Hybrid experiments on non-linear earthquake-induced soil-structure interaction

Non-linear seismic soil-structure interaction is studied through a hybrid procedure using the pseudo-dynamic testing (PDT) method which is modified to take into account frequency dependence and developed for foundation-soil systems. The numerical scheme used in conventional PDT is improved by introduction of a time-dependent pseudo-forcing function which is derived from frequency-dependent dynamic characteristics of the system by means of Hilbert transformation in the frequency domain. Surface, shallow and caisson foundation models that differed in size and depth of embedment were used. The mechanical characteristics of the systems were determined from static and forced vibration dynamic tests. An amplitude scaling technique was used for three recorded accelerograms.     

BSRs and Associated Reflections as an Indicator of Gas Hydrate and Free Gas Accumulation: An Example of Accretionary Prism and Forearc Basin System along the Nankai Trough, off Central Japan

Abstract. Multi-channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them.
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km²) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well-developed in a prism of large size. This suggests that a large prism may produce much amount of gas-bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control).
The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies (time control).
Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.     

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.     

Isotopic equilibration ages for the Miyanohara tonalite from the Higo metamorphic belt in central Kyushu, Southwest Japan: Implications for the tectonic setting during the Triassic

Abstract Miyanohara tonalite occurs in the middle part of the Higo metamorphic belt in the central Kyushu, Southwest Japan. This tonalite intrudes into early Permian Ryuhozan metamorphic rocks in the south and is intruded by Cretaceous Shiraishino granodiorite in the north. The Miyanohara tonalite yielded three mineral ages: (i) 110–100 Ma for Sm–Nd and Rb–Sr internal isochrons and for K–Ar hornblende; (ii) 183 Ma for Sm–Nd internal isochron; and (iii) 211 Ma for Sm–Nd internal isochron. The ages of 110–100 Ma may indicate cooling age due to the thermal effect of the Shiraishino granodiorite intrusion. The ages of 183 Ma and 211 Ma are consistent with timing of intrusion of the Miyanohara tonalite based on geologic constraints. The hornblende in the sample which gave 183 Ma shows discontinuous zoning under microscope, whereas the one which gave 211 Ma does not show zonal structure. These mineralogical features suggest that the 183 Ma sample has suffered severely from later tectonothermal effect compared with the 211 Ma sample. Therefore, the age of 211 Ma is regarded as near crystallization age for the Miyanohara tonalite. The magmatic process, geochronology and initial Sr and Nd isotope ratios for the Miyanohara tonalite are similar to those of early Jurassic granites from the Outer Plutonic Zone of the Hida belt that constitutes a marginal part of east Asia before the opening of the Japan Sea. Intrusion of the Miyanohara tonalite is considered to have taken place in the active continental margin during the late Triassic.     

Structurally preserved Zamites bayeri Kvaček from the Coniacian Kashima Formation (Yezo Group) of Hokkaido,Japan

A permineralized frond from the Coniacian Kashima Formation (Yezo Group) of Hokkaido, Japan, is identified as Zamites bayeri based on leaf shape, transverse orientation of stomata, papillate epidermal surface, and hollow subsurface bodies formed only on the abaxial epidermis. The specimen has an articulation at the base of the leaflet from which the leaflet was detached by means of an abscission zone. This finding suggests that Z. bayeri has compound leaves that are functionally equivalent to a twig bearing simple leaves. This functional conversion is often found in extant compound-leaved ferns or cycads growing in infertile conditions; thus Z. bayeri might have lived in a similar habitat. Leaflet articulation is also found in other Zamites species including the type species of the genus, whereas it is unknown in other bennettitalean foliar morphogenera. The rachis of the specimen has a columnar vascular bundle, which is common in bennettitalean foliage.     

On Huynen's decomposition of a Kennaugh matrix

For some special case, Huynen's decomposition cannot be used to extract a desired target from an average Kennaugh matrix. In this paper, the authors modify Huynen's method for overcoming its disadvantage, based on a simple transform of a Kennaugh matrix. Using an example, the effectiveness of the modified method is validated.     

