Characteristics of horizontal crustal deformation in Japan as deduced from frequency distribution of maximum shear strain rate

In order to study characteristics of horizontal crustal strains, we divide the Japanese Islands into 14 tectonic provinces consistent with the suggestion given byMatsuda (1990). We calculate frequency distribution of strain rates using the results of the Precise Control Survey initiated by the Geographical Survey Institute in 1973. This survey is a revision of old first- and second-order triangulation networks by trilateration. The principal axes and principal strains inside all the geodetic triangles are deduced from the comparison of the old triangulation and the new trilateration networks. The maximum shear strain rates are calculated by dividing the accumulated strains with the time intervals. The frequency distribution of strain rates is counted for each tectonic province and for the entire Japanese Islands. It is proved that the maximum shear strain rate with highest frequency ranges from 0.10–0.15 microstrain/a for 4409 data in the Japanese Islands. The mean value of the strain rates throughout the Japanese Islands is deduced to be 0.18 microstrain/a. We also calculated a mean value of strain rates for each tectonic province. Comparison is made between mean geodetic strain rates in the provinces and Quaternary strain rates estimated by geomorphic data. It is found that 0.3–0.4 microstrain/a of the highest order strain rate is now prevailing in the Izu province, the south Fossa-Magna collision zone, and some special provinces along the eastern part of the Japan Sea coast.     

Hydrological control of flooding: Tuscany,October 1992

In the study of flash-flood occurrence in small catchments the lack of flow measurements is often one of the main limiting factors. Prior to estimating the forecasting potentialities and techniques for such events, an accurate reconstruction of past event flood dynamics is first required. This issue is here addressed by analyzing, with the use of a distributed hydrological model, the hydrometeorological conditions in which a severe flash-flood occurred, on October 1992, on a 48 square kilometers catchment in the Arno basin. Such an event was caused by the persistence of intense convective clusters on the background of widespread rain bands of frontal origin. The distributed hydrological model here adopted is devoted to simulate the evolution and the variability of the primary processes involved in the runoff cycle. Together with the hydrological model structure, other particular aspects of the event reconstruction procedure are discussed: the managing and processing of the information coming from different sensors, with different temporal and spatial resolutions; the identification of local precipitation dynamics (frontal or convective) within small areas of integrated radar and rain gauges data fields; the interpolation of rain gauge data on the basis of the radar-estimated spatial correlation. The results of the distributed modeling, concerning the estimate of the flood wave at various sites, are compared with analogous results obtained with simpler lumped models.     

Seismogenic model of earthquakes in groups in tectonic block and analysis for some features of earthquake precursory field

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Numerical simulation of the detachment dynamics in North China Basin

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Elastic models of seismic failure in the Valley of Mexico

Restricted parts of the Valley of Mexico have been plagued by swarms of small earthquakes during recent years. The cause of these events is puzzling, but they may relate to massive artificial changes in the hydrology of the lake-bed which underlies most of Mexico City. If the valley responds elastically, plane strain finite element calculations can be used to relate geologic and seismic structure to observed seismicity and overall stability of the valley. These calculations show that unstable zones and areas of local seismicity coincide if the triggering mechanism of the seismicity is related to variations of pore pressure and water load.In order to make such a connection it is necessary to ascribe the generating mechanism of the seismicity to the density and elastic modulus anomalies associated with the valley structure, and to suggest that the phenomenon that triggers this seismicity is related to changes in water content of the near surface formations.     

鲜水河断裂带的构造大地测量

利用短边GPS点阵、短基线标石阵和精密激光测距 ,在与鲜水河断裂带的断层破裂带垂直的剖面上和构造盆地内进行构造大地测量 ,获得了断层软弱带和断层蠕变带上的最佳形变分布。综合利用相关地学成果和理论 ,揭示了构造形变所隐含的动力学信息 ,识别了断层应变带、塑性流变带和主断面在地面的分布范围。用外围GPS远场联测成果探讨了该断裂带的驱动力机制 ,匡正了其“左旋”运动和现今活动速度的含义。最后 ,评估了该断裂的地震活动趋势     

Hysteresis‐based flood‐wave analysis using the concept of strain

Hysteresis represents a loop in a rating curve and is a phenomenon which closely resembles that occurring in stress–strain curves used for studying the elastic properties of solid substances in engineering mechanics. Earlier hysteresis‐based studies used for defining floodwave propagation in open channels have qualitatively shown that hysteresis is an index of energy loss during floodwave propagation. Using the concept of elasticity, this paper introduces a new term called flow strain (defined as the ratio of change in discharge to the initial discharge) for investigating hysteresis. The usefulness of this new term is evaluated with use of four dam‐break studies. The study reveals that:

• 1 flow strain is a function of three wave speeds, Seddon speed, Lagrange speed, and elastic speed;
• 2 a single linear reservoir concept frequently used in flood routing is a specific variant of the Seddon speed formula;
• 3 the non‐linear storage–discharge relationship, widely used in overland flow modelling, is a variant of the kinematic wave representation;
• 4 the discharge ordinates on the recession part of a hydrograph follow a simple first‐order autoregressive form;
• 5 the hysteresis, phase difference and logarithmic decrement all define attenuation and are indices of energy loss during floodwave propagation.

Copyright © 2001 John Wiley & Sons, Ltd.     

昆仑山口西8.1级地震地表破裂参数相互关系的新认识

地震地表破裂带调查表明,昆仑山口西 8. 1级地震的破裂长度为 426km,最大水平位移6m左右,地震破裂位移的分布明显地受断层活动段控制。该次地震的破裂长度远大于统计值,文中应用地壳极限线应变的概念,通过比较中国大陆内部几次走滑型强震的地震破裂最大位移与破裂长度的关系,论述了昆仑山口西 8. 1级地震中各次级段破裂的相对独立特征,认为该次强震不是一次整体性破裂事件,而是由连续触发的几次地震组成     

Simulations of strong ground motion in SW Iberia for the 1969 February 28 (Ms= 8.0) and the 1755 November 1 (M∼ 8.5) earthquakes – II. Strong ground motion simulations

This is the second paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to use the velocity model that was proposed and validated in the companion paper for seismic intensity modelling of the 1969 ( M _s= 8.0) and 1755 ( M = 8.5–8.7) earthquakes.
First, we propose a regression to convert simulated values of Peak Ground Velocity (PGV) into Modified Mercalli Intensity (MMI) in SW Iberia, and using this regression, we build synthetic isoseismal maps for a large ( M _s= 8.0) earthquake that occurred in 1969. Based on information on the seismic source provided by various authors, we show that the velocity model effectively reproduces macroseismic observations in the whole region. We also confirm that seismic intensity distribution is very sensitive to a small number of source parameters: rupture directivity, fault strike and fault dimensions. Then, we extrapolate the method to the case of the great ( M = 8.5–8.7) 1755 earthquake, for a series of hypotheses recently proposed by three authors about the location of the epicentral region. The model involving a subduction-related rupture in the Gulf of Cádiz results in excessive ground motion in northern Morocco, suggesting that the source of the 1755 earthquake should be located further west. A rupture along the western coast of Portugal, compatible with an activation of the passive western Iberian margin, would imply a relatively low average slip, which, alone, would could not account for the large tsunami observed in the whole northern Atlantic ocean. A seismic source located below the Gorringe Bank seems the most likely since it is more efficient in reproducing the distribution of high intensities in SW Iberia due to the 1755 earthquake.