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Earthquake M6.5 - 29km SSE of Blenheim, New Zealand 2013-08-16 02:31:07 UTC (USGS, extract)

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  • Earthquake M6.5 - 29km SSE of Blenheim, New Zealand 2013-08-16 02:31:07 UTC (USGS, extract)

    [Source: USGS, full page: (LINK). Extract.]

    Earthquake M6.5 - 29km SSE of Blenheim, New Zealand 2013-08-16 02:31:07 UTC


    Location and Magnitude contributed by: USGS, NEIC, Golden, Colorado (and predecessors)

    • New Zealand / Coordinates: 41.767?S, 174.061?E / Depth: 10.0km (6.2mi)

    Event Time
    • 2013-08-16 02:31:07 UTC
    • 2013-08-16 14:31:07 UTC+12:00 <ABBR>at epicenter</ABBR>
    • <ABBR></ABBR>2013-08-16 04:31:07 UTC+02:00 <ABBR>system time</ABBR>

    41.767?S 174.061?E depth=10.0km (6.2mi)

    Nearby Cities
    • 29km (18mi) SSE of Blenheim, New Zealand
    • 77km (48mi) SW of Karori, New Zealand
    • 80km (50mi) SW of Wellington, New Zealand
    • 84km (52mi) SE of Nelson, New Zealand
    • 87km (54mi) ESE of Richmond, New Zealand
    Related Links
    Tectonic Summary

    The M 6.5 August 16, 2013 earthquake south of Blenheim, New Zealand, occurred as the result of strike-slip faulting on or near the plate boundary between the Pacific and Australia plates. At the latitude of this event, the Pacific plate moves towards the WSW with respect to Australia at a rate of approximately 41 mm/yr. Preliminary faulting mechanisms for the earthquake suggest it is related to either NE-SW right-lateral strike-slip motion (consistent with plate boundary oriented deformation), or NW-SE left-lateral strike-slip motion.

    This region of New Zealand has hosted a number of small-moderate sized earthquakes in recent weeks, including a M 6.5 earthquake approximately 40 km east of the August 16 event in the Cook Straight, on July 21, 2013.

    The July 21 event was preceded by several M 5.3-5.8 events and was followed by a dozen or more aftershocks between M 4.5-5.0, delineating shallow upper plate structures aligned NE-SW, and some deeper subduction-related activity, mostly offshore of the north coast of New Zealand?s South Island.

    In contrast to the earlier events, the August 16 earthquake is on land, near the eastern end of the complex Marlborough Fault System. The event is located approximately 10 km southeast of the Awatere Fault in the vicinity of Lake Grassmere. The Marlborough Fault system is characterized by a series of NE striking right-lateral strike slip faults that have dismembered the northern South Island into a series of crustal blocks that are being transported to the northeast. Although there is no specific mapped surface fault that can be linked to the August 16 event at this time, the NE trending fault plane is similarly oriented to the Awatere and Clarence faults of the Marlborough system. In 1966 a M 5.8 earthquake (interpreted to have occurred offshore to the NE of the August 16 event) was widely felt in this area, causing surface deformation of the main railroad line in the region. That event is interpreted to have occurred on a blind structure sub-parallel to the Awatere fault to its northeast.



  • #2
    Re: Earthquake M6.5 - 29km SSE of Blenheim, New Zealand 2013-08-16 02:31:07 UTC (USGS, extract)

    Earthquakes shake central New Zealand

    Strong earthquakes shook central New Zealand on Friday, damaging homes, destroying a bridge and sending office workers scrambling for cover in the capital. No serious injuries have been reported.

    A magnitude-6.5 temblor struck just after 2:30 p.m. local time near the small South Island town of Seddon, and at least six aftershocks were 5.0 magnitude or stronger.

    Several homes near the epicenter were severely damaged, with chimneys collapsing and roofs caving in, said police spokeswoman Barbara Dunn. She said a bridge was severely damaged on the main highway near Seddon, and that rocks and debris had fallen onto the road. Police closed a section of the highway.

    Some buildings in Wellington, the capital, were evacuated, and items were knocked off shelves in places.



    • #3
      Re: Earthquake M6.5 - 29km SSE of Blenheim, New Zealand 2013-08-16 02:31:07 UTC (USGS, extract)

      Damaging quake hits the north-east of the South Island

      Skip to end of metadataGo to start of metadata

      <ARTICLE>Another severe, damaging quake struck in the afternoon of Friday 16 August. Damage has been reported both sides of the Cook Strait.

      <TABLE><TBODY><TR><TD style="WIDTH: 300px" class=gallery-image></TD></TR><TR><TD style="WIDTH: 300px">Today's quake has a strike-slip mechanism.

      </TD></TR><TR><TD style="WIDTH: 300px" class=gallery-image></TD></TR><TR><TD style="WIDTH: 300px">The "ShakeMap" showing the shaking intensity as determined by GeoNet instruments and modelled against ground conditions.


      <TABLE class=infoMacro><COLGROUP><COL width=24><COL></COLGROUP><TBODY><TR><TD vAlign=top></TD><TD>Quick links</TD></TR></TBODY></TABLE>

      The Lake Grassmere earthquake has a magnitude of 6.6. It occurred just after 2:30 pm on Friday afternoon, and was centred 8 km under the north-east of the South Island. The focal mechanism shows it to be a strike-slip earthquake, similar to the M6.5 earthquake in July. We have now had two similarly-sized earthquakes with the same sort of characteristics - they are termed a "doublet". This is not what we would usually expect.


      There will be an aftershock sequence to follow this earthquake, and we already have had several over magnitude 5. The revised forecast for a further magnitude 6 or greater, for the next 24 hours from 5:30 pm 16 August, is 28%. See the updated the statistics table.

      GeoNet response
      • Seismometers had already been deployed after the July earthquake, and these will have recorded this new sequence as well.
      • A GNS scientist will travel to the South Island tomorrow to check for any changes to the surface geology.
      • A landslide overflight and a survey of any liquefaction is planned for next week.

      The full set of accelerograph data for the Lake Grassmere earthquake, together with PDFs of the waveforms, are available from the GeoNet strong-motion FTP site, step by step instructions are located here. Data files are in ASCII format, and relevant documentation for decoding the files and descriptions of site conditions may be found in Also, you can see a summary spreadsheet of recorded accelerations and their locations.
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