Archive for August, 2013

August 9, 2013

Cook Strait 18/07-21/08/ 2013, m5.7, 5.8, 6.5, 6.6 and aftershocks

A series of moderate to very strong earthquakes occurred on 18/07/ and 21/07/2013 in Cook Strait, between the North and South Islands of New Zealand. The series eventually included a further very strong event on the 16the August, setting off another series of aftershocks in the area.
The series started with a 5.7ML quake in the morning of Friday the 19th July NZST, which was widely felt in Wellington on the lower North Island.

18/07/2013 Mag 5.7ML

Public ID: 2013p537512
Universal Time: July 18 2013 at 21:06:39
NZ Standard Time: Friday, July 19 2013 at 9:06:39 am
Latitude, Longitude: -41.55, 174.41
Intensity: severe
Focal Depth: 17 km
Magnitude: 5.7216ML
Location: 30 km east of Seddon
Felt Reports: 8269
Energy Released: 5,765.119 Tonnes of TNT (TTNT)

Early analysis of the quake shows the fault moved as a ‘reverse fault’. Where the crust is being compressed, reverse faulting occurs, in which the hanging-wall block moves up and over the footwall block – reverse slip on a gently inclined plane is referred to as thrust faulting.
reverse faulting model
The first aftershock, a 2.53 occured at 18/07/2013 21:11:06 and a further 58 aftershocks over the next 46 hours releasing the equivalent energy of 160.426 (TTNT)

iris snzo webicorder graph 5.7

iris snzo webicorder graph day 199
click image for full size version, opens in new tab/window

5.7 aftershocks map – (46hrs)

5.7 aftershocks graph – (0-46hrs)

5.7 aftershocks graph - 46hrs

summary

mag1= 27 , mag2= 22 , mag3= 8
mag4= 2 , mag5= 1 , mag6= 0
total= 60
total energy released= 5925.54 TTNT

21/07/2013 Mag 5.8ML (5.7Mw)

Public ID: 2013p542711
Universal Time: July 20 2013 at 19:17:10
NZ Standard Time: Sunday, July 21 2013 at 7:17:10 am
Latitude, Longitude: -41.56, 174.40
Intensity: severe
Focal Depth: 20 km
Magnitude: 5.8023ML
Location: 30 km east of Seddon
Felt Reports: 6374
Energy Released: 7,618.304 TTNT

iris snzo webicorder graph 5.8

iris snzo webicorder graph day 201
Like the first 5.7 quake, the 5.8 was a reverse slip/thrust fault type.
The first aftershock of the 5.8, a 4.32ML, occurred at 20/07/2013 19:17:11, with a further 192 aftershocks in the next 9 hours and fifty minutes releasing the equivalent energy of 900.539 TTNT
At this point 14,444.39 TTNT had been released in the series.

GCMT MTS

gcmt moment tensor solution

5.8 aftershocks map – (46-56hrs)

summary

mag1= 21 , mag2= 128 , mag3= 35
mag4= 9 , mag5= 1 , mag6= 0
total= 194
total energy released= 8518.8441 TTNT

5.7 and 5.8 cumulative map – (56hrs)

summary

mag1= 48 , mag2= 150 , mag3= 43
mag4= 11 , mag5= 2 , mag6= 0
total= 254
total energy released= 14,444.390 TTNT

5.7 and 5.8 cumulative graph – (0-56hrs)

5.8 aftershocks graph - 56hrs

21/07/2013 Mag 6.4888ML (6.5Mw)

Public ID: 2013p543824
Universal Time: July 21 2013 at 5:09:30
NZ Standard Time: Sunday, July 21 2013 at 5:09:30 pm
Latitude, Longitude: -41.60, 174.33
Intensity: severe
Focal Depth: 13 km
Magnitude: 6.4888ML
Location: 25 km east of Seddon
Felt Reports: 4384
Energy Released: 81,584.62547 TTNT

