Archive for December, 2008

December 22, 2008

Gisborne 20/12/2007 M6.6Mw and aftershocks

20/12/2007 Mag 6.7ML (6.6Mw)

Public ID: 2839343
Lat/Long: -38.8901, 178.537
Date/Time UTC: 20/12/2007 07:55:17
(NZ Daylight Time): Thursday, 20 December 2007 at 8:55 pm
Depth: 33 km
No. of Phases used: 48
Status: reviewed
Location: Tuahenui Bank, offshore East of Gisborne, N.I. (geonet)
Maximum Intensity: MM 8
Energy Released: 169,203.1003 tonnes of TNT
Casualties: None
.
While the earthquake was initially reported to have caused no deaths, an elderly woman in Gisborne suffered a heart attack and died shortly after the quake.

A number of buildings in central Gisborne were damaged. The central business district was closed off to allow building inspectors to assess buildings for damage; three buildings had collapsed. There were blackouts immediately after the earthquake hit. The town clock stopped at 8:55pm.
Three buildings collapsed in the central business district of Gisborne, and severe structural damage occurred to others. Casualties would have resulted if the quake had occurred a few hours earlier when many people were on the streets. Aside from the severe damage in Gisborne, small items (eg. glassware, ornaments, books) toppled and fell off shelves in many locations including Gisborne, Hawke’s Bay, Bay of Plenty, Palmerston North, and Wellington. Contents were ejected from cupboards in Gisborne, Hawke’s Bay, Bay of Plenty, and Wellington. Small appliances and furniture (eg. TVs) slid a lot or fell over in Gisborne, Hawke’s Bay, Bay of Plenty, Paraparaumu, and Wellington, and large appliances and furniture fell over in Gisborne. Electricity was affected in Gisborne and Napier, and other infrastructure such as gas, telephone, internet, water and sewage were also affected in Gisborne. Broken crockery and glassware were reported in Gisborne and Wairoa. Building damage such as damage to chimneys, broken windows and cracks in exterior walls was reported from Gisborne and Wairoa, and severely distorted buildings and totally collapsed walls were reported in Gisborne.
The cost of the damage is expected to be $16-30 million.

GCMT MTS

GCMT MTS GISBORNE NZ 6.8MW 20-12-2007

.
Strong motion data show very high amplitude acceleration records around 0.2g at three locations (reaching 0.28g in Gisborne city). Recordings in Gisborne city also revealed a predominant displacement direction, parallel to the main street where most of the damage occurred.
The main event was followed by sparse aftershocks consistent with a rupture of the subducted plate, with the largest aftershock of magnitude 4.6 occurring on December 22nd.
GPS data recorded by continuous GPS instruments have also shown that slow slip occurred after the main shock. The slow slip was triggered on the subduction interface, rather than on the same fault plane as the aftershocks.
This event started on about the same day as the earthquake and proceeded in a manner similar to past slow slip events in the same region. The slip region was north of the earthquake but seemed to abut the aftershock
zone. The slow slip lasted about 57 days with faster moment release in the beginning and then tailing off. The average slip was about 120 mm over an area of 2,450km2. The moment of the slow slip was 1.17 x1019 Nm = 6.65Mw.
This is the first clear-cut case worldwide of triggered slow slip.

IRIS Global Displacement Wavefields

click on thumb for full size image
IRIS GDF GISBORNE NZ 6.8MW 20-12-2007

6.7ML location (geonet)

Networks estimates of location

aftershock maps

Data is based on polygon search area Latitude -38.5 to -39.0, Longitude 177.70 to 178.95. Some events may fall outside the borders of the map, especially to the West and the East, so you may need to zoom out to see these.
After the initial 1 hour map, the “ghost” or opaque icons shown on the maps are previous events to the time period shown at the top of the map, to show the cumulative pattern of the aftershocks which can be helpful in determining the extent of the Fault that failed.

