Dusky Sound 7.8Mw, 15/07/2009 and aftershocks

15/07/2009 Mag 7.8Mw

Public ID:3124785
Lat/Long: -45.7702, 166.5871
Date/Time UTC: 15/07/2009 09:22:29
Depth: 12 km
No. of Phases used: 19
Status: reviewed
Location: N of Indian Island, Dusky Sound, Fiordland (geonet)
Energy Released: 7,558,025.0004 tonnes of TNT
Casualties: None
.
The Mw 7.6 Dusky Sound earthquake of July 15th, 2009, was the largest magnitude earthquake in New Zealand since the devastating 1931 Hawke’s Bay event (Ms 7.8). The earthquake was sufficiently large to generate at least a 2.3 m wave at Passage Point. Despite its large magnitude, this event resulted in relatively minimal damage when compared to worldwide events of a similar size. This can be explained as a fortunate combination of the sparse population of the area and the specific physical characteristics of the earthquake. Centroid Moment Tensor (CMT) solutions define the rupture surface as a low-angle plane and finite fault inversions confirm the slip occurred on the interface between the eastward-subducting Australian plate and overriding Pacific plate, initiating at about 30 km depth and rupturing upward and southwestward to about 15 km depth. The oceanward rupture directivity likely contributed to the lower intensity of measured ground motion than might be expected for such a large, shallow event. The amount of radiated seismic energy from the earthquake was relatively small.
Seismic recordings show relatively little high-frequency content. The earthquake also triggered few landslides, about half of the amount triggered by the 2003 Mw 7.2 Fiordland earthquake. Analysis of the focal mechanism suggests that the southwestward directivity of the rupture focused much of the radiated energy offshore.

GCMT MTS

GCMT MTS DUSKY SOUND NZ 7-8MW 15-07-2009

This Fiordland earthquake caused power outages in several parts of the South Island and only minor damage. Reported damage includes a broken water main at Winton, cracks in exterior walls of buildings at Invercargill and items falling from shelves throughout the Southland region. Measurements indicate a geographic shift to the west towards Australia of 30.5 cm of the southern tip of the South Island.
Over the past two decades, several large earthquakes have occurred in Fiordland, predominantly in a cluster to the northeast of today’s earthquake. Though the faulting mechanisms of those events are similar to the 15th July earthquake, their slip vectors are rotated clockwise with respect to plate motions, and thus may not represent exactly the same style of faulting.
The most recent of these previous large events occurred on August 21st 2003 when a magnitude 7.2 Mw earthquake approximately 100 km to the northwest caused minor damage in Otago and Southland, and numerous landslides across the Fiordland region. A magnitude 6.7 event on August 10, 1993 caused power outages in the Te Anau area and was felt throughout South Island and as far away as Sydney, Australia. A magnitude 6.1 earthquake struck on May 31, 1989 and was felt strongly in the southwestern part of South Island and a magnitude 6.7 quake struck on 3rd June 1988 near Charles Sound.

Tsunami

A tsunami resulting from the earthquake was observed and recorded in several ways: by the observations of the occupants of boats present in thesounds near the epicentre, by an Australian deep-ocean buoy in the Tasman Sea, and on tide gauges throughout the Pacific. In addition a post-eventsurvey uncovered evidence of the environmental impact of the tsunami on specific locations within the sounds. At Jackson Bay the maximum amplitude
was 500 mm (peak-to-trough 1m). Interestingly, the largest wave here was almost two hours after the initial arrival, a similar delay in the maximum wave was observed in 2003 following an Mw7.2 Fiordland earthquake located just to the north of the most recent event.

7.8Mw location (geonet)

Networks estimates of location

aftershock maps

Data from the Geonet database are limited to the polygon area -45.3S,164.5E,-45.3S,168.15E,-48.0S,168.15E,-48.0S,164.5E. Some events may fall outside the borders of the map, especially to the SSW 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

7.8 aftershocks map – (0-1hr)

summary

mag1= 0 , mag2= 0 , mag3= 0

mag4= 27 , mag5= 18 , mag6= 1, mag7= 1

total= 46
total energy released= 7,606,275.20 TTNT

7.8 aftershocks map – (1-4hrs)

summary

mag1= 0 , mag2= 0 , mag3= 56

mag4= 61 , mag5= 5 , mag6= 0

total= 122
new energy released= 9,273.66 TTNT
total energy released= 7,615,548.85 TTNT

7.8 aftershocks map – (4-8hr)

summary

mag1= 0 , mag2= 3 , mag3= 84
mag4= 32 , mag5= 2 , mag6= 0

total= 121
new energy released= 7,709.19 TTNT
total energy released= 7,623,258.04 TTNT

7.8 aftershocks map – (8-12hrs)

summary

mag1= 0 , mag2= 0 , mag3= 1
mag4= 5 , mag5= 0 , mag6= 0

total= 6
new energy released= 745.00 TTNT
total energy released= 7,624,003.04 TTNT

7.8 aftershocks map – (12-16hr)

summary

mag1= 0 , mag2= 0 , mag3= 7
mag4= 8 , mag5= 5 , mag6= 0

total= 20
new energy released= 7,994.40 TTNT
total energy released= 7,631,997.44 TTNT

7.8 aftershocks map – (16-20hrs)

summary

mag1= 0 , mag2= 0 , mag3= 1
mag4= 2 , mag5= 1 , mag6= 0

total= 4
new energy released= 1,487.50 TTNT
total energy released= 7,633,484.94 TTNT

7.8 aftershocks map – (20-24hr)

summary

mag1= 0 , mag2= 1 , mag3= 10
mag4= 6 , mag5= 2 , mag6= 0

total= 19
new energy released= 6,509.46 TTNT
total energy released= 7,639,994.39 TTNT

