Numerical Simulation of the 1918 Puerto Rico Tsunami

The Caribbean Sea region is well known for its hurricanes, and less known for tsunamis. As part of its responsibilities in hazard assessment and mitigation, the U.S.A. Federal Emergency Management Agency, and the Puerto Rico Civil Defense, funded a pilot study to perform a numerical simulation of the 1918 Puerto Rico tsunami, one of the most deadly in the region. As part of the study a review has been made of the tectonic and tsunamigenic environment around Puerto Rico, the fault parameters for the 1918 event have been estimated, and a numerical simulation has been done using a tsunami propagation and runup model obtained through the Tsunami Inundation Modeling for Exchange (TIME) program. Model results have been compared with the observed runup values all along the west coast of Puerto Rico.     

Seismic parameters controlling far-field tsunami amplitudes: A review

We present a review of the influence of various parameters of the sources of major oceanic earthquakes on the amplitude of tsunamis at transoceanic distances. We base our computations on the normal mode formalism, applied to realistic Earth models, but interpret our principal results in the simpler framework of Haskell theory in the case of a water layer over a Poisson half-space. Our results show that source depth and focal geometry play only a limited role in controlling the amplitude of the tsunami; their combined influence reaches at most 1 order of magnitude down to a depth of 150 km into the hard rock. More important are the effects of directivity due to rupture propagation along the fault, which for large earthquakes can result in a ten-fold decrease in tsunami amplitude by destructive interference, and the possibility of enhanced tsunami excitation in material with weaker elastic properties, such as sedimentary layers. Modelling of the so-called tsunami earthquakes suggests that an event for which 10% of the moment release takes place in sediments generates a tsunami 10 times larger than its seismic moment would suggest. We also investigate the properties of non-double couple sources and find that their relative excitation of tsunamis and Rayleigh waves is in general comparable to that of regular seismic sources. In particular, landslides involving weak sediments could result in very large tsunamis. Finally, we emphasize that the final amplitude at a receiving shore can be strongly affected by focusing and defocusing effects, due to variations in bathymetry along the path of the tsunami.     

The frictional behavior of lizardite and antigorite serpentinites: Experiments,constitutive models,and implications for natural faults

Laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults. We have conducted friction experiments on antigorite and lizardite serpentinites, rocks common to both continental and oceanic crustal faults. We conducted both velocity-step tests and timed-hold tests on bare surfaces and gouge layers of serpentinite at room temperature. We find that the coefficient of friction of lizardite serpentinite is quite low (0.15–0.35) and could explain the apparent low stresses observed on crustal transform faults, while that of antigorite serpentinite is comparable to other crustal rocks (0.50–0.85). The frictional behavior of both types of serpentinite is well described by a two-mechanism model combining state-variable-dominated behavior at high slip velocities and flow-dominated behavior at low velocities. The two-mechanism model is supported by data from velocity-step tests and timed-hold tests. The low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite.     

广东省强震台网建设概况

本文论述了广东省强震台网建设的目的和原则,介绍了台网中使用的强震仪,收取的强震记录和处理情况、台网管理及其展望。     

Group Strong Earthquakes and Triggering by Tidal Stress

The results obtained using the group model of earthquakes generated in tectonic blocks are fur ther used in this paper to analyze the relationship between the Ms ≥ 7.0 events in Chinese ma inland and the modulation and triggering from the earth tides. The research shows that the Ms 7.0 events in Chinese mainland have been significantly triggered by the tidal stress, especially within the active period with group strong earthquakes. In the quiescence period of strong earthquakes, no Ms7.0 events were triggered, while within the active period, over 82.4% of strong earthquakes took place within a special moon phase, which is 36.4 % higher than the average. Therefore, the modulation and triggering of tidal stress can be used to distinguish the active periods and to forecast the time of the strong earthquakes within the active period. The relationship between the tidal triggering and the tectonic dynamic condition is investigated and the mechanism of the modulation is simulated with the group model of earthquakes generated in tectonic blocks.     

Inelastic buildings with tuned mass dampers under moderate ground motions from distant earthquakes

The effectiveness of tuned mass dampers (TMD) in vibration control of buildings was investigated under moderate ground shaking caused by long‐distance earthquakes with frequency contents resembling the 1985 Mexico City (SCT) or the 1995 Bangkok ground motion. The elastic–perfectly plastic material behaviour was assumed for the main structure, with linear TMDs employed by virtue of their simplicity and robustness. The accumulated hysteretic energy dissipation affected by TMD was examined, and the ratio of the hysteretic energy absorption in the structure with TMD to that without it is proposed to be used, in conjunction with the peak displacement ratio, as a supplementary TMD performance index since it gives an indication of the accumulated damage induced in the inelastic structures. For the ground motions considered, TMD would be effective in reducing the hysteretic energy absorption demand in the critical storeys for buildings in the 1.8–2.8 s range. The consequence is reduction in damage of the buildings which would otherwise suffer heavy damage in the absence of TMD, resulting in economical restorability in the damage control limit state. This is of practical significance in view of the current trend toward performance‐based design. Copyright © 2001 John Wiley & Sons, Ltd.