Earthquake Science (Seismology)

Seismometers and seismic networks Seismometers and seismic networks Earthquake aftershocks Earthquake aftershocks Earthquake hazard maps Earthquake hazard maps Earthquake prediction Earthquake prediction

Seismometers Sensitive devices for measuring ground motion Measures either vertical or horizontal (E-W or N-S) motion Smaller units used in exploration are called geophones

Some seismograph Stations in Canada (see

Station SILO - deployed by helicopter

POLARIS research project at UWO

An earthquake which follows a larger earthquake (or main shock) and originates at or near the focus of the larger earthquake. Generally, major earthquakes are followed by a larger number of aftershocks, decreasing in frequency with time. The aftershock sequence can persist for months or years following a major earthquake. Aftershock!

Kobe earthquake - aftershocks The aftershock distribution can be used to map the extent of fault rupture.

Earthquake Hazard Maps 4 Based on calculated probability of earthquake ground motion 4 Used by engineers for building codes

Global Seismic Hazard Map Peak ground acceleration (pga) with a 10% chance of exceedance in 50 years %g Hazard Level (%g) Low: 0-8% Moderate: 8-24% High: 24-40% Extreme: > 40% ?

Canadian Seismic Hazard Map

Earthquake Prediction “If I were a brilliant scientist, I would be working on earthquake prediction.” … Los Angeles radio talk show I heard just after the Northridge earthquake of January 17, 1994.

Earthquake prediction - methods A section of fault that has not produced a significant amount of smaller earthquakes is a likely candidate for a large earthquake. 1. The seismic gap hypothesis

Earthquake prediction - methods Forecasting earthquakes by estimating the average time between large events on a fault. The data for such a study can be found by digging trenches across fault lines. 2. Earthquake recurrence interval

Example of earthquake prediction by recurrence interval: California Parkfield earthquake experiment

Earthquake prediction - methods Stress changes from an earthquake can increase earthquake probability elsewhere 3. Earthquake stress triggering

Stein et al., 1997 “12% probability for a large event south of the major western port city of Izmit in the next 30 years” Example of earthquake prediction by stress triggering: Turkey

Earthquake prediction - methods Foreshock (rare) Strange animal behaviour Unusual electrical signals Changes in water wells Radon gas release 4. Precursory phenomena