earthquakes (1) john townend eqc fellow in seismic studies [email protected] cotton 520, ph....
TRANSCRIPT
Earthquakes (1)
John Townend
EQC Fellow in Seismic Studies
Cotton 520, ph. 463-5411
Outline
What have we seen in the last couple of years? What is an earthquake? How do we observe earthquakes scientifically? How do we describe earthquakes?
Our home
Colours represent peak ground acceleration expected at 10% probability in 50 years
Figure courtesy of GNS Science
What is listening near Christchurch?
Seismographs
Satellite radar interferogram spanning the 22 February Christchurch earthquake. Image provided by the Centre for the Observation and Modelling of Earthquakes,
Volcanoes and Tectonics (COMET+) .
What else is watching?
Greendale fault → Darfield EQ
United States Geological Survey (USGS)
Big fleas have little fleas...
A day-long record of seismic activity recorded at McQueen’s Valley (western Banks Peninsula) almost one month after the M6.3 Christchurch earthquake. Image provided by GeoNet.
And they keep biting
A day-long record of seismic activity recorded at McQueen’s Valley (western Banks Peninsula) twelve months after the M6.3 Christchurch earthquake. Image provided by GeoNet.
0 20 40 60 80 100 120 140 160 180 2000
50
100
150
200
250
300
350
Time since 4 September Darfield earthquake (in days)
Rat
e of
aft
ersh
ocks
(i.e
. nu
mbe
r of
ear
thqu
akes
per
day
)
The rate of aftershock activity generally decreases with time...
0 20 40 60 80 100 120 140 160 180 2000
50
100
150
200
250
300
350
Time since 4 September Darfield earthquake (in days)
Rat
e of
aft
ersh
ocks
(i.e
. nu
mbe
r of
ear
thqu
akes
per
day
)
But there can be surprises...
1 2 3 4 5 6 7 810
0
101
102
103
104
Magnitude
Num
ber
of la
rger
ear
thqu
akes
For every large earthquake there are many little ones...
1 2 3 4 5 6 7 810
0
101
102
103
104
Magnitude
Num
ber
of la
rger
ear
thqu
akes
But size isn’t everything...
Stacy Squires/The Press
Carys Monteath/The Press
Ground accelerations
Figures provided by GNS Science/GeoNet — see RSNZ/PMSAC briefing for further details
東日本大震災 , 11 March 2011
The earth rings like a bell
Regional deformation
Preliminary GPS displacement data (version 0.1) provided by the ARIA team at JPL and Caltech. All Original GEONET RINEX data provided to Caltech by the Geospatial Information Authority (GSI) of Japan.
Animated version
Expected tsunami wave heights across the Pacific basin computed by the National Oceanic and Atmospheric Administration (NOAA) Center for Tsunami Research.
Tsunami
Tsunami propagation
A tsunami travels over the abyssal plain (d~5.5 km) at a velocity of ~235 m s–1 (~850 km hr–1).
Why such a big tsunami?
Ide et al.,2011, Science
Sato et al.,2011, Science
Kodaira et al., JAMSTEC
Why such a big tsunami?
What are all these waves?
The P and S waves travel through the Earth’s
interior and lose energy (attenuate) faster than the Rayleigh surface waves
Where to with early warnings?
A public warning was issued 8 s after seismic waves were first detected, 31 s after rupture started (27 bullet trains stopped)
Magnitude underestimated, meaning ground motions and tsunami heights were also underestimated
Suggested reading material Geosystems (8th ed.), Christopherson
Chapter 12, especially p. 338–343, 349–355 Chapter 16, p. 466–472
Earthshaking science: what we know (and don't know) about earthquakes, Hough
Predicting the unpredictable, Hough Caught in the crunch, Ansell and Taber Magnitude eight plus, Grapes
Online resources GeoNet
http://www.geonet.org.nz
United States Geological Survey http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/
Earthquake Research Institute, University of Tokyo http://outreach.eri.u-tokyo.ac.jp/eqvolc/201103_tohoku/eng
GEO Geohazards Supersite http://supersites.earthobservations.org/honshu.php
Geospatial Information Authority of Japan http://www.gsi.go.jp/cais/topic110313-index-e.html
Seismological Laboratory, Harvard University http://seismology.harvard.edu/research_japan.html
UNAVCO http://www.unavco.org/community_science/science_highlights/2011/M8.9-Japan.html
Quake-safeing
Chimneys Water cylinders Foundations Roof tiles Solid fuel stoves Bookcases
And who has an earthquake kit
prepared?