Pan-African Alkali Granitoids from the Sør Rondane Mountains, East Antarctica

Alkali granitoids (500-550 Ma) representing a prominent Pan-African magmatic event are widely distributed in the Sør Rondane Mountains, Dronning Maud Land, East Antarctica. Geochemically, they are granitic to syenitic in composition and show an alkaline affinity of A-type granites. They are characterized by high K₂O+Na₂O (7-13 wt%) and K₂O/Na₂O (1-2), low to intermediate Mg#, wide ranges of SiO₂ (45-78 wt%), Sr (20-6500 ppm) and Ba (40-13000 ppm) and have Nb and Ti depletion in the primitive mantle normalized diagram. The granitoids are subdivided into Group I granites, Group II granites, Lunckeryggen Syenitic Complex and Mefjell Plutonic Complex. The Group I granites have higher Mg#, Sr/Ba, Sr/Y, (La/Yb)_N and LREE/HREE, lower A/CNK, SREE and initial ⁸⁷Sr/⁸⁷Sr ratios and lack Eu anomalies compared to those with negative Eu anomalies in the Group II granites. The syenitic rocks from the Mefjell Plutonic Complex are higher in alkali, Ga, Zr, Ba, and have lower Mg#, Rb, Sr, Nb, Y, F and LREE/HREE with positive Eu anomaly, whereas the granites from the Mefjell Plutonic Complex have high LREE/HREE ratios with negative Eu anomaly. The Lunckeryggen syenitic rocks have intermediate Mg#, higher K₂O, P₂O₅, TiO₂, Fe₂O₃/FeO, Ba, Sr/Y and LREE/HREE ratios with lack of Eu anomalies and are lower in Al₂O₃, Ga, Y, Nb and Rb/Sr ratios. Based on chemical characteristics combined with isotopic data, we suggest that the Lunckeryggen syenitic body and Group I granitic bodies may be derived from the mantle-derived hot basic magma by fractional crystallization with minor assimilation. We also suggest that the Group II granites may be derived from assimilation with crustal rocks to varing degrees and then fractional crystallization in higher crustal levels (ACF model). The Mefjell Plutonic Complex seems to be derived from a heterogenetic magma source compared with other granitoids from the Sør Rondane Mountains. The syenitic rocks in the Mefjell Plutonic complex have a unique source (iron-enriched) and have a chemical affinity with the charnockites in Gjelsvikjella and western Mühlig-Hofmannfjella, but not like the Yamato syenites in adjacent areas.     

Geoarchaeological studies in Nara,Japan: The integrated findings

In this article, the authors summarize 20 years of scholarship and two field projects on geoarchaeology in Nara, Japan, carried out by researchers from 12 different institutions in 4 countries. The research goal was to test an aerial photographic reconstruction of surface landforms in the Nara Basin with subsurface data. Project A was conducted at Asawa; it tested, through geological coring, whether a suspected swampy backmarsh in the eastern basin existed and whether it would yield data on the transition to wet rice agriculture in the mid‐1st millennium B.C. Project B was conducted at Miwa; it tested, through geological coring and subsequent excavation, the nature of upland agricultural terrace formation in the southeastern basin and whether the suspected existence of a 4th‐century palace site could be confirmed. Two layers of carbonaceous clay at Asawa were dated to the Early (˜5000–3500 B.C.) and Final (˜1000‐300 B.C.) phases of the Jomon period. Pollen data revealed the establishment of an evergreen oak forest from 5,000 years ago and anthropogenic changes in forest cover from 2,000 years ago. Phytoliths from rice, millets, reeds, and bamboo were recovered in layers postdating the Final Jomon carbonaceous clay. A fault scarp with anthropogenic modification of the terraces was identified at Miwa. It was discovered that an incised stream valley had been infilled in the Medieval period at the same time surface layers were razed; the front of the terrace was extended in the premodern period. Remains were recovered from the Middle Yayoi (˜100 B.C.–A.D. 100) and the Medieval (˜A.D. 1185–1603) periods. However, as the terracing involved razing the early historic levels, no data were recovered on the alleged 4th‐century palace site. The significance of these findings lies in the identification of (a) a swampy backmarsh at Asawa, where initial agricultural efforts in growing wet rice in the basin may have occurred, confirming the aerial photographic reconstruction; and (b) hillside terracing activities at Miwa, from the Medieval period onwards, which have radically changed the configuration of the natural topography. © 2005 Wiley Periodicals, Inc.     

A tripolar pattern as an internal mode of the East Asian summer monsoon

A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59?%, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.