Evaluation of the damping modification factor for structures subjected to near-fault ground motions

The damping modification factor (DMF) has been extensively used in earthquake engineering to describe the variation of structural responses due to varied damping ratios. It is known that DMFs are dependent not only on structural dynamic properties but also on characteristics of ground motions. DMFs regulated in current seismic codes are generally developed based on far-fault ground motions and are inappropriately used in structural design where pulse-like near-fault ground motions are involved. In this paper, statistical investigation of the DMF is performed based on 50 carefully selected pulse-like near-fault ground motions. It is observed that DMFs for pulse-like ground motions exhibit significant dependence on the pulse period T _p in a specific period range. If the period of the structure in response is close to the pulse period, the DMF attains the same level as that derived from far-fault ground motions; as the period of the structure is considerably larger or smaller than the pulse period T _p , the response reduction effect by the increased damping ratio is generally small, except for large earthquakes with long pulse periods, which exhibit significant reduction of response for structures with periods smaller than T _p . Based on the statistical results of DMFs, the empirical formulas for estimating DMFs for displacement, velocity and acceleration spectra are proposed, the effect of structural period, pulse period and damping ratio are considered in the formulas, and the formulas are designed to satisfy the specific reliability requirement in the period range of 0.1 < T/T _p  < 1, which is of engineering interest.     

LiDAR-derived DEM evaluation of deep-seated landslides in a steep and rocky region of Japan

In steep and rocky terrains, their rough surfaces make it difficult to create landslide inventories even with detailed maps/images produced from airborne LiDAR data. To provide objective clues in locating deep-seated landslides, the surface textures of a 5 km² steepland area in Japan was investigated using the eigenvalue ratio and slope filters calculated from a very high resolution LiDAR-derived DEM. The range of filter values was determined for each of a number of surface features mapped in the field and these included: cracked bedrock outcrops, coarse colluvial deposits, gently undulating surfaces, and smooth surfaces. Recently active slides commonly contained patches of ground in which deposition and erosion occurred together near the erosion front, or where cracked bedrock outcrops and coarse colluvial deposits coexisted under a gently undulating surface. The characteristic eigenvalue and slope filter values representing this sliding process were applied to maps of the DEM derived filter values to extract potential sites of recent landslide activity. In addition, the relationships between the filter values of deep-seated landslides at various stages of evolution within the field mapped area were extended to the entire study area, to assess the contribution that landslide evolution makes to change in the landscape as a whole. While landslide components made up the steepest as well as the gentlest parts of the landscape depending on their evolutionary stage, landslides were constantly coarsened and steepened by progressive erosion, probably initiated by river bank erosion at the foot of slopes.     

Damping identification of a full‐scale passively controlled five‐story steel building structure

A series of large‐scale dynamic tests was conducted on a passively controlled five‐story steel building on the E‐Defense shaking table facility in Japan to accumulate knowledge of realistic seismic behavior of passively controlled structures. The specimen was tested by repeatedly inserting and replacing each of four damper types, that is, the buckling restrained braces, viscous dampers, oil dampers, and viscoelastic dampers. Finally, the bare steel moment frame was tested after removing all dampers. A variety of excitations was applied to the specimen, including white noise, various levels of seismic motion, and shaker excitation. System identification was implemented to extract dynamic properties of the specimen from the recorded floor acceleration data. Damping characteristics of the specimen were identified. In addition, simplified estimations of the supplemental damping ratios provided by added dampers were presented to provide insight into understanding the damping characteristics of the specimen. It is shown that damping ratios for the specimen equipped with velocity‐dependent dampers decreased obviously with the increasing order of modes, exhibiting frequency dependency. Damping ratios for the specimen equipped with oil and viscoelastic dampers remained constant regardless of vibration amplitudes, whereas those for the specimen equipped with viscous dampers increased obviously with an increase in vibration amplitudes because of the viscosity nonlinearity of the dampers. In very small‐amplitude vibrations, viscous and oil dampers provided much lower supplemental damping than the standard, whereas viscoelastic dampers could be very efficient. Copyright © 2012 John Wiley & Sons, Ltd.     

Geochemical Features of Vein Anhydrite from the Kakkonda Geothermal System, Northeast Japan

Abstract. Cathodoluminescence (CL) color, rare earth element (REE) content, sulfur and oxygen isotopes and fluid inclusions of anhydrite, which frequently filled in hydrothermal veins in the Kakkonda geothermal system, were investigated to elucidate the spatial, temporal and genetical evolution of fluids in the deep reservoir. The anhydrite samples studied are classified into four types based on CL colors and REE contents: type-N (no color), type-G (green color), type-T (tan color) and type-S (tan color with a high REE content). In the shallow reservoir, only type-N anhydrite is observed. In the deep reservoir, type-G anhydrite occurs in vertical veins whereas type-T and -N in lateral veins. Type-S anhydrite occurs in the heat-source Kakkonda Granite. The CL textures revealed that type-G anhydrite deposited earlier than type-T in the deep reservoir, implying that fracture system was changed from predominantly vertical to lateral.
Studies of fluid inclusions and δ³⁴S and δ¹⁸O values of the samples indicate that type-N anhydrite deposited from diluted fluids derived from meteoric water, whereas type-G, -T and -S anhydrites deposited from magmatic brines derived from the Kakkonda Granite with the exception of some of type-G with recrystallization texture and no primary fluid inclusion, which deposited from fossil seawater preserved in the sedimentary rocks. Type-G, -T and -S anhydrites exhibit remarkably different chondrite-normalized REE patterns with a positive Eu anomaly, with a convex shape (peak at Sm or Eu) and with a negative Eu anomaly, respectively. The difference in the patterns might result from the different extent of hydrothermal alteration of the reservoir rocks and contribution of the magmatic fluids.     

Mercury dynamic simulation of Minamata Bay by using a three-dimensional numerical model

Ocean Dynamics - Residual mercury dynamic has been the research emphasis since mercury contamination was publicly recognized in Minamata Bay. Simulation of mercury distribution and transport...     

Warm water intrusion from the Kuroshio into the coastal areas south of Japan

Sea surface temperature (SST) has been measured in the south of Japan using a thermometer set up in the ferry boat to investigate the characteristics of the warm water intrudes into the coastal areas from the Kuroshio. Time series analysis was applied to the SST data with satellite images and hydrographic observation data from April 1987 to September 1989. The results indicate that the warm Kuroshio water intruded into the coastal areas on the Enshu-nada and the Kumano-nada Seas intermittently with periods of about 50 and 20 days associated with the fluctuation of the Kuroshio path and the Kuroshio frontal disturbance respectively. The intrusion with a 50-day period was dominant when the Kuroshio took a stationary small meander path (B- and C-types). The warm water spread to the west at 20 cm s^–1, and was estimated to have a depth of 150 m at least and supply enough heat to make up the loss due to the evaporation in the coastal area. During the straight path of the Kuroshio, it was detected that the warm water intruded into coastal areas only with a 20-day period. The warm water that intrudes with a period of 20 days spreads to the west at 25 cm s^–1 in a small scale.