Abstract Seismic performances of Lexington Dam during the 1989 Loma Prieta earthquake are assessed. Linear and nonlinear analyses are used to identify locations of tension zones where cracks are likely to occur. Numerical analyses are for longitudinal and transverse sections of the dam. Assessments of natural vibration characteristics of the dam are based on numerical simulation of geophysical and forced vibration testing procedures. Nonlinear analyses are based on equivalent linear and elastoplastic solution procedures. The acronyms of computer programs used are SHAKE, SHAKEM and FLAC. Analyses procedures and computer programs used are commonly used in dam engineering practice. Relative movements of observers representing onsite accelerometers are included. The information presented is expected to be of interest to engineers and seismologists in dam engineering practice.

Abstract The tectonic stress regime of the Caribbean region has been studied by stress tensor inversion analysis for the area bounded by Latitudes 17.32o to 23.79o N and Longitudes 81.47o to -60.56o E. A total of two hundred and twenty (220) fault plane solutions (FPS), made up of the seismic (earthquake) events that have occurred in the region of the study were found on the data catalog of the project website of the global centroid moment tensor, were employed in this study. To characterize the stress regimes of the region of study, the classification of the region based on the global moment tensor project is as follows: Cuba-zone, Haiti-zone, Dominican-republic, Monapassage, Puerto Rico, Virgin-Island and the Leeward Island. The gravity geophysical method revealed the presence of multiple or swarms of fractured lines within the same geographical range of study which might have developed over the years as a result of the interaction and coupling effect of the plate boundaries that have close proximity to the region of study. The seismicity pattern indicates that none of the provinces or countries located within the Caribbean region is devoid of large-magnitude earthquake occurrences capable of wreaking severe havoc on the immediate environment. Obviously, our stress tensor inversion result indicates two types of stress regimes namely compression and the strike-slip with different orientations. Cuba-zone, Haiti-zone, Dominican Republic, Monapassage, and Leeward Island are governed mainly by compression stress regimes. In contrast, the strike-slip stress regimes mainly govern the Puerto Rico and the Virgin Island.

Abstract Looking for electromagnetic effects of earthquakes, pulse signals are detected preceding the moment of the event or following it. The advance or delay is from 0 s to 200 s. The signals are observed as single or pair pulses in the frequency range 0-5 Hz. Dynamical spectra of the signals are presented and their characteristics are discussed. The signals impact actively on the magnetosphere and ionosphere. As a result of such impact a sharp change in the regime of geomagnetic pulsation excitation may occur. The detected response of the pulsations is considered and analyzed.

Abstract Rainfall-induced landslides stand as the prevailing geohazard in tropical and subtropical regions. The ongoing global climatic changes have introduced a wave of anomalous rainfall events across the world. These abnormal weather patterns have triggered numerous landslide incidents, resulting in significant loss of life and property. To develop early warning systems for such threats to people in mountainous areas of Chittagong, Bangladesh, it requires an in-depth understanding of the geo-environmental properties of soil slopes under heavy rainfall. Historical records reveal that rainfall in total exceeding 150–250 mm has resulted in both localized slope collapses and debris floods. When it rains heavily, rainwater infiltrates initially unsaturated slopes, elevating the degree of saturation while decreasing soil suction. Consequently, the reduced shear strength along the critical slip surface diminishes the factor of safety (FoS), and slope failure occurs. As a result, studies of soil-water characteristics have been conducted, followed by laboratory testing at the impacted sites, and the study found that rainfall and soil type (fine-grained silt) were the most critical factors behind landslides. The mechanism of slope failure is also demonstrated using a simple numerical infiltration model and a slope stability equation. The soil characteristics, the saturated volumetric water content (θs), closely match the field water holding capacity (θf), with a minor difference of 4-8%, and the drainage condition at the bottom of the slope appear to be important factors. Application of these test results to an early warning system for landslides and flash floods is finally demonstrated based on some simplifying assumptions.

Abstract Bangladesh has encountered a serious and recurring threat from earthquakes. The goal of this study is to determine how much earthquake awareness there is among students nationwide. Our initial objective is to provide an overview of the earthquake risks Bangladesh is prone to, including discussions of previous seismic events and any recently identified threats or scientific advancements. Then, analysis was done with the information collected through survey. The analysis reveals a range of outcomes, from encouraging results to unsettling possibilities. Fifty percent of people have clear idea regarding earthquake and fifty percent people are doubtful on the earthquake issue. Furthermore, though eighty six percent people have idea what to do during earthquake but fourteen percent people have no idea what to do during earthquake. The survey and the result show a variety of outcome. The awareness regarding the earthquake preparedness has increased significantly but not up to the mark. More activities should be implemented for the achievement of the awareness level.