aftershock maps 4 hour period

6.7 aftershocks map – (0-1hr)

summary

mag1= 0 , mag2= 7 , mag3= 16
mag4= 0 , mag5= 0 , mag6= 1
total= 24
new energy released= 25.07 TTNT
total energy released= 169,228.17 TTNT

6.7 aftershocks map – (1-4hrs)

summary

mag1= 2 , mag2= 31 , mag3= 10
mag4= 0 , mag5= 0 , mag6= 0
total= 43
new energy released= 18.89 TTNT
total energy released= 169,247.06 TTNT

6.7 aftershocks map – (4-8hr)

summary

mag1= 5 , mag2= 16 , mag3= 4
mag4= 0 , mag5= 0 , mag6= 0
total= 25
new energy released= 11.42 TTNT
total energy released= 169,258.48 TTNT

6.7 aftershocks map – (8-12hrs)

summary

mag1= 1 , mag2= 15 , mag3= 2
mag4= 1 , mag5= 0 , mag6= 0
total= 19
new energy released= 52.92 TTNT
total energy released= 169,311.40 TTNT

6.7 aftershocks map – (12-16hr)

summary

mag1= 0 , mag2= 8 , mag3= 1
mag4= 0 , mag5= 0 , mag6= 0
total= 9
new energy released= 1.84 TTNT
total energy released= 169,313.23 TTNT

6.7 aftershocks map – (16-20hrs)

summary

mag1= 0 , mag2= 9 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 11
new energy released= 2.90 TTNT
total energy released= 169,316.14 TTNT

6.7 aftershocks map – (20-24hr)

summary

mag1= 0 , mag2= 7 , mag3= 0
mag4= 0 , mag5= 0 , mag6= 0
total= 7
new energy released= 1.40 TTNT
total energy released= 169,317.53 TTNT

6.7 a/s map – (24hrs cumulative)

summary

mag1= 8 , mag2= 93 , mag3= 35
mag4= 1 , mag5= 0 , mag6= 1
total= 138
total energy released= 169,317.53 TTNT

aftershock maps 12 hour period

6.7 aftershocks map – (24-36hrs)

summary

mag1= 1 , mag2= 19 , mag3= 1
mag4= 0 , mag5= 0 , mag6= 0
total= 21
new energy released= 2.52 TTNT
total energy released= 169,320.05 TTNT

6.7 aftershocks map – (36-48hrs)

summary

mag1= 1 , mag2= 28 , mag3= 4
mag4= 1 , mag5= 0 , mag6= 0
total= 34
new energy released= 117.69 TTNT
total energy released= 169,437.75 TTNT

6.7 aftershocks map – (48-60hrs)

summary

mag1= 3 , mag2= 43 , mag3= 5
mag4= 1 , mag5= 0 , mag6= 0
total= 52
new energy released= 120.48 TTNT
total energy released= 169,558.23 TTNT

6.7 aftershocks map – (60-72hrs)

summary

mag1= 0 , mag2= 5 , mag3= 7
mag4= 0 , mag5= 0 , mag6= 0
total= 12
new energy released= 28.81 TTNT
total energy released= 169,587.04 TTNT

72hr timeline graph

Gisborne 6.7ML 2007 72hr aftershock Timeline Graphclick on image for full size version, opens in new tab/window

aftershock maps 24 hour period

6.7 a/s map – 3-4 days (72-96hr)

summary

mag1= 0 , mag2= 18 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 20
new energy released= 5.67 TTNT
total energy released= 169,592.72 TTNT

6.7 a/s map – 4-5 days (96-120hrs)

summary

mag1= 1 , mag2= 19 , mag3= 0
mag4= 0 , mag5= 0 , mag6= 0
total= 20
new energy released= 2.86 TTNT
total energy released= 169,595.57 TTNT

6.7 a/s map – 5-6 days(120-144hrs)

summary

mag1= 2 , mag2= 14 , mag3= 0
mag4= 0 , mag5= 0 , mag6= 0
total= 16
new energy released= 1.17 TTNT
total energy released= 169,596.74 TTNT

