earthquake science (seismology). seismometers and seismic networks seismometers and seismic networks...

EarthquakEarthquake Sciencee Science

(Seismology)(Seismology)

• Seismometers and seismic Seismometers and seismic networks networks

• Earthquake aftershocks Earthquake aftershocks

• Earthquake hazard mapsEarthquake hazard maps

• Earthquake predictionEarthquake 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 www.polarisnet.ca)

Station SILO - deployed by helicopter

www.polarisnet.ca

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

Based on calculated probability of earthquake ground motion

Used by engineers for building codes

Global Seismic Hazard Map

Peak ground acceleration (pga) with a 10% chance of exceedance in 50 years

80 24 40%g

Hazard Level (%g)

Low: 0-8%Moderate: 8-24%High: 24-40%Extreme: > 40%

?

http://www.seismo.ethz.ch/GSHAP/global/global.html

Canadian Seismic Hazard Map

http://www.pgc.nrcan.gc.ca/seismo/eqhaz/seishaz.htm

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

http://faculty.weber.edu/bdattilo/shknbk/notes/erthqkprdctn.htm

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

http://faculty.weber.edu/bdattilo/shknbk/notes/erthqkprdctn.htm

Example of earthquake prediction by recurrence interval: California

Parkfield earthquake experiment

http://quake.wr.usgs.gov/research/parkfield/

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