7.8 a/s map – (24hrs cumulative)

summary

mag1= 0 , mag2= 4 , mag3= 159
mag4= 141 , mag5= 33 , mag6= 1, mag7= 1
total= 339
total energy released= 7,639,994.39 TTNT

aftershock maps 12 hour period

7.8 aftershocks map – (24-36hrs)

summary

mag1= 0 , mag2= 1 , mag3= 3
mag4= 6 , mag5= 2 , mag6= 0
total= 12
new energy released= 4,653.34 TTNT
total energy released= 7,644,647.73 TTNT

7.8 aftershocks map – (36-48hrs)

summary

mag1= 1 , mag2= 70 , mag3= 109
mag4= 22 , mag5= 3 , mag6= 0
total= 205
new energy released= 11,999.85 TTNT
total energy released= 7,656,647.58 TTNT

7.8 aftershocks map – (48-60hrs)

summary

mag1= 0 , mag2= 3 , mag3= 84
mag4= 32 , mag5= 2 , mag6= 0
total= 121
new energy released= 7,709.19 TTNT
total energy released= 7,623,258.04 TTNT

7.8 aftershocks map – (60-72hrs)

summary

mag1= 0 , mag2= 0 , mag3= 1
mag4= 5 , mag5= 0 , mag6= 0
total= 6
new energy released= 745.00 TTNT
total energy released= 7,624,003.04 TTNT

72hr timeline graph

Dusky Sound 7.8Mw aftershock Timeline Graphclick on image for full size version, opens in new tab/window

aftershock maps 24 hour period

7.8 a/s map – 3-4 days (72-96hr)

summary

mag1= 0 , mag2= 54 , mag3= 64
mag4= 12 , mag5= 3 , mag6= 0
total= 133
new energy released= 4,044.84 TTNT
total energy released= 7,662,246.25 TTNT

7.8 a/s map – 4-5 days (96-120hrs)

summary

mag1= 2 , mag2= 77 , mag3= 48
mag4= 6 , mag5= 0 , mag6= 0
total= 133
new energy released= 321.46 TTNT
total energy released= 7,662,567.71 TTNT

7.8 a/s map – 5-6 days(120-144hrs)

summary

mag1= 0 , mag2= 52 , mag3= 39
mag4= 2 , mag5= 0 , mag6= 0
total= 93
new energy released= 200.00 TTNT
total energy released= 7,662,767.71 TTNT

7.8 a/s map – 6-7days (144-168hrs)

summary

mag1= 0 , mag2= 15 , mag3= 24
mag4= 11 , mag5= 0 , mag6= 0
total= 50
new energy released= 792.82 TTNT
total energy released= 7,663,560.53 TTNT

7 day (168hrs) timeline graph

Dusky Sound 7.8Mw aftershock 7 day Timeline Graphclick on image for full size version, opens in new tab/window
.

7.8 a/s map – 7-8 days (168-192hrs)

summary

mag1= 0 , mag2= 14 , mag3= 18
mag4= 1 , mag5= 0 , mag6= 0
total= 33
new energy released= 75.42 TTNT
total energy released= 7,663,635.95 TTNT

7.8 a/s map – 8-9days (192-216hrs)

summary

mag1= 0 , mag2= 11 , mag3= 19
mag4= 3 , mag5= 0 , mag6= 0
total= 33
new energy released= 195.30 TTNT
total energy released= 7,663,831.26 TTNT

7.8 a/s map – 9-10 days (216-240hrs)

summary

mag1= 0 , mag2= 21 , mag3= 16
mag4= 1 , mag5= 0 , mag6= 0
total= 38
new energy released= 203.92 TTNT
total energy released= 7,664,035.18 TTNT

7.8 a/s map – 10-11 days (240-264hrs)

summary

mag1= 0 , mag2= 14 , mag3= 13
mag4= 1 , mag5= 0 , mag6= 0
total= 28
new energy released= 129.34 TTNT
total energy released= 7,664,164.06 TTNT

7.8 a/s map – 11-12 days (264-288hrs)

summary

mag1= 0 , mag2= 34 , mag3= 8
mag4= 1 , mag5= 0 , mag6= 0
total= 43
new energy released= 260.39 TTNT
total energy released= 7,664,424.45 TTNT

7.8 a/s map – 12-13 days (288-312hrs)

summary

mag1= 0 , mag2= 9 , mag3= 16
mag4= 1 , mag5= 0 , mag6= 0
total= 26
new energy released= 179.93 TTNT
total energy released= 7,664,604.37 TTNT

7.8 a/s map – 13-14 days (312-336hrs)

summary

mag1= 0 , mag2= 10 , mag3= 13
mag4= 1 , mag5= 0 , mag6= 0
total= 24
new energy released= 98.56 TTNT
total energy released= 7,664,702.94 TTNT

7.8 a/s map – 0-14days (0-336hrs)

summary

mag1= 3 , mag2= 443 , mag3= 644
mag4= 221 , mag5= 41 , mag6= 1
total= 1,353
total energy released= 7,664,702.94 TTNT

14 day (336hrs) timeline graph

Dusky Sound 7.8Mw aftershock 14 day Timeline Graphclick on image for full size version, opens in new tab/window

aftershock maps 7 day period

a/s map – 2-3 weeks (336-504hrs)

summary

mag1= 0 , mag2= 65 , mag3= 70
mag4= 17 , mag5= 5 , mag6= 0
total= 157
new energy released= 14,694.51 TTNT
total energy released= 7,679,397.45 TTNT

a/s map – 3-4 weeks (504-672hrs)

summary

mag1= 0 , mag2= 62 , mag3= 45
mag4= 10 , mag5= 0 , mag6= 0
total= 117
new energy released= 1,320.78 TTNT
total energy released= 7,666,023.72 TTNT

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