Journal of Earthquake and Tsunami

In order to determine the prospective areas of the forthcoming earthquake sources, the $b$-values of the frequency-magnitude earthquake distributions were analyzed spatially and mapped along the strike-slip fault system at the Thailand–Myanmar border. In order to constrain the relationship between the variation of $b$ and the following hazardous earthquake, the completeness of earthquake catalogue was manipulated into two datasets for (i) 1980–2000 and (ii) 1980–2005 and the $b$-values mapped. Utilizing the suitable assumption of 30 fixed earthquake events, the following $M_w\ge 5.0$ earthquakes illustrate a significant relation between their epicenter and the areas showing relatively low $b$-values. By utilizing the most recent earthquake data (1980–2015), five areas exhibiting low $b$-values (implying prospective earthquake sources) can be identified along the strike-slip fault system. Compared with earthquake activities evaluated previously along the strike-slip fault system, the data reveal that these five areas may potentially generate earthquakes up to 7.0$M_w$ within the coming 50 years; the recurrence of the $M_w$-5.0 earthquake is about 10 years and the probabilities of the $M_w$-5.0 earthquake are about 40–95%, respectively. Since these prospective hazardous seismic zones are located close to cities, population centers and hydropower dams, an effective mitigation plan should be developed.

Shear wave velocity ($V_s^{30}$) through the uppermost subsurface (30 m) is usually considered an important parameter as it dictates the dynamic behavior of soil and also acts as an input parameter for site response analysis, seismic hazard analysis, and site classification. In majority of seismically active areas across the globe, especially in developing countries like Pakistan, the $V_s^{30}$ measurements are either not available or if available, they are very limited in number to develop a seismic site-conditions map. In the absence of proper geological studies and geotechnical investigation, the slope-derived method provides a simple solution to map the site-conditions. The current study presents the development of slope-derived $V_s^{30}$ map on the basis of a correlation between $V_s^{30}$ and topographic slope for active tectonic regions and its comparison with the $V_s^{30}$ values at various locations in Pakistan. The topographic slope is calculated from digital elevation model (CDEM) of the Shuttle Radar Topography Mission (SRTM) 30 arc-sec global topographic data set. The $V_s^{30}$ values comprise of directly available, values calculated/estimated from the standard penetration tests (SPTs $N$-value) and primary waves at various locations in Pakistan. $V_s^{30}$ values at various parts/locations in Pakistan and values from the slope-derived $V_s^{30}$ map are found to be fairly comparable and based on these results for seismically active areas like Pakistan, slope-derived method can be applied for the first-order site-condition studies.

An analytical solution for diffraction of both plane and cylindrical SH waves induced by a horseshoe shaped cavity with an inverted arch is presented in this paper. The geometry of the cavity is assumed to be composed of two circular arcs. By introducing an auxiliary boundary, the whole physical region is divided into two computational regions. The scattered wavefield in the open region and the standing wavefield in the enclosed region are presented by means of the wave function expansion method. Both of the wavefields are given in terms of the wave function series with unknown coefficients. By applying the Graf’s addition formula, two systems of equations for seeking the unknowns are derived by taking advantage of the boundary conditions based on the region-matching strategy. The problem of wave scattering is finally solved after seeking the solutions of the two systems of equations through standard matrix techniques. Then the effects of the excitation frequency, the cavity embedment depth and cavity geometry are discussed. The differences in terms of ground motions under different excitations and the influence of source location under cylindrical waves are also examined.

When a tsunami reaches a shore, it propagates along river channels with tremendous energy and overtops river levees. It causes severe damage to the levee structures through scouring along levee slope. In the present study, gully scours created along the levee slopes of two rivers (Omotogawa and Sakarigawa Rivers) in Iwate Prefecture and three rivers (Nanakitagawa, New Kitakamigawa, and Abukumagawa Rivers) in Miyagi Prefecture were investigated after the 2011 Great East Japan tsunami. The energy head during levee overtopping for each location was calculated from post-tsunami surveys. The relationship between the energy head and gully scour dimensions (length, width, and depth) was analyzed. The analyses clarified that gully scour dimensions were greatly dominated by two important phenomena: (i) overflow type (free overflow or submerged overflow), and (ii) soil texture at the scoured region. The present study results can be utilized to obtain the overtopping flow height for post-tsunami analysis.

Numerical simulation is an important measure to study the seismic performance of buckling-restrained braced frames (BRBFs). Practically, some simplified models, such as the elastic–plastic with kinematic hardening model and the elastic perfectly-plastic model, are used to simulate the behavior of buckling-restrained brace (BRBs). To provide structural engineers the reference of errors when simplified models are used, this paper comparatively evaluates the effect of the BRB model on seismic structural responses using the OpenSees software. A comparison is made on six-storey and 16-storey BRBFs with rigid beam-to-column connections; these are designed according to Chinese seismic design code. Moreover, the effects of the post-yielding stiffness ratio of frame $\alpha$ and the stiffness ratio of BRB to frame $\beta$ on the errors are specifically investigated through a parametric study of both BRBFs. The results show that the seismic response average errors of the simplified models are mostly less than 5%, which satisfies the engineering requirements.

In order to ensure structural safety and integrity in earthquake conditions, it may be useful or even necessary to increase the seismic safety of the highway embankments with reinforcement inclusions. The inclusion of geosynthetics in highway embankments may provide an additional tensile strength and durability to construct more stable and earthquake resistant embankments. In this study, the contributions of the primary factors as inclusion of the geotextile reinforcement, slope inclination and dynamic motion characteristics affecting the seismic performance of the highway embankments are evaluated. Shake table models of the unreinforced and geosynthetic reinforced highway embankments with different slope inclinations are designed. An extensive series of shake table tests were performed under dynamic motions with different predominant frequencies. Test results revealed that inclusion of geotextiles in the embankment model causes deamplification of the transmitted accelerations traveling through the reinforced embankment models. Thus, the geosynthetic reinforcement successfully enhances the seismic performance and mitigates earthquake-related hazards. Contribution of this study to the literature is that the efficiency of the geosynthetic reinforcement by means of energy absorption properties is highly dependent on the dynamic motion characteristics but less dependent to the degree of slope inclination.