非海相双壳类江西蛤（Jiangxiella）首次发现于日本

首次报道日本西南部发现的晚三叠世非海相双壳类江西蛤（Jiangxiella)，并讨论这一发现的意义。认为原产于湘、赣、粤地区的江西蛤是地理分布极有限的土著属，它在日本西南部的发现表明当时该区与华南东部的古地理关系极为密切，可能原属同一地块。     

Study on basement structures of the northeast Pamirs

1 Geologic setting and layout of the DSS observation network In the studied area there are three major tectonic units, which are referred to as Tianshan fold system, Tarim basin and West Kunlun fold system (Bureau of Geology and Mineral Resources of Xinjiang Uygur Autonomous Region, 1993). The Tianshan fold system is a polycyclic geosyncline on the north edge of Tarim basin, and an orogenic zone resulting from collision and convergence between Tarim block and the Junggar-North Tianshan…     

Magma Mingling/mixing vs. Magmatic Fractionation: Geneses of the Shirakawa Mo-mineralized Granitoids, Central Japan

Abstract. Leucocratic biotite granites are main components in the Hatogaya pluton and the Hirase stock in the Shirakawa region of central Japan. Molybdenite‐quartz vein mineralizations are widespread in and around the Hatogaya pluton and the Hirase stock, in which the largest is vein swarm of the Hirase mine. Mafic enclaves occur abundantly with granitic to granodi‐oritic matrix in the northern part of the Hatogaya pluton, while they are rare in the Hirase granitic stock. The enclaves with generally round shape have mostly diabasic to fine plutonic textures under the microscope, and show interfingering and lobate contacts with the felsic matrix. The enclaves are quartz monzodiorite in composition containing SiO>₂ mostly around 60 %. They have felsic blebs, thus are considered a mingled magma of basaltic compositions originated in depth and a felsic magma generated from the Hida metamorphic‐plutonic complexes or their basement. The mingled magma further mixed with and reacted with the felsic magma with SiO₂ 70 %, and then formed granodiorite‐granite of the high Na group (Na₂O higher than 4.25 %). Thus, compositional variation of the northern part of the Hatogaya pluton was caused by the magma mingling. The mingling happened to be deeper level produced homogeneous granodiorite of the Mihoro pluton. Biotite granite of the low Na group (less than 4.25 %) could have originated in a granitic magma generated also from the Hida metamorphic‐plutonic complexes or their basement. Most of the granites, occurring in the southern part of the Hatogaya pluton and Hirase stock, show high Rb/Sr ratio, strong Eu negative anomalies and flat REE patterns, and are thus considered as fractionated products of the SiO₂ 70 % original magma. The strong concentration of molybdenum in the Hirase stock can be explained by high degree of magmatic fractionation which produced MoS₂‐rich residual melts, suitable fractures developed at the latest Cretaceous time, and preservation of the mineralized fractures at the present level of erosion.     

Lower crustal fluid distribution in the northeastern Japan arc revealed by high-resolution 3D seismic tomography

The Ou Backbone Range strikes northwards through the central northeastern Japan arc and is bounded on both sides by the active reverse Uwandaira and Sen'ya faults. We have applied a traveltime inversion method (seismic tomography) with spatial velocity correlation to active and passive seismic data in order to investigate a three-dimensional (3-D) velocity structure. The data set contains 33,993 P- and 18,483 S-wave arrivals from 706 natural sources and 40 blasts, as well as 2803 P-wave traveltime data from 10 explosions detonated during the 1997 controlled source experiment. The traveltime inversion reveals a zone beneath the Ou Backbone Range in which P-wave velocities (V_P) are approximately 6–8% lower than the average velocity at equivalent depths. The low V_P and a low V_P to S-wave velocity (V_S) ratio (V_P/V_S) of about 1.65 suggest the presence of aqueous fluids in the middle crust.     

Active right-lateral strike-slip fault zone along the southern margin of the Japan Sea

We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north.     

Distribution Functions of Tsunami Wave Heights

The problem of describing the distribution functions of tsunami wave heights is discussed. Data on runup heights obtained in field surveys of several tsunamis for the last decade are used to calculate the empirical distribution functions. It is shown that the log-normal distribution describes the observed data well. This means that the irregular topography and coastline are major factors which influence the height distribution. The power distribution related with the geometric decay of the propagated wave is a good approximation for one event (Sulawesi, January 1, 1996) only. Results of a numerical simulation of the tsunami event in the Japan (East) Sea on July 12, 1993 are presented. It is shown that the computed wave height distribution, obtained by using the runup correction in the framework of nonlinear shallow-water theory, is in good agreement with the observed height distribution. Simulations are used to study the transformation of the distribution function on different distances from the source.     

多阶段构造地貌的水系统计特征——以山东半岛东北部为例

通过对胶东半岛水系分枝状况的空间展布、主要河流中的河长分形计算 ,以及水库高程统计分析 ,反映了山东半岛东北部地区的水系统计特征与多阶段新构造抬升活动的相关关系。     

Pyroclastic flows from the 1991 eruption of Unzen volcano,Japan

Pyroclastic flows from Unzen were generated by gravitational collapse of the growing lava dome. As soon as the parental lobe failed at the edge of the dome, spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris. The flows had a overhanging, tongue-like head and cone- or rollershaped vortices expanding outward and upward. Most of the flows traveled from 1 to 3 km, but some flows reached more than 4 km, burning houses and killing people in the evacuated zone of Kita-kamikoba on the eastern foot of the volcano. The velocities of the flows ranged from 15 to 25 m/s on the gentle middle flank. Observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud. The basal avalanche swept down a topographic low and formed to tongue-like lobe having well-defined levees; it is presumed to have moved as a non-Newtonian fluid. The measured velocities and runout distances of the flows can be matched to a Bingham model for the basal avalanche by the addition of turbulent resistance. The rheologic model parameters for the 29 May flow are as follows: the density is 1300 kg/m³, the yield strength is 850 Pa, the viscosity is 90 Pa s, and the thickness of the avalanche is 2 m. The ash cloud is interpreted as a turbulent mixing layer above the basal avalanche. The buoyant portions of the cloud produced ash-fall deposits, whereas the dense portions moved as a surge separated from the parental avalanche. The ash-cloud surges formed a wide devastated zone covered by very thin debris. The initial velocities of the 3 June surges, when they detached from avalanches, are determined by the runout distance and the angle of the energy-line slope. A comparison between the estimated velocities of the 3 June avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path, detached directly from the turbulent heads of the avalanches. The over-running surge that reached Kita-Kamikoba had an estimated velocity higher than that of the avalanche; this farther-travelled surge is presumed to have been generated by collapse of a rising ash-cloud plume.