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

New Zealand

For those of you accustomed to looking at the Earth upside-down

Christchurch Auckland Wellington Major New Zealand Metropolitan Areas and Volcanoes

Kermadec Trench Christchurch Auckland Wellington Hikurangi Trench Puysegur Trench 3.1 cm/yr 5.4 cm/yr Alpine fault Marlborough fault system North Island fault system M 7.1 9/4/10 Pacific plate Australian plate Kermadec trench New Zealand Plate Tectonic Setting

New Zealand South Island Seismic Hazard From USGS

The Earthquake

Our room © Michael Bunds

Damage along roof line in our hotel © Michael Bunds

Interior wall cracking in our hotel © Michael Bunds We learned later that the hotel had been reinforced for earthquake safety in 2004

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 ed 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

Extensively Damaged Buildings

© Michael Bunds

Source of bricks shown in previous slide

© Michael Bunds

Damaged Buildings at Risk from Aftershocks

© Michael Bunds

Liquefaction Water-saturated sediment is liquified by shaking Sand blows (also called sand volcanoes) Lateral spread Substantial damage to structures, sewers, storm drains, roadways

sand blow © Michael Bunds

sand blow © Michael Bunds

sand blow © Michael Bunds

sand blow © Michael Bunds

deposits from sand blows © Michael Bunds

sand blows © Michael Bunds

sand blow © Michael Bunds

Lateral Spread © Michael Bunds

Lateral Spread © Michael Bunds

Lateral Spread © Michael Bunds

Sand blow foundation damage © Michael Bunds

Sand blow & foundation damage © Michael Bunds

structural damage lateral spread © Michael Bunds

structural damage © Michael Bunds

Geology & Geophysics of the Earthquake Seismicity Surface rupture Aftershocks Shaking intensities Comparison to other earthquakes

Seismogram from day of event recorded at station near Christchurch main event aftershocks from New Zealand Geonet

Seismogram of Event Complex – multiple pulses of energy? from New Zealand Geonet

Focal Mechanism Right lateral strike-slip on E-W fault or left lateral on N-S fault Rt. Lat. On E-W was more likely based on regional geology T P modified from USGS

USGS & GeoNet Epicenters Used for Surface Rupture Search Christchurch USGS GeoNet

Location 2: 4 m right-lateral slip; negligible north down dip slip © Michael Bunds

Surface Rupture Distributed en echelon shears Riedel shears right-lateral slip + minor north-side down Probably extends to at least 10 – 12 km depth

Surface Rupture Trace, Visited Locations, USGS and NZ Geonet Epicenters Circles mark photo locations; Mapped rupture trace in black (from GeoNet) Christchurch

Location 2: 4 m right-lateral slip; negligible north down dip slip © Michael Bunds

Location 2: 4 m right lateral slip; negligible north down dip slip © Michael Bunds

Location 4: Pressure ridge, 4 m right lateral slip © Michael Bunds

Location 4: Extended fence; pressure ridge; Reidel shears; 4 m right lateral slip © Michael Bunds

Aerial view of location 4 from GeoNet

Location 5: 4 m right lateral slip © Michael Bunds

Location 5: 4 m right lateral slip © Michael Bunds

Location 5 4 m right lateral slip © Michael Bunds

Location 6: ~2.5 m right lateral slip; approaching western limit of surface rupture © Michael Bunds

Aerial view from GeoNet

R R’ P Riedel Shears Experiment: clay cake over cut wood Earthquake: unfaulted sediment & soil over bedrock Aerial view from GeoNet

from New Zealand Geonet Aftershock Locations

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!