2: How Faults Rupture and Earthquake Hazards Flashcards
What are the three stages of the Elastic Rebound Theory?
Accumulation of stress, friction prevents slip (elastic deformation, strain), stress exceeds strength of rock and causes a rupture, releasing the stress.
The largest aftershock tends to be how much smaller than the main earthquake?
1 unit of magnitude
How soon after does the largest aftershock tend to occur?
few hours to days
What is the general pattern of aftershocks?
diminish with time after the main event
Give an example of a seismic gap
Loma Prieta, San Andreas – 1989, M~7
What is a stress shadow?
A period of earthquake inactivity after a large earthquake has released tension.
Give an example of a stress shadow with specific magnitudes: Date/Mag/Fault, period of shadow, Date/Mag/Fault of next big EQ.
7.8Mw in 1906 on San Andreas fault, no earthquakes larger than Mw6 for 73 years (except 1 in 1911 of 6.5). 1979 (Mw6.0) pre-shocks to Loma Prieta began.
Around __% of earthquakes occur at depths of >__km. Such earthquakes tend to occur in ___-____ zones.
25%, >60km, Wadati-Benioff zones
Name three distinctive features of a deep earthquake
Weak/absent surface waves, less attenuation of body waves, far fewer aftershocks.
Why does simple brittle failure or “elastic rebound theory” occur in deep earthquakes?
Temperature too high
Name three possible rupture mechanisms in deep earthquakes
Dehydration embrittlement, shear instability and local stress-induced melting, transformational faulting
What is a typical velocity of a rupturing fault?
~2-4km/s
Explain the rupture process, including origin and results
Origin at focus, ruptures along fault plane, generating seismic waves along entire fault plane
Knowing L = S x T, how can we determine the length of the rupture?
Know speed and time of rupture from seismogram triangulation.
Give an example of a “sub-event” in a rupture process
Regions on fault plane where slip was concentrated compared to regions where there was little or no slip – asperities.