The first aftershock of the 6.5, a 4.69 occurred at 21/07/2013 05:13:13 and the next, a 5.2298ML at 21/07/2013 05:13:50. A further moderate aftershock, at 4.997ML occured at 21/07/2013 22:47:25.
As of 26/07/2013 07:18:50UTC there have been 1458 aftershocks of the 6.5, releasing the equivalent energy of 7005.82 TTNT and a total of 1714 since the original 5.7. The total energy released to date 103,034.83 TTNT.
Although severe shaking was experienced on both islands, no one was killed and only a few people were slightly injured from falling objects.
In Wellington the damage was mostly fallen stock in shops and varying degrees of damage to thirty-five buildings within the Wellington CBD with glass from broken windows and plaster falling onto some streets. Monday 22nd the CBD was locked down with workers told to stay home for the day. Several buildings were abandoned until further engineering inspections can be carried out.
White Bluffs near Cape Campbell experienced a major landslide

iris snzo webicorder graph 6.5

note different scale
iris snzo webicorder graph day 202

GCMT MTS

gcmt moment tensor solution

0-120hrs cumulative graph

aftershocks graph - 120hrs
.
.
Unlike the 5.7 and 5.8 thrust earthquakes, the 6.5 quake was a strike-slip event
strikeslip faulting model

6.5 aftershocks map – (0-1hr)

summary

mag1= 0 , mag2= 3 , mag3= 32
mag4= 11 , mag5= 1 , mag6= 1
total= 48
total energy released= 84571.2447 TTNT

6.5 aftershocks map – (1-2hrs)

summary

mag1= 0 , mag2= 17 , mag3= 25
mag4= 5 , mag5= 0 , mag6= 0
total= 47
total energy released= 542.4211 TTNT

6.5 aftershocks map – (2-10hrs)

summary

mag1= 2 , mag2= 98 , mag3= 78
mag4= 9 , mag5= 0 , mag6= 0
total= 187
total energy released= 1097.030 TTNT

6.5 a/s map – (0-10hrs cumulative)

summary

mag1= 1, mag2= 118, mag3= 135
mag4= 25, mag5= 1, mag6= 1
total= 282
total energy released= 86,210.70 TTNT

6.5 aftershocks map – (10-18hrs)

summary

mag1= 9 , mag2= 106 , mag3= 48
mag4= 3 , mag5= 1 , mag6= 0
total= 167
total energy released= 1277.389 TTNT

6.5 a/s map – (0-18hrs cumulative)

summary

mag1= 11, mag2= 224, mag3= 183
mag4= 28, mag5= 2, mag6= 1
total= 449
total energy released= 87488.084 TTNT

6.5 aftershocks map – (18-24hrs)

summary

mag1= 7 , mag2= 77 , mag3= 19
mag4= 2 , mag5= 0 , mag6= 0
total= 105
total energy released= 293.775 TTNT

6.5 a/s map – (0-24hrs cumulative)

summary

mag1= 18, mag2= 301, mag3= 202
mag4= 30, mag5= 2, mag6= 1
total= 554
total energy released= 87781.86 TTNT

m6.5, end of 6-8 hourly maps ~ start of 12 hourly maps

6.5 aftershocks map – (24-36hrs)

summary

mag1= 30 , mag2= 139 , mag3= 32
mag4= 6 , mag5= 0 , mag6= 0
total= 207
total energy released= 780.463 TTNT

6.5 a/s map – (0-36hrs cumulative)

summary

mag1= 48, mag2= 440, mag3= 234
mag4= 36, mag5= 2, mag6= 1
total= 761
total energy released= 88,562.322 TTNT

6.5 aftershocks map – (36-48hrs)

summary

mag1= 29 , mag2= 124 , mag3= 19
mag4= 2 , mag5= 0 , mag6= 0
total= 174
total energy released= 248.480 TTNT

6.5 a/s map – (0-2days cumulative)

summary

mag1= 77, mag2= 564, mag3= 253
mag4= 38, mag5= 2, mag6= 1
total= 935
total energy released= 88,810.802 TTNT

6.5 aftershocks map – (48-60hrs)

summary

mag1= 21 , mag2= 102 , mag3= 13
mag4= 1 , mag5= 0 , mag6= 0
total= 137
total energy released= 56.112 TTNT

6.5 a/s map – (0-60hrs cumulative)

summary

mag1= 98, mag2= 666, mag3= 266
mag4= 39, mag5= 2, mag6= 1
total= 1072
total energy released= 88866.915 TTNT

6.5 aftershocks map – (60-72hrs)

summary

mag1= 22 , mag2= 66 , mag3= 11
mag4= 4 , mag5= 0 , mag6= 0
total= 103
total energy released= 240.542 TTNT

6.5 a/s map – (0-3days cumulative)

summary

mag1= 120, mag2= 732, mag3= 277
mag4= 43, mag5= 2, mag6= 1
total= 1176
total energy released= 89,107.457 TTNT