6.7 a/s map – 6-7days (144-168hrs)

summary

mag1= 2 , mag2= 6 , mag3= 1
mag4= 0 , mag5= 0 , mag6= 0
total= 9
new energy released= 1.89 TTNT
total energy released= 169,598.63 TTNT

7 day (168hrs) timeline graph

Gisborne 6.7ML 2007 7 day aftershock Timeline Graphclick on image for full size version, opens in new tab/window
.

aftershock maps 7 day period

a/s map – 1-2 weeks (168-336hrs)

summary

mag1= 6 , mag2= 40 , mag3= 7
mag4= 0 , mag5= 0 , mag6= 0
total= 53
new energy released= 18.50 TTNT
total energy released= 169,617.13 TTNT

a/s map – 2-3 weeks (336-504hrs)

summary

mag1= 4 , mag2= 40 , mag3= 3
mag4= 0 , mag5= 0 , mag6= 0
total= 47
new energy released= 6.62 TTNT
total energy released= 169,605.25 TTNT

a/s map – 3-4 weeks (504-672)

summary

mag1= 3 , mag2= 30 , mag3= 4
mag4= 1 , mag5= 0 , mag6= 0
total= 38
new energy released= 23.13 TTNT
total energy released= 169,621.76 TTNT

a/s map – 4-5 weeks (672-840hrs)

summary

mag1= 0 , mag2= 9 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 11
new energy released= 2.30 TTNT
total energy released= 169,600.93 TTNT

a/s map – 5-6 weeks (840-1008hrs)

summary

mag1= 1 , mag2= 17 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 20
new energy released= 8.80 TTNT
total energy released= 169,607.43 TTNT

a/s map – 6-7 weeks (1008-1176)

summary

mag1= 0 , mag2= 9 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 11
new energy released= 3.83 TTNT
total energy released= 169,602.46 TTNT

a/s map – 7-8 weeks (1176-1335hrs)

summary

mag1= 1 , mag2= 9 , mag3= 1
mag4= 0 , mag5= 0 , mag6= 0
total= 11
new energy released= 6.40 TTNT
total energy released= 169,605.03 TTNT

a/s map – 8-9 weeks (1335-1512hrs)

summary

mag1= 0 , mag2= 8 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 10
new energy released= 2.20 TTNT
total energy released= 169,670.41 TTNT

aftershock maps 30 day period

a/s map – 9-13 weeks (1512-2260hrs)

summary

mag1= 1 , mag2= 6 , mag3= 6
mag4= 0 , mag5= 0 , mag6= 0
total= 13
new energy released= 11.82 TTNT
total energy released= 169,610.45 TTNT

a/s map – 13-17.3 weeks (2260-2956)

summary

mag1= 2 , mag2= 32 , mag3= 2
mag4= 0 , mag5= 0 , mag6= 0
total= 36
new energy released= 12.12 TTNT
total energy released= 169,610.75 TTNT

a/s map – 17.3-21.7 weeks (2956-3724 hrs)

summary

mag1= 2 , mag2= 28 , mag3= 4
mag4= 0 , mag5= 0 , mag6= 0
total= 34
new energy released= 6.35 TTNT
total energy released= 169,604.98 TTNT

a/s map – 21.7-26 weeks (3724-4300hrs)

summary

mag1= 2 , mag2= 16 , mag3= 6
mag4= 0 , mag5= 0 , mag6= 0
total= 24
new energy released= 17.93 TTNT
total energy released= 169,616.56 TTNT

aftershock map, all events 20/12/2007-20/06/2008 (0-4300hrs) (6 months)

summary

mag1= 38 , mag2= 442 , mag3= 91
mag4= 3 , mag5= 0 , mag6= 1
total= 575
total energy released= 169,598.42 TTNT
.

24 week (6 months) timeline graph

Gisborne 6.7ML 2007 24 weeks aftershock Timeline Graphclick on image for full size version, opens in new tab/window