Introduction to Hazard Assessment Flashcards
What is the coupling coefficient?
Denotes how much two plates are interacting during subduction. A coupling coefficient of 0 concerns a plate where 100% of the convergence along it is aseismic/no stress build up. A coupling coefficient of 1 concerns a plate interface which accommodates zero convergence and elastic strain builds up during the interseismic period.
What is a b-value?
The b-value determines the ratio between large and small events. An area with a high b-value shows more low magnitude events compared to high magnitude events.
How are tectonic geohazards different from geohazards?
Geohazards are more local events which are mostly weather related e.g. floods, cyclones, liquefaction, meteorites, avalanche. Tectonic geohazards are caused by internal (solid Earth) processes such as volcanic eruptions, earthquakes, tsunami, landslides.
What is natural hazard?
The potential for dangerous natural phenomena related to a natural (catastrophic) event. For example, earthquake related phenomena include ground shaking, surface rupture, soil liquefaction, and tsunami. Volcanic eruption related phenomena may include lava flows, ash falls, acid rain. Landslide phenomena may include rock/soil movement, flooding and erosion.
What is risk?
A description and measure of the potential harmful consequences of these phenomena to life, health, livelihoods, property, the economy or environment. Risk is the convolution (two functions that produce a third function) of the hazard potential with the loss potential (vulnerability). Sometimes includes exposure. Exposure consists of the elements that we value (e.g. people, assets, and the environment) that get in the way of the hazard. Vulnerability is the sensitivity of the exposed elements to the hazard (e.g. the elderly and the young,
older buildings, species at risk). Risk increases or decreases based on changes to its components. For example, climate change is causing hazards to increase in some places, thus increasing risk. On the other hand, actions that increase adaptive capacity (such as planning and preparedness activities) can decrease vulnerability, and thus, risk. Risk = Hazard potential x Loss potential
What is adaptive capacity?
Actions which increase the ability to cope with a future natural hazard. Improving adaptive capacity can decrease vulnerability and thus decrease risk. E.g. planning and preparedness activities.
What is long-term hazard assessment? Give examples.
Occurs over years-decades. Requires information on the location, size, consequences and average frequency of the hazardous event to characterise the long-term potential. This allows long-term mitigation strategies such as town zonation and infrastructure improvements to be put in place. Long-term hazard assessment is time-independent.
What is intermediate term hazard assessment? Give examples and explain the purpose.
Occurs over months-years. Focusses on how hazard varies through time around the long-term average. This is called time-dependent hazard, because it aims to establish whether hazard is higher or lower than average.
What is short-term hazard assessment? Give examples and explain the purpose.
Occurs over hours-weeks. This is done to assess whether an event is impending, and requires information to define a forecast or even prediction.
What is real time hazard assessment? Give examples and explain the purpose.
Occurs over minutes-hours. Aims to predict the extent and type of consequences as the event proceeds.
Explain the purposes of hazard assessment.
Hazard assessment enables a reduction in vulnerability to reduce the risk associated with a hazard. The type of strategy employed depends on the time scale of the event. Long-term hazard assessment involves improving the adaptive capacity through town donation and infrastructure improvement. Whereas short-term and real-time hazard assessment focus on more immediate risk - where monitoring, evacuation and emergency response might instead be used.
Define forecasting
Imprecise statement of the time, place, and ideally the nature and size of impending activity. Usually based on precursory activity and historical patterns.
Define prediction
Relatively precise statement defining a narrow spatial, temporal and magnitude window in which an event of a certain type is expected, allowing for evacuation.
What is hazard assessment?
A characterisation of the spatial and temporal distribution of likely hazardous consequences associated with a type of geohazard e.g., earthquakes, volcanic eruptions. Forecasting and prediction are two forms of hazard assessment.
Define probabilistic hazard assessment
Probability that an event of a certain size occurs in a given area and within a specific time interval and incurs specific effects (e.g. ash fall, lava flow, lahar). Probabilistic hazard assessment includes randomness in its prediction. A range of deterministic scenarios may be needed to derive a full probabilistic hazard assessment. Can therefore be calculated as the sum of the range of deterministic scenarios each weighted by its probability to occur.
