Velázquez Ortíz, Omar Alejandro; (2021) Investigating the cross-disciplinary components of earthquake early warning systems. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Earthquake early warning (EEW) systems typically provide early estimates of earthquake magnitude, hypocentre location and/or ground-shaking estimates, as well as alerts ranging from a few seconds to tens of seconds, before the arrival of the damaging ground shaking at a target site. The warnings provided by these systems allow for the implementation of fast protection actions carried out by individuals like ‘drop, cover, and hold-on’, or the evacuation of buildings if the lead time is long enough. Nevertheless, the information and warning time provided by an EEW system could also be used by earthquake engineers as EEW seems to bear a powerful potential for the automatic activation of protection measures for infrastructure and critical systems, aiming at the reduction of risk due to earthquakes. Such automatic actions may include stopping elevators at the nearest floor, opening firehouse doors, slowing rapid-transit vehicles and high-speed trains to avoid accidents, to mention some. Few are the attempts found in literature about engineering applicability of EEW. This scarcity might be related to the fact that the real-time estimation of earthquake source parameters contains considerable uncertainty that may lead to potential economic losses if false or missed alarms are not avoided. However, different state-of-the-art studies regarding decision-making procedures for EEW have suggested more reliable approaches that can potentially reduce the uncertainty in the estimates provided by the system (e.g., earthquake source parameters and ground shaking), reducing the probability of triggering missed/false alarms, and therefore minimising the expected losses. The potential of designing new real-time advanced building protection applications for EEW is the motivation of this thesis. Mainly, two applications are considered: 1) Design of controlled structural systems using the early warning information, particularly, the use of semi-active devices denominated magnetorheological dampers. A control algorithm that governs the behaviour of the dampers is calibrated to obtain the most favourable response of a benchmark structure equipped with one damper. The results reveal that the developed EEW-based control algorithm can effectively reduce the expected loss of the considered case-study structure. 2) Prediction of shaking demands that can be expected in mid-rise to high-rise buildings, using a simplified continuum building model. A series of illustrative examples show how the newly developed prediction models can be efficiently used, in a Bayesian framework, for building-specific EEW applications based on the (acceleration) response in buildings, such as a) early warning of floor-shaking sensed by occupants; and b) control of elevator in buildings. The progress of technology and advances in the scientific understanding of engineering and seismology have promoted the rapid development of EEW systems around the world. However, their effectiveness is often limited as they lack the integration between their technical and social components. This thesis also aims at filling this gap to investigate which measures could be needed to increase the organisational resilience of local community stakeholders and the private sector. This topic is explored by implementing a mixed-method approach on the case study Mexico City (Mexico), that can be considered an area at risk due to the combination of high seismic hazard, structural and social vulnerabilities. This thesis shows the promising applicability of engineered applications of EEW systems and suggests a robust framework for the integration of the technical and societal components of EEW.

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