Areas Of High Seismic Risk Research Articles

Optical fibre sensors for earth sciences:: from basic concepts to optimising glass composition for high temperature applications

This paper reviews the technical evolution of optical fibre sensors relevant to earth sciences with particular reference to high temperature measurements. Optimisation of fibre composition and system design to fully realise the potential of these sensors has led to the substantial advances in both distributed and point sensor systems. Applications of these sensors in the field of earth sciences are discussed to provide a deeper understanding of the potential for monitoring geodynamical and chemical processes in areas of high seismic and volcanic risk.

Lessons of the 25 January 1999 Earthquake in Central Colombia

On January 25, 1999, an earthquake of magnitude ML = 6.1 occurred in central Colombia, which caused 1,200 deaths, 5,000 injuries, more than 250,000 people affected and economic losses estimated at US$1.2 billion. The earthquake left some important lessons that must be taken into account for the management of similar situations in the future. With respect to the behavior of buildings, the soundness and importance of the code of practice for buildings was demonstrated as a tool for the prevention of seismic disasters. The management of the emergency in cities such as Pereira and Armenia showed the need for planning, continued preparedness and mitigation awareness. The importance of the Colombian Prevention and Disaster Attention System (SNPAD) was demonstrated although the need to enhance organizational aspects, citizen awareness and participation was made evident. The characteristics of the disaster reflect a typical situation that can occur in many Latin American cities located in areas of high seismic risk. This article presents the main lessons learned from this event in the light of work performed by the research team for natural disasters from the Department of Civil and Environmental Engineering of the Universidad de Los Andes.

Seismic behavior of a high-strength concrete framed tube

An integrated analytical/experimental study is conducted to investigate the use of high-strength concrete (8 000–10 000 psi) in high-rise framed tube structural systems located in areas of high seismic risk. Results indicate that displacement demands from recorded strong ground motions are less than that which can be supplied by critical beam-to-column joints in the designed structure. Furthermore, the structural system offers high lateral stiffness, high redundancy and high energy dissipation through well-distributed plastic hinging in the spandrel girders. © 1997 John Wiley & Sons, Ltd.

A Note on the Relationship Between a Sedimentary Basin's Basement Topography and the Damage Pattern of Earthquakes: Chaos and Order

The phenomenon of localized resonance in sedimentary basins with irregular basement topography (Rial et al. , 1992) was recently independently confirmed by Moczo et al. (1996) in a numerical study that shows how a single, concave upwards trough in the basement of an otherwise horizontal layer of sediment overlying rock can give rise to localized resonance. In an effort to complement these studies this note turns to the opposite effect: localized de-amplification, as created by a convex section of the sediment/rock interface. It is shown here that de-amplification is indeed localized, being strongest directly above convexities in the basement whereby seismic risk should be substantially reduced. Further, it is found that even a small increase in topographic height of a convex segment of the sediment/rock interface can produce orders of magnitude decrease (nonlinear de-amplification) in ground motion amplitude at the site directly above it, especially if the contrast in elastic impedances between bedrock and sediment is high. Thus, it becomes possible, at least theoretically, to identify areas that will stand safe, as it is to identify areas of high seismic risk, provided the topography of the basement is known.

Statistical analysis of strong-motion accelerograms and its application to earthquake early-warning systems

SUMMARY In view of increasing damage due to earthquakes, and the current problems of earthquake prediction, real-time warning of strong ground motion is attracting more interest. In principle, it allows short-term warning of earthquakes while they are occurring. With warning times of up to tens of seconds it is possible to send alerts to potential areas of strong shaking before the arrival of the seismic waves and to mitigate the damage, but only if the seismic source parameters are determined rapidly. The major problem of an early-warning system is the real-time estimation of the earthquake’s size. We investigated digitized strong-motion accelerograms from 244 earthquakes that occurred in North and Central America between 1940 and 1986 to find out whether their initial portions reflected the size of the ongoing earthquake. Applying conventional methods of time-series analyses we calculate appropriate signal parameters and describe their uncertainties in relation to the magnitude and epicentral distance. The study reveals that the magnitude of an earthquake can be predicted from the first second of a single accelerogram within f 1.36 magnitude units. The uncertainty can be reduced to about f0.5 magnitude units if a larger number (2 8) of accelerograms are available, which requires a dense network of seismic stations in areas of high seismic risk.

Seismology Demonstrations and Activities for Inservice Training of K-12 Teachers in Areas of High Seismic Risk

The Island of Hawaii is the site of frequent, destructive earthquakes. To prepare local teachers and students for these events, demonstrations and activities were developed to explain the origin, distribution, and history of earthquakes in Hawaii. Topics include plastic and brittle behavior, strength of materials, energy and energy waves, seismometers and seismograms, magnitude and intensity, temporal and spatial distribution of earthquakes, and the causes of earthquakes in Hawaii. These demonstrations and activities are applicable to other areas of high seismic risk with a few modifications to account for local geology.

Radon in soil anomaly observed at Los Azufres geothermal field, Michoacan: a possible precursor of the 1985 Mexico earthquake (Ms = 8.1)

A radon anomaly in a nuclear track detector placed on a fault was detected prior to the destructive (Ms = 8.1) Mexican earthquake of 19 September 1985. The fault is a structural feature of the geothermal field ‘Los Azufres’, 260 km NE of the epicentral area. Since no other phenomenon can be found as a possible cause for the radon anomaly, it is proposed that preseismic regional stress perturbations may produce changes in the fluid transport patterns at the fault, suggesting that radon measurements in similar conditions could provide a good precursor in high seismic risk areas.

A Critical Review of the Seismic Design Provisions for Ductile Shear Walls of the Canadian Code and Commentary

The 1975 Canadian Building Code for the design of reinforced concrete shear wall buildings in high seismic risk areas includes provisions that are new and significant. This paper critically examines some of these provisions, especially as they apply to cantilever shear walls. Clarifications in the definitions of curvature, member, and system ductilities are attempted. The relationship between curvature and system ductility is examined. Code provisions on allowable shear stress in the wall in the plastic hinge region and the provisions for the classification of the walls are discussed. Attention of the designer is drawn to some aspects of the code and the commentary that may result in structures of doubtful safety.