Presentation on theme: "M w 7.1 Canterbury, New Zealand Earthquake Michael Bunds Department of Earth Science Utah Valley University and Laura Benninger U.S. Bureau of Reclamation."— Presentation transcript:
M w 7.1 Canterbury, New Zealand Earthquake Michael Bunds Department of Earth Science Utah Valley University and Laura Benninger U.S. Bureau of Reclamation
Copyright 2010, Michael P. Bunds, all rights reserved This material may be used for educational purposes only. Users agree to acknowledge the original author and the Department of Earth Science, Utah Valley University when using any original portion of this material.
What is an Earthquake? Ground shaking caused by a sudden release of energy within Earth. Most result from slip on a fault. from Marshak, 2009
Note: in large earthquakes, slip on the fault initiates at the hypocenter and then propagates along the fault epicenter hypocenter fault from Tarbuck & Lutgens
Types of Faults Strike-slip faults; San Andreas fault Normal fault; Wasatch fault is an example Thrust faults; common at convergent plate boundaries from Marshak, 2009
Types of Seismic Waves P-waves: Fastest, higher frequency. S-waves: 2nd fastest. Potentially damaging. Surface waves: Slowest. Damaging to structures. from Marshak, 2009
Seismogram P-waves arrive first, followed by S then surface waves Delay between arrival of different wave types increases with distance from the earthquake from Tarbuck & Lutgens
So What the Just Happened? Was it the Alpine fault? –Might be able to generate the shaking, but should have been more rolling, longer lasting Marlborough fault system? Maybe? Faults too small + distant? ???? Something else? Solution: –Cell network was still up! (but $25/mb, eeegads) –Danny Horns had already emailed me 23 minutes after the earthquake! Christchurch Alpine fault Marlborough fault system North Island fault system Pacific plate Australian plate
So I called Danny, and he had answers! (more on what the answers were later)
Damage in Christchurch Major damage mostly restricted to unreinforced masonry –Some roof collapses –Collapsed walls –Collapsed facades –Chimneys –Damaged buildings: aftershock hazard Liquefaction
Aftershocks 9/4 – 9/7 Aftershocks 9/7 – present From New Zealand Geonet
Aftershocks: Several > M w 5 Classic sequence From New Zealand Geonet
Shaking Intensities Measured as Mercalli Magnitude and/or peak ground acceleration (pga) Christchurch generally MM VI to VIII (strong to severe; pga 0.2 to 0.4 g) Up to MM IX, 1.2 g pga near fault rupture Good strong motion data collected
approximate surface rupture trace From New Zealand Geonet
Comparison to Other Earthquakes Haiti Landers / Hector Mine
Shaking Intensity and damage from Haiti Earthquake 3.5 million people exposed to MM VII – IX shaking Many buildings vulnerable to earthquake damage Port au Prince From USGS
Comparison to Haiti Earthquake Both earthquakes had similar magnitudes, proximities to cities Huge loss of life (~230,000) vs. no lives loss –Higher population density in Haiti; greater shaking intensity –Much more resistant buildings in Christchurch –Time of day (4:53 pm vs. 4:35 am) –Good building codes and retrofitting buildings saves lives Haiti earthquake on or near recognized fault, Canterbury earthquake on previously unknown fault –We are good at identifying hazardous faults, and there is lots of work to do
Comparison to Landers Earthquake Landers: M w 7.3, 1992, remote So. Cal. desert Landers & Canterbury earthquakes were on little-known faults with very long recurrence interval (10,000 + years) Both were complex, (probably) resulting from several shorter fault segments rupturing in rapid succession Landers was followed 7 years later by Hector Mine event (M w 7.1) –Raises concern of future earthquakes in the area From USGS
Aftershocks 9/4 – 9/7 Aftershocks 9/7 – present Regional stress changes caused by slip on a fault. Red indicates increased stress for right lateral faulting From New Zealand Geonet from King, Stein & Lin, 1994
Aftershocks and areas likely to be under increased stress for right-lateral E-W faulting from King, Stein & Lin, 1994 from New Zealand Geonet
Conclusions and Lessons We are good at identifying hazardous faults, but lots of work needs to be done Preparations –Proper building construction and retrofitting works –Good community preparation counts (infrastructure, insurance, responders) During and immediately after an earthquake –Don’t run outside – duck and cover –Leave building as soon as you can –Remain aware of surroundings after the event – don’t stand next to buildings, especially brick buildings – aftershocks happen!
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