Empirical analysis of path effects on prediction equations of pseudo‐velocity response spectra in northern Japan

We study path effects on prediction equations of pseudo‐velocity response spectra (natural period of 0.1–5.0 s) in northern Japan, where heterogeneous attenuation structure exists. The path effects have been examined by comparing the regression analysis results for two different prediction equations. The first equation consists of a single term of anelastic attenuation conventionally. The second equation consists of two terms of anelastic attenuation in consideration of the heterogeneous attenuation structure. In the second equation, we divide a source‐to‐site distance into two distances at the attenuation boundary beneath the volcanic front. The boundary is considered to separate the relatively high Q fore‐arc side mantle wedge (FAMW) from the low Q back‐arc side mantle wedge (BAMW). Strong motion records (hypocentral distances less than 300 km) from interplate and intraslab events with Mw 5.1–7.3 are used. Regression analysis results show that the standard errors are significantly reduced by the second prediction equation at short periods (0.1–0.5 s), whereas the difference in standard errors from both prediction equations is negligible at intermediate and long periods. The Qs values (quality factor for S‐wave) converted from two anelastic attenuation coefficients for the second prediction equation are remarkably similar to the path‐averaged Qs values for the FAMW and BAMW by other studies using spectral inversion method. From these findings, we conclude that the path effects on the prediction equation of pseudo‐velocity response spectra are satisfactorily accomplished by the second prediction equation. Copyright © 2009 John Wiley & Sons, Ltd.     

Source parameters of some presumed Semipalatinsk underground nuclear explosions

Summary Short-period vertical-componentP-wave spectra of seven presumed Semipalatinsk underground nuclear explosions, recorded by the Swedish seismic station network, are investigated. The events considered have closely spaced foci and cover the magnitude range fromm _b=5.5 tom _b=6.6. Spectra of six of these explosions show pronounced minima, varying from about 1.5 to 1.8 cps, which could be explained as principle minima due toP-pP interference. Supposing a nearsurfaceP-wave velocity at the test area of 4 km/sec, the shot depths are estimated to vary roughly from 750 to 1350 m. In order to obtain an estimate of the yield, the observed spectra are compared withHaskell's theoretical source spectra. For four events, relative yield estimates fit well the predicted values for explosions fired in a granitic medium. The behaviour of the remaining three explosions is discussed in detail.     

P-wave amplitude spectra of Nevada underground nuclear explosions

Summary Short-period vertical-componentP-wave spectra have been determined for twelve Nevada underground nuclear explosions recorded by the Swedish seismic station network. Selected events cover the magnitude range fromm _b =5.9 tom _b =7.0 and the shot-depth range from 460 m to 1400 m. All explosion spectra show pronounced minima near 1 sec period. Within individual test areas the period at which the minimum occurs increases systematically with increasing shot-depth. This dependence makes it possible to interpret the observed minima in terms of interference betweenP- andpP-waves. One atmospheric explosion from Novaya Zemlya is analyzed to verify the inferred minima intrpretation.The minimum-period shows also a systematic linear dependence upon the magnitude. However, the physical explanation for this dependence is not evident and it may just be a consequence of a magnitude-depth relation.On leave from the Geophysical Institute, Czechosl. Acad. Sci., Prague 4-Spoilov, Boni II.     

Algal lipids as a possible contributor to the polymethylene chains in kerogen

Lipid fraction and cell-wall materials have been separated from three types of algae (blue green, Microcystis sp.; green, Scenedesmus sp. and diatomaceous Diatoma sp.) and their KMnO₄ oxidation products (aliphatic $\text{α,ω-C}{}_2\text{-C}{}_{12}$ dicarboxylic acids; aliphatic normal C₁₄–C₂₄ monocarboxylic acids; benzoic acid and C₁₈ isoprenoidal ketone) examined by gas chromatography and gas chromatographymass spectrometry. The results suggest that the lipid material could make a greater contribution to polymethylene chains in kerogen than the cell-wall material, when the kerogens are mainly derived from algal components.     

Sequential solutions with the bandtype system of Observation equations

The construction of formulas for sequentially computing solutions and a variance-covariance matrix with the bandtype system of observation equations, which is inherent in geodetic networks, is carried out; these formulas are illustrated with a simple numerical example in which the adjustment for the trilateration of triply coupled quadrilaterals is executed.     

P-wave velocity anomalies in the earth's mantle from the Uppsala array observations

Summary Distribution of compressional-wave velocities in the mantle is determined fromdT/d measurements using the Uppsala seismograph array station (UPSAS). Short-period vertical-component seismograms from 181 events in the epicentral distance range 16°–100° have been used. The velocity distribution shows anomalous variations at depths of 750, 1500, 1800, 2300 and 2550 km. Evidence of lateral heterogeneity beneath the northern part of the Asian continent, in the depth range 1700–2300 km, is discussed. Computed travel times, based on this velocity-depth relation, are tested by an examination of travel-time residuals from the Long Shot and Milrow explosions on Amchitka, Aleutian Islands.     