72 hour timeline graph

m6.5 Cook Strait 72hr timeline graph
click on image for larger version

m6.5, end of 12 hourly maps ~ start of 24 hourly maps

6.5 aftershocks map – (3-4days)

summary

mag1= 34 , mag2= 124 , mag3= 26
mag4= 4 , mag5= 0 , mag6= 0
total= 188
total energy released= 275.505 TTNT

6.5 a/s map – (0-4 days cumulative)

summary

mag1= 154, mag2= 856, mag3= 303
mag4= 47, mag5= 2, mag6= 1
total= 1,364
total energy released= 89,382.962 TTNT

6.5 aftershocks map – (4-5days)

summary

mag1= 33 , mag2= 91 , mag3= 7
mag4= 1 , mag5= 0 , mag6= 0
total= 132
total energy released= 64.220 TTNT

6.5 a/s map – (0-5 days cumulative)

summary

mag1= 187, mag2= 947, mag3= 310
mag4= 48, mag5= 2, mag6= 1
total= 1,496
total energy released= 89,447.182 TTNT

6.5 aftershocks map – (5-6days)

summary

mag1= 25 , mag2= 109 , mag3= 13
mag4= 0 , mag5= 0 , mag6= 0
total= 147
total energy released= 32.589 TTNT

6.5 a/s map – (0-6 days cumulative)

summary

mag1= 212, mag2= 1,056, mag3= 323
mag4= 48, mag5= 2, mag6= 1
total= 1,643
total energy released= 89,479.771 TTNT

6.5 aftershocks map – (6-7days)

summary

mag1= 36 , mag2= 87 , mag3= 9
mag4= 1 , mag5= 0 , mag6= 0
total= 133
total energy released= 117.516 TTNT

6.5 a/s map – (0-4 days cumulative)

summary

mag1= 248, mag2= 1,143, mag3= 332
mag4= 49, mag5= 2, mag6= 1
total= 1,776
total energy released= 89,597.287 TTNT

6.5 aftershocks map – (7-8days)

summary

mag1= 57 , mag2= 86 , mag3= 12
mag4= 0 , mag5= 1 , mag6= 0
total= 156
total energy released= 1,849.018 TTNT

6.5 a/s map – (0-8 days cumulative)

summary

mag1= 305, mag2= 1,229, mag3= 344
mag4= 49, mag5= 3, mag6= 1
total= 1,932
total energy released= 91,446.305 TTNT

28/07/2013 Mag 5.3876ML (4.9Mw)

Public ID: 2013p563639
Universal Time : July 28 2013 at 13:07:14
NZ Standard Time: Monday, July 29 2013 at 1:07:14 am
Latitude, Longitude: -41.69, 174.30
Intensity : severe
Focal Depth: 11.7 km
Magnitude: 5.3876ML
Location: 20 km east of Seddon
Felt Reports: 2422
Energy Released: 1,818.898 TTNT
This event occurred 7 days, 7 hours, 57 minutes after the 6.5 event and 9 days, 16 hours after the first 5.7 event on 18-07-2013 and was located further south than the previous larger earthquakes, 3km NNE off Cape Campbell.

iris snzo webicorder graph 5.4

iris snzo webicorder graph day 209

6.5 aftershocks map – (8-9days)

summary

mag1= 73 , mag2= 37 , mag3= 7
mag4= 1 , mag5= 0 , mag6= 0
total= 118
total energy released= 48.141 TTNT

6.5 a/s map – (0-9 days cumulative)

summary

mag1= 378, mag2= 1,266, mag3= 351
mag4= 50, mag5= 3, mag6= 1
total= 2,050
total energy released= 91,494.446 TTNT

6.5 aftershocks map – (9-10days)

summary

mag1= 49 , mag2= 42 , mag3= 3
mag4= 0 , mag5= 0 , mag6= 0
total= 94
total energy released= 6.117 TTNT

6.5 a/s map – (0-10 days cumulative)

summary

mag1= 427, mag2= 1,308, mag3= 354
mag4= 50, mag5= 3, mag6= 1
total= 2,144
total energy released= 91,500.563 TTNT

6.5 aftershocks map – (10-11days)

summary

mag1= 51 , mag2= 41 , mag3= 10
mag4= 3 , mag5= 0 , mag6= 0
total= 105
total energy released= 415.385 TTNT

6.5 a/s map – (0-11 days cumulative)

summary

mag1= 478, mag2= 1,349, mag3= 364
mag4= 53, mag5= 3, mag6= 1
total= 2,249
total energy released= 91,915.948 TTNT

