Risk, Hazard & Resilience

Expected Annual Loss (EAL) is the average loss that a structure, portfolio, or region is expected to incur per year from seismic events, computed by integrating the loss curve over all possible hazard levels. It is a fundamental metric for risk-informed decision-making and insurance pricing.

Exposure is the inventory of people, buildings, infrastructure, and economic assets located in an area subject to seismic hazard. It is one of the three fundamental components of seismic risk, alongside hazard and vulnerability, and it determines who and what is at stake.

A hazard curve is a graphical representation of the annual probability of exceeding different levels of ground shaking at a site, produced by probabilistic seismic hazard analysis. It provides the fundamental input for probabilistic risk assessment, insurance pricing, and performance-based design.

Loss estimation is the process of quantifying the expected consequences of earthquakes — in terms of repair costs, casualties, downtime, and economic disruption — by combining hazard, exposure, and vulnerability models. It provides the quantitative basis for risk-informed decision-making.

Probabilistic Seismic Hazard Analysis (PSHA) is a methodology that estimates the probability of exceeding a given level of ground shaking at a site within a specified time period, accounting for all possible earthquake scenarios and their associated uncertainties. It is the foundation of modern seismic design codes and risk assessment.

Resilience is the ability of a community, system, or structure to prepare for, absorb, recover from, and adapt to disruptive events such as earthquakes. It encompasses both the reduction of damage during an event and the speed and effectiveness of recovery afterward.

The return period is the average time between occurrences of an event of a given or greater magnitude, expressed as the inverse of its annual probability of exceedance. In earthquake engineering, it is used to characterize seismic hazard levels and to define design earthquakes.

Seismic risk is the potential for loss — in lives, property, economic activity, or functionality — resulting from the interaction of seismic hazard, exposure, and vulnerability. It is distinct from seismic hazard, which describes the physical phenomenon alone, and is the quantity that risk mitigation seeks to reduce.

Vulnerability is the susceptibility of people, buildings, or systems to damage or loss when exposed to a hazard of a given intensity. It is a fundamental component of seismic risk, alongside hazard and exposure, and is the primary target of retrofit and mitigation efforts.

A lifeline is a critical infrastructure system — such as water, power, transportation, communications, or healthcare — whose continued functioning is essential to emergency response, public health, and community recovery after an earthquake. Lifeline resilience is a central concern in seismic risk reduction.