1. 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

2. 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.

3. 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

4. Note: in large earthquakes, slip on the fault initiates at the hypocenter and then propagates along the fault epicenter hypocenter fault from Tarbuck & Lutgens

5. 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

6. Types of Seismic Waves P-waves: Fastest, higher frequency. S-waves: 2nd fastest. Potentially damaging. Surface waves: Slowest. Damaging to structures. from Marshak, 2009

7. 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

8. New Zealand

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

10. Christchurch Auckland Wellington Major New Zealand Metropolitan Areas and Volcanoes

11. 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

12. New Zealand South Island Seismic Hazard From USGS

13. The Earthquake

14. Our room © Michael Bunds

15. Damage along roof line in our hotel © Michael Bunds

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

17. 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

18. So I called Danny, and he had answers! (more on what the answers were later)

19. Damage in Christchurch Major damage mostly restricted to unreinforced masonry –Some roof collapses –Collapsed walls –Collapsed facades –Chimneys –Damaged buildings: aftershock hazard Liquefaction

20. Extensively Damaged Buildings

21. © Michael Bunds

32. Source of bricks shown in previous slide

33. © Michael Bunds

37. Damaged Buildings at Risk from Aftershocks

38. © Michael Bunds

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

55. sand blow © Michael Bunds

56. sand blow © Michael Bunds

57. sand blow © Michael Bunds

58. sand blow © Michael Bunds

59. deposits from sand blows © Michael Bunds

60. sand blows © Michael Bunds

61. sand blow © Michael Bunds

62. Lateral Spread © Michael Bunds

63. Lateral Spread © Michael Bunds

64. Lateral Spread © Michael Bunds

65. Sand blow foundation damage © Michael Bunds

66. Sand blow & foundation damage © Michael Bunds

67. structural damage lateral spread © Michael Bunds

68. structural damage © Michael Bunds

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

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

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

72. 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

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

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

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

76. Surface Rupture Trace, Visited Locations, USGS and NZ Geonet Epicenters Circles mark photo locations; Mapped rupture trace in black (from GeoNet) 6 2 5 3 1 4 Christchurch

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

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

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

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

81. Aerial view of location 4 from GeoNet

82. Location 5: 4 m right lateral slip © Michael Bunds

83. Location 5: 4 m right lateral slip © Michael Bunds

84. Location 5 4 m right lateral slip © Michael Bunds

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

86. Aerial view from GeoNet

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

90. from New Zealand Geonet Aftershock Locations

91. Aftershocks 9/4 – 9/7 Aftershocks 9/7 – present From New Zealand Geonet

92. Aftershocks: Several > M w 5 Classic sequence From New Zealand Geonet

93. 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

94. approximate surface rupture trace From New Zealand Geonet

96. Comparison to Other Earthquakes Haiti Landers / Hector Mine

97. 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

98. 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

99. 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

100. 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

101. Aftershocks and areas likely to be under increased stress for right-lateral E-W faulting from King, Stein & Lin, 1994 from New Zealand Geonet

102. 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!