6.5 aftershocks map – (11-12days)

summary

mag1= 16 , mag2= 79 , mag3= 6
mag4= 1 , mag5= 1 , mag6= 0
total= 103
total energy released= 1062.267 TTNT

6.5 a/s map – (0-12 days cumulative)

summary

mag1= 495, mag2= 1,412, mag3= 340
mag4= 49, mag5= 3, mag6= 1
total= 2,300
total energy released= 92,033.312 TTNT

28/07/2013 Mag 5.203ML (4.9mb)

Public Id: 2013p574429
Universal Time: 2013/08/01 at 12:56:12
Local time (NZST): Friday 02 August 2013 at 12:56 AM
Latitude, Longitude: 41.78S, 174.31E
Location: 25 km south-east of Seddon
Depth: 6 km
Magnitude: 5.203ML
Felt Reports: 479
Energy Released: 964.069 TTNT
located 4km east of Cape Campbell

iris snzo webicorder graph 5.2

iris snzo webicorder graph day 209

6.5 aftershocks map – (12-13days)

summary

mag1= 20 , mag2= 66 , mag3= 7
mag4= 1 , mag5= 0 , mag6= 0
total= 94
total energy released= 46.128 TTNT

6.5 a/s map – (0-13 days cumulative)

summary

mag1= 515, mag2= 1,478, mag3= 347
mag4= 50, mag5= 3, mag6= 1
total= 2,394
total energy released= 92,079.44 TTNT

6.5 aftershocks map – (13-14days)

summary

mag1= 25 , mag2= 42 , mag3= 4
mag4= 1 , mag5= 0 , mag6= 0
total= 72
total energy released= 24.456 TTNT

6.5 a/s map – (0-14 days cumulative)

summary

mag1= 540, mag2= 1,520, mag3= 351
mag4= 51, mag5= 3, mag6= 1
total= 2,466
total energy released= 92,103.896 TTNT

14 day timeline graph

Cook Strait 14 day timeline graph
click on image for larger version
.

16/08/2013 Mag 6.6ML

Public ID: 2013p613797
Universal Time: August 16 2013 at 2:31:05
NZ Standard Time: Friday, August 16 2013 at 2:31:05 pm
Latitude, Longitude: -41.73, 174.15
Intensity: severe
Focal Depth: 8 km
Magnitude: 6.6382 ML (6.5Mw)
Location 10 km south-east of Seddon
Felt Reports: 4989
Energy Released: 136,681.056 Tonnes of TNT (TTNT)
Casualties: Four minor injuries, one serious medical condition reported
Called the “Lake Grassmere earthquake” The focal mechanism shows it to be a strike-slip earthquake, similar to the M6.5 earthquake in July.
The largest land shift was recorded at Cape Campbell, land here moved 18 cm to the west. Beneath the earth’s surface, the maximum movement on the fault is approximately 3m which occurred 8km below Lake Grassmere. The fault movement is spread over an area 10km in length; this extends from 4km to 14km below the earth’s surface.

iris snzo webicorder graph 6.6 and 5.9 etc aftershocks

iris snzo webicorder graph day 199
click image for full size version, opens in new tab/window

GCMT MTS

GCMT MTS 6-5MWCOOKSTRAIT2013-08-16
click image for full size version, opens in new tab/window

The largest land shift was recorded at Cape Campbell, land here moved 18 cm to the west. Beneath the earth’s surface, the maximum movement on the fault is approximately 3m which occurred 8km below Lake Grassmere. The fault movement is spread over an area 10km in length; this extends from 4km to 14km below the earth’s surface.
Five m5+ aftershocks were recorded in the first hour after the main shock and what was to be the largest aftershock, a 5.9759ML (5.8Mw) was recorded 3 hours after at 5:31pm NZST. A further eight m5+ quakes were felt through to the 37 hr mark. All these 5m+ and several high m4 quakes were felt in Wellington and the Kapiti Coast.

.

6.6 aftershocks map – (0-1hr)

summary

mag1= 0 , mag2= 0 , mag3= 2
mag4= 10 , mag5= 5 , mag6= 1
total= 18
total energy released= 145463.615 TTNT

6.6 aftershocks map – (1-2hrs)

summary

mag1= 0 , mag2= 4 , mag3= 21
mag4= 3 , mag5= 1 , mag6= 0
total= 29
total energy released= 3822.671 TTNT

largest aftershock

Public Id: 2013p614135
Universal Time: 2013/08/16 at 05:31:15
Local time (NZST): Friday 16 August 2013 at 05:31 PM
Latitude, Longitude: 41.73S, 174.29E
Location: 20 km east of Seddon
Depth: 10 km
Magnitude: 5.9759ML (5.8Mw)
Intensity: severe
Felt Reports: 1191
Energy Released: 13,875.809 Tonnes of TNT (TTNT)
Located 11.67 km NE of the Lake Grassmere 6.5, in Clifford Bay.