Early stage incorporation of biolipids into kerogen in a lacustrine sediment: Evidence from alkaline potassium permanganate oxidation of sedimentary lipids and humic matter

Lipids, fulvic acid, humic acid and kerogen were isolated from a lacustrine sediment in which the organic matter is probably derived predominantly from phytoplankton (Lake Haruna, Japan). An alkaline KMnO₄ oxidation study of the organic matter showed that distributions of polymethylene chain lengths in the lipids, humic acid and kerogen fractions are almost the same. The polymethylene chains in the sediment are dominant in the kerogen, lipids and humic acid, their relative abundance estimated by the oxidation being: kerogen (42% of the total amounts of polymethylene chains estimated) > lipids (38%) > humic acid (19%) > fulvic acid (1%). It was concluded that algal lipids may have been incorporated into the kerogen and humic acid fractions after the death of the algae and during, after, their deposition.     

Holocene coastal uplift in the western Pacific Rim in the context of late Quaternary uplift

This paper reviews recent studies of Holocene coastal uplift in tectonically active areas near the plate boundaries of the western Pacific Rim. Emergent Holocene terraces exist along the coast of North Island of New Zealand, the Huon Peninsula of Papua New Guinea, the Japanese Islands, and Taiwan. These terraces have several features in common. All comprise series of subdivided terraces. The highest terrace is a constructional terrace, underlain by estuarine or marine deposits, and the lower terraces are erosional, cutting into transgressive deposits or bedrock. The highest terrace records the culmination of Holocene sea-level rise at ca. 6–6.5 ka BP. Lower terraces were coseismically uplifted. Repeated major earthquakes have usually occurred at ka intervals and meter-scale uplift. The maximum uplift rate and number of terraces are surprisingly similar, about 4 m/ka and seven to four major steps in North Island, Huon Peninsula, and Japan. Taiwan, especially along the east coast of the Coastal Range, is different, reaching a maximum uplift rate of 15 m/ka with 10 subdivided steps. They record a very rapid uplift. Comparison between short-term (Holocene) and long-term since the last interglacial maximum (sub-stage 5e) uplift rates demonstrates that a steady uplift rate (Huon Peninsula) or accelerated uplift toward the present (several areas of Japan and North Island) has continued at least since isotope sub-stage 5e. Rapid uplift in eastern Taiwan probably started only in the early Holocene, judging from the absence of any older marine terraces. Most of the causative faults for the coastal uplift may be offshore reverse faults, branched from the main plate boundary fault, but some of them are onshore faults, which deformed progressively with time.     

Review of paleoseismological and active fault studies in Taiwan in the light of the Chichi earthquake of September 21, 1999

This paper reviews the research on active and earthquake faults in Taiwan conducted prior and after the 1999 Chichi earthquake. The Chichi earthquake plays as a turning point of the relevant studies, since the 1999 coseismic surface rupture exactly follows preexisting fault scarps, created in turn by previous seismic events along the Chelungpu Fault. This fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes. Since 1999, many trenching studies have been carried out along the Chichi earthquake fault. A few of them demonstrates that the penultimate event is as young as probably only 200–430 years old; however, some others show a rather old age of several hundreds years or even older for the last faulting event before 1999. More trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length. In addition, we further discuss the offshore faulting associated with seismic event along the eastern coast of Taiwan, where the multiple Holocene terraces are well known.     

Bathymetry, biota and sediments on the Hirota Reef, Tane-ga-shima – the northernmost coral reef in the Ryukyu Islands

Abstract Investigations were conducted on bathymetry, reef biota and sediments on the Hirota Reef, Tane‐ga‐shima, North Ryukyus, near the northern limit for coral‐reef formation. A bathymetric profile from shore to the reef edge was depicted along an approximately 420‐m transect on the Hirota Coast of this island. A total of 20 quadrats (1 m × 1 m) were analyzed along the profile at 10‐ or 20‐m intervals to clarify distribution of macrobenthos inhabiting the reef. The Hirota Reef is divided into four geomorphologic zones according to their depth, gradient, surface roughness, substrate and characteristic macrobenthos. They are, from shore to offshore, shallow lagoon, seaward reef flat, reef edge and reef slope. The shallow lagoon comprises a shoreward depression (∼160 m wide on the transect) with a sand/gravel bottom that inclines gently toward offshore, and a seaward patch zone (∼70 m wide). The patches (<2 m high) are covered with fleshy algae, coralline algae and hermatypic corals. The seaward reef flat (∼190 m wide) is a flat plane that is constructed by biogenic carbonates and is covered with turf algae, with hermatypic corals scattered. Although the seaward reef flat of the Hirota Reef cannot be differentiated into different geomorphologic zones, similar seaward reef flat areas in the Central and South Ryukyus can be clearly subdivided into inner reef flat, reef crest and outer reef flat. This difference may be attributed to a lower reef growth rate and/or the later reef formation of the Hirota Reef in Holocene time than the southern examples. The coral fauna on the Hirota Reef is delineated by low diversity and characterized by taxa typical of high‐latitude, non‐reefal communities. The algal flora consists of tropical to subtropical species associated with warm‐temperate species. These faunal and floral characteristics may be related largely to lower water temperature in Tane‐ga‐shima than those in typical coral‐reef regions.