Abstract
Regional earthquake early warning (EEW) alerts and related risk-mitigation actions are often triggered when the expected value of a ground-motion intensity measure (IM), computed from real-time magnitude and source location estimates, exceeds a predefined critical IM threshold. However, the shaking experienced in mid- to high-rise buildings may be significantly different from that on the ground, which could lead to sub-optimal decision-making (i.e., increased occurrences of false and missed EEW alarms) with the aforementioned strategy. This study facilitates an important advancement in EEW decision-support, by developing empirical models that directly relate earthquake source parameters to resulting approximate responses in multistory buildings. The proposed models can leverage real-time earthquake information provided by a regional EEW system, to provide rapid predictions of structure-specific engineering demand parameters that can be used to more accurately determine whether or not an alert is triggered. We use a simplified continuum building model consisting of a flexural/shear beam combination and vary its parameters to capture a wide range of deformation modes in different building types. We analyse the approximate responses for the building model variations, using Italian accelerometric data and corresponding source parameter information from 54 earthquakes. The resulting empirical prediction equations are incorporated in a real-time Bayesian framework that can be used for building-specific EEW applications, such as (1) early warning of floor-shaking sensed by occupants; and (2) elevator control. Finally, we demonstrate the improvement in EEW alert accuracy that can be achieved using the proposed models.
Highlights
Earthquake early warning (EEW) typically involves (1) detecting earthquakes in the early stages of fault rupture; (2) rapidly predicting the intensity of the impending shaking at selected target sites; and (3) issuing alerts to end users that trigger important risk-mitigation actions before the arrival of the potentially damaging seismic motions (Allen and Melgar 2019)
We develop empirical equations that directly relate the approximate building responses of Sect. 2.1 to earthquake source parameters that can be rapidly estimated with a regional EEW algorithm, and site-specific soil characteristics
We provide a simple demonstration of the improvement in alert accuracy offered by making decisions to trigger EEW alarms based on engineering demand parameters (EDPs) instead of intensity measure (IM)
Summary
Earthquake early warning (EEW) typically involves (1) detecting earthquakes in the early stages of fault rupture; (2) rapidly predicting the intensity of the impending shaking at selected target sites (or across regions); and (3) issuing alerts to end users that trigger important risk-mitigation actions before the arrival of the potentially damaging seismic motions (Allen and Melgar 2019). These systems generally carry out step (2) of EEW by leveraging information provided in the early portion of near-fault seismic signals (e.g., 3–4 s of P- and/or S-waves) to determine source parameter estimates, which are used to predict resulting ground-motion intensity measures (IMs) at distant sites (e.g., Cremen and Galasso 2020) The uncertainty of this process may be captured by applying the well-known probabilistic seismic hazard analysis (PSHA; Cornell 1968) framework in real-time (i.e., RTPSHA; e.g., Iervolino et al 2006; Convertito et al 2008), as follows: fIM( | ) = ∫m ∫r f ( |m, r)fM(m| )fR(r| ) dm dr (1).
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