenite), CaGa₂SiO₇ (Ga-gehlenite) and CaGa₂GeO₇ (GaGe-gehlenite), with different sizes of the sites for Cr ions to substitute, were grown in series, using both the CZ and FZ techniques. Although Cr⁴⁺ is regarded as a major species in melilites, the existence of Cr⁶⁺ in gehlenite is also suggested from the change in absorption spectra by annealing, and the dependence of distribution coefficient of Cr ions on growth atmosphere. Spectral peak shifts are not obvious if the host crystal field is altered in melilites, because the local environment of the sites for Cr ion is possibly changed by reforming the packing features of the host lattice. Received February 7, 1996 / Revised, accepted September 20, 1996     

Effects of Interannual Variability in the Eastern Indian Ocean on the Indonesian Throughflow

The influences of the large-scale interannual variations in the eastern Indian Ocean on the variability of the Indonesian throughflow are investigated by using an ocean general circulation model, driven by the ERS satellite winds from July 1992 to June 1997. The empirical orthogonal function (EOF) analysis of the simulated surface dynamic height variability captures two dominant modes on an interannual time scale, which are quite consistent with the available observations. The first mode indicates large amplitude in the western tropical Pacific and has a strong relation to the El Niño events, while the second EOF exhibits the large amplitude in the eastern Indian Ocean. The simulated net Indonesian throughflow shows an interannual variation of amplitude of about 15 Sv, with large transport from the Pacific to the Indian Ocean during 1994/95 and small transport during 1992 and 1997. It turns out that the net throughflow variation shows a high correlation with the second EOF mode (r = 0.51) for the whole five-year simulation. On the other hand, the correlation with the first mode is rather low (r = ?0.07). However, the relative importance of the EOF modes to the throughflow variability changes with time. The upper-layer transport above a depth of 230 m in the Indonesian archipelago is also affected by the second mode. The difference in the upper-layer transport across 1°S and 110°E generates warm water convergence/divergence with a magnitude of 4 Sv within the Indonesian Seas on the interannual time scale, which shows good correspondence with sea surface temperature variation averaged over the Indonesian archipelago.