3 hour timeline graph

Cook Strait 6.6 3hr timeline graph
click on image for larger version

GCMT MTS

GCMT MTS 5-8MWCOOKSTRAIT2013-08-16
click image for full size version, opens in new tab/window

6.6 aftershocks map – (2-10hrs)

summary

mag1= 1 , mag2= 87 , mag3= 80
mag4= 13 , mag5= 6 , mag6= 0
total= 187
total energy released= 20,968.251 TTNT

6.6 a/s map – (0-10hrs cumulative)

summary

mag1= 1 , mag2= 91 , mag3= 103
mag4= 26 , mag5= 12 , mag6= 1
total= 234
total energy released= 170,254.537 TTNT

6.6 aftershocks map – (10-18hrs)

summary

mag1= 3 , mag2= 115 , mag3= 39
mag4= 3 , mag5= 0 , mag6= 0
total= 160
total energy released= 567.727 TTNT

6.6 a/s map – (0-18hrs cumulative)

summary

mag1= 4 , mag2= 206 , mag3= 142
mag4= 29 , mag5= 12 , mag6= 1
total= 394
total energy released= 170,822.264 TTNT

6.6 aftershocks map – (18-24hrs)

summary

mag1= 7 , mag2= 60 , mag3= 19
mag4= 5 , mag5= 0 , mag6= 0
total= 91
total energy released= 168.215 TTNT

6.6 a/s map – (0-24hrs cumulative)

summary

mag1= 11 , mag2= 266 , mag3= 161
mag4= 34 , mag5= 12 , mag6= 1
total= 485
total energy released= 170,990.479 TTNT

m6.6, end of 6-8 hourly maps ~ start of 12 hourly maps

6.6 aftershocks map – (24-36hrs)

summary

mag1= 16 , mag2= 126 , mag3= 29
mag4= 6 , mag5= 2 , mag6= 0
total= 179
total energy released= 3589.674 TTNT

6.6 a/s map – (0-36hrs cumulative)

summary

mag1= 27 , mag2= 392 , mag3= 190
mag4= 40 , mag5= 14 , mag6= 1
total= 664
total energy released= 174,580.153 TTNT

6.6 aftershocks map – (36-48hrs)

summary

mag1= 14 , mag2= 112 , mag3= 9
mag4= 2 , mag5= 1 , mag6= 0
total= 138
total energy released= 674.867 TTNT

6.6 a/s map – (0-2days cumulative)

summary

mag1= 41 , mag2= 504 , mag3= 199
mag4= 42 , mag5= 15 , mag6= 1
total= 802
total energy released= 175,255.020 TTNT

6.6 aftershocks map – (48-60hrs)

summary

mag1= 16 , mag2= 88 , mag3= 9
mag4= 0 , mag5= 0 , mag6= 0
total= 113
total energy released= 50.104 TTNT

6.6 a/s map – (0-60hrs cumulative)

summary

mag1= 57 , mag2= 592 , mag3= 208
mag4= 42 , mag5= 15 , mag6= 1
total= 915
total energy released= 175,305.124 TTNT

6.6 aftershocks map – (60-72hrs)

summary

mag1= 18 , mag2= 75 , mag3= 9
mag4= 1 , mag5= 0 , mag6= 0
total= 103
total energy released= 53.274 TTNT

6.6 a/s map – (0-3days cumulative)

summary

mag1= 75 , mag2= 667 , mag3= 217
mag4= 43 , mag5= 15 , mag6= 1
total= 1,018
total energy released= 175,358.398 TTNT

72 hour timeline graph, m6.6

m6.6 Cook Strait 72hr timeline graph
click on image for larger version

timeline graph, 30days

Cook Strait 30day timeline graph
click on image for larger version

… to be continued…………..

acknowledgements:
Fault diagrams: ©Redrawn from University of Otago (Richard Sibson)
Moment Tensor Solutions: Wilber 3/GCMT
Data: Geonet/GNS
Webicorder Graphs: IRIS/ Buffer of Uniform Data /Quality Analysis Control Kit

updated on Aug 23, 2013 at 13:13 NZST

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