Bending-related faulting of the incoming oceanic plate and its effect on lithospheric hydration and seismicity: A passive and active seismological study offshore Maule,Chile

We have studied the dependency between incoming plate structure, bending-related faulting, lithospheric hydration, and outer rise seismic activity offshore Maule, Chile. We derived a 2D Poisson's ratio distribution from P- and S-wave seismic wide angle data collected in the trench-outer rise. High values of Poisson's ratio in the uppermost mantle suggest that the oceanic lithosphere is highly hydrated due to the water infiltration through bending-related normal faults outcropping at the seafloor. This process is presumably facilitated by the presence of a seamount in the area. We conclude that water infiltrates deep into the lithosphere, when it approaches the Chile trench, producing a reduction of crustal and upper mantle velocities, supporting serpentinization of the upper mantle. Further, we observed a mantle Vp anisotropy of 8%, with the fast velocity axis running normal to the abyssal hill fabric and hence in spreading direction, indicating that outer rise processes have yet not affected anisotropy.The first weeks following the megatrust Mw = 8.8 Maule earthquake in 2010 were characterized by a sudden increase of the outer rise seismic activity, located between 34° S and 35°30′ S. We concluded that this phenomenon is a result of an intensification of the water infiltration process in the outer rise, presumably triggered by the main shock, whose epicenter was located some 100 km to the south east of the cluster.     

The interpretation of culture in nature: Landscape transformation and vegetation change during two centuries at Hystad,SW Norway

In Norway, on-site biological surveys precede the designation of nature reserves. Although many nature conservation areas have been affected by past human use (e.g. cattle grazing, timber harvesting), a typical biological survey may fail to portray the extent of human influence on biodiversity and vegetation dynamics. In 1984, Hystad forest (western Norway) was made a nature reserve after botanists interpreted the ecosystem 'close to untouched'. It was thought best to leave the forest alone, so no management plan was developed. It was later realized that the vegetation was changing, but the reason was not obvious. I gathered and analyzed further biological data plus information on land-use history from varied sources (e.g. cadastral maps, archive material and oral histories). The area has undergone a series of transformations since the 17th century. The present forest is no more than 100 years old, and extensive parts are much younger. The initial survey underestimated the extent of cultural impact and failed to predict vegetation change subsequent to reserve establishment, whereas a historical-geographical approach reveals that the vegetation is in a state of transition, driven primarily by a change from active farming to farm abandonment. Planning for conservation must recognize past as well as present human use of the landscape to anticipate consequent land cover responses.     

Capability of the penetrator seismometer system for lunar seismic event observation

We developed a seismometer system for a hard landing “penetrator” probe in the course of the former Japanese LUNAR-A project to deploy new seismic stations on the Moon. The penetrator seismometer system (PSS) consists of two short-period sensor components, a two-axis gimbal mechanism for orientation, and measurement electronics. To carry out seismic observations on the Moon using the penetrator, the seismometer system has to function properly in a lunar environment after a hard landing (impact acceleration of about 8000 G), and requires a signal-to-noise ratio to detect lunar seismic events. We evaluated whether the PSS could satisfactorily observe seismic events on the Moon by investigating the frequency response, noise level, and response to ground motion of our instrument in a simulated lunar environment after a simulated impact test. Our results indicate that the newly developed seismometer system can function properly after impact and is sensitive enough to detect seismic events on the Moon. Using this PSS, new seismic data from the Moon can be obtained during future lunar missions.     

Probabilistic Estimation of Hazard on Engineering Site Based on the Intensity of Historic Earthquakes and A Preliminary Comparison with Seismic Hazard Analysis

This paper introduces a new method to estimate the seismic hazard on engineering site.The method is mainly based on intensity data of historical earthquakes.The obvious feature of the method is to use some ideas of seismic hazard analysis and considering regional seismicity tendency.The authors depict the comprehensive method to estimate the related parameters and predict the seismic hazards for 14 sites as practical examples.Some problems are also discussed.Compared with seismic hazard analysis,this method has certain advantages,such as simpler computation,lower uncertainty and smaller sensitivity factor.Moreover total hazard P(I≥i)of a site can be examined with real historic data.The result given by the method in this paper can be more stable than that given by seismic hazard analysis nowadays.     

沙漠历史地理学的几个理论问题--以我国河西走廊历史上的沙漠化研究为例

干旱地区的沙漠化主要发生在内陆河流下游,沙漠化过程的途径主要有就地起沙、风蚀绿洲、流沙入侵、洪积物掩埋绿洲４种,前两者最重要。由于绿洲水资源的移动和重新分布而导致绿洲的转移过程,并不一定意味着绿洲的缩小或消失;只要大的气候环流形势和流域的总水量无大变化,则其绿洲总面积就不致发生大的改观,沙漠化土地在一定条件下是可以逆转的。     

中美青藏高原数字宽频带地震观测

1991年7月至1992年7月,中美合作在青藏高原进行了天然地震观测。布设了由11个台站组成的台阵,其中7个台站由北至南分布在青藏公路格尔木至拉萨段沿线,2个分别在其两侧,另外2个在青藏高原东部。此台阵使用REF TEK 72A-02记录器和宽频带STS-2地震计,进行事件触发及连续记录。此次观测为在青藏高原内采集地震数据提供了极好的机会。     

Seismicity in subduction zones from local and regional network observations

The data provided by local and regional seismograph networks are essential for the solution of many problems of subduction-zone seismology. The capabilities of such networks are limited by the instrumentation currently in common use and the unfavorable source-station geometry often imposed by the regional geography. Nevertheless, important contributions have come from the data gathered in many of the earth's subduction zones. The accuracy of hypocenter locations based on regional data is affected by the complex velocity structures characteristic of subduction zones, but the problems are now well-understood. Examples of numerous studies of the spatial configurations of the seismicity in subduction zones and consequent interpretations of seismogenesis and subduction processes are reviewed. Studies of the distributions of earthquakes in time and with magnitude, for events down to the microearthquake level, have the potential for clarifying the earthquake-generating processes and, possibly, a basis for earthquake prediction. Other uses of local and regional network data have been for investigations of coda-Q and the identification of asperities in subduction zones.