It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
Friday, June 17, 2011 at 09:16:12 UTC
Friday, June 17, 2011 at 12:16:12 PM at epicenter
Time of Earthquake in other Time Zones
10 km (6.2 miles)
ERITREA - ETHIOPIA REGION
120 km (74 miles) WNW of Assab, Eritrea
215 km (133 miles) SW of Al Hudaydah, Yemen
238 km (147 miles) E of Mekele, Ethiopia
371 km (230 miles) SE of ASMARA, Eritrea
horizontal +/- 17.3 km (10.7 miles); depth +/- 2.7 km (1.7 miles)
NST=161, Nph=165, Dmin=326.2 km, Rmss=1.13 sec, Gp= 65°,
M-type=regional moment magnitude (Mw), Version=6
USGS NEIC (WDCS-D)
Weber 1, 2 ,3, 4 Swarm
A series of four large earthquakes with epicenters very close to one another occurred in 1990–1992 in the Weber region of the southeast coast of the North Island. The region is one of oblique plate convergence and subduction, the plate interface being at about 20 km depth.
The first event in the Weber sequence was the M6.2 Weber I in Feb. 1990, which faulted the plate slab steeply down to the northwest. That was followed 3 months later by the M6.4 Weber II event, which was a southeast-directed thrust entirely above the plate interface.
The first event, on February 19, 1990 at 05:34:37 UTC, a 5.944ML, 6.2Mw, at a depth of 33.8km, occurred within the upper part of the subducting Pacific plate on a steeply northwest dipping normal fault, as defined by relocated aftershocks. .The time history of the aftershocks of the first (deeper) event shows a period of quiescence beginning 35 days before the second (shallow) event in May.
Between the main shock on the 19th February and the 2nd event on the 13th May in the approx. 50km radius triangular area between Dannevirke in the north west, Pourerere in the north east and Owahanga in the south there were 1354 aftershocks, 7 between 4.016ML and 4.899ML , 111 between 3.001ML and 3.989ML, 872 between 2.002ML and 2.992ML and 363 between 1.209ML and 1.999ML. The majority of the smaller aftershocks were 4-16km northwest of Weber or 15-22km north west of the main shock., although there were approx. 23 events further to the west 14-15km east of Ekatahuna running in a north south line north of Alfredton, including a 4.553ML.
The second event, May 13, 1990, 6.2ML, 6.5Ms, 6.4 Mw, occurred on an imbricate fault in the overlying Australian plate, dipping shallowly northwest, with components of both thrusting and dextral strike-slip motion. It was located 5.41km (3.4 miles) north east of the February Weber 1 event at a depth of 30km.
There were 441 aftershocks in the first 24 hours, the largest being a 5.055ML 17.6km to the north west, at a depth of 26.4km, subsequent to and 3 minutes after the mainshock, and 29 events between 4.003ML and 4.791ML by August 1st, 22 of them in the first 16 hours.
Through till 15th August 1990 there were 235 aftershocks between 3.0ML and 3.969ML, 718 events 2.003ML to 2.994ML and 563 events 0.357ML to 1.995ML. In total there were 1546 aftershocks before the Weber 3 5.7ML struck on 15th August 1990.
It appears that the first earthquake (Weber 1) , in the lower plate, produced additional loading that induced the second. This interactive relationship is also evident in the aftershocks of the May event, many of which were located near to the Feb 19 hypocentre.
News Item 13 May 1990 Weber 2 earthquake:
At 4:23 pm on Mother’s Day, 13 May 1990, a magnitude 6.5 earthquake struck the southern Hawke’s Bay near Weber, east of Dannevirke. It was just 10 kilometres from the epicentre of a magnitude 6.1 Mwearthquake on 19 February, a few months earlier. Some houses were cracked, or knocked off their foundations. Many buildings in Dannevirke had broken windows and cracked chimneys. At Cape Kidnappers, a group of about ten people walking along the shore had a near miss when a large slip from the coastal cliffs fell near them. Within 24 hours of the main earthquake, there were 7 aftershocks of magnitude 5 Mw or greater.
The third smaller Weber 3 earthquake occured on August 15, 1990 at 15:54:43.4 UTC, was a 5.7ML, 4.8Ms, 5.17Mw at a depth of 41.7km and extended the aftershock zone of the deeper first main shock to the northeast, matching the extent of the shallower second 6.2ML Weber 2 shock. In the 122 days following, to the end of 1990, there were 4 aftershocks 4.062ML to 4.777ML, 45 events 3.001ML to 3.937ML, 285 events 2.012ML to 2.995ML and 21 events 1.662ML to 1.981ML
From the beginning of Jan 1991 in the 14 months through to 1st March 1992 the area was relatively light with earthquake activity, with only 351 total events, 4 from 4.205ML to 4.381ML, 65 from 3.015ML to 3.92ML, 278 from 2.044ML to 2.999ML and 3 at 1.921ML, 1.969ML and 1.977ML
1992 Weber 4:
"Weber 4" 5.7ML occured on 1992-03-02 09:05:57 UTC, the 4th event in a sequence starting on February 19, 1990, with a 5.9ML ( Mw 6.2). The second event, May 13, 1990 a 6.2ML(6.4Mw), and the 3rd event August 15, 1990 a 5.7ML.
The Weber 4 earthquake epicentre was closer to the coast than the previous 3 quakes, it was 7.2km east of Weber 3 at a depth of 37km.
There were 406 aftershocks in the 30 days following, the largest a 5.016ML event on the 13th March at Lat -40.26044 Long. 176.49117, 21.07km to the north west of the main shock. There were 138 aftershocks from 1.004ML to 2.819 in the immediate area of the mainshock, the remaining 268 aftershocks spread in two main areas in a SW to NE direction, one near the 1990 Weber 3 earthquake and the others 20 km north east of Weber village. Of those there were 2 aftershocks 4.216ML and 4.392ML, 17 between 3.004ML and 3.976ML 186 events 2.005ML to 2.993ML and 62 events 0.453ML to 1.989ML
Originally posted by Anneke
Hi, I'm a newbie but have been following this thread for a while now. Moving to New Zealand, played a part in that I guess.
I'm not a scientist or geologist or anything near, I'm just very curious and like everybody in NZ I've been following the events in Christchurch and the rumours surrounding them especially the talk about the "extinct" volcanoes there. It reminds me of Montserrat and what happened there in the ninetees. They had three years of hightened seismic activity and then their "extinct" volcano erupted.
Originally posted by Evltre
reply to post by muzzy
I'm really concerned too. I think we're possibly just beginning here! They keep moving east - heading for the chatham rise and there are some BIG faults out there! Is it possible that we're just starting the giggle of the west end of those faults?