earthquakes (1) john townend eqc fellow in seismic studies john.townend@vuw.ac.nz cotton 520, ph....

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Earthquakes (1)

John Townend

EQC Fellow in Seismic Studies

john.townend@vuw.ac.nz

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?

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