Another Megathrust event in Indonesia tonite

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Discussion Overview

The discussion revolves around recent seismic events in Indonesia, specifically a significant earthquake off the NW coast of Sumatera, which was initially recorded as a Mw8.7 and later revised to Mw8.6. Participants also mention an aftershock and other unrelated seismic activity in Mexico. The focus includes the analysis of seismic signals and the implications for tsunami generation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports ongoing significant seismic signals in Sydney, Australia, from the earthquake off Sumatera.
  • Another participant notes a Mw8.2 aftershock following the initial event, although the signal is difficult to analyze due to interference from the primary quake.
  • There is mention of a separate earthquake in Mexico, initially reported as Mw7.0 but later downgraded to Mw6.5, with observations on recording challenges due to environmental noise.
  • One participant expresses relief that the seismic events in Sumatera did not generate significant tsunamis, attributing this to the nature of the faulting involved.
  • Participants discuss the persistence of stress in the region despite previous large earthquakes, suggesting ongoing geological activity.

Areas of Agreement / Disagreement

Participants express a general sense of relief regarding the lack of significant tsunami risk from the recent events, but there is no consensus on the implications of the seismic activity or the ongoing geological conditions in the region.

Contextual Notes

Some participants note the challenges of recording seismic events due to environmental noise and the limitations of their equipment, which may affect the quality of the data collected.

Who May Find This Useful

Individuals interested in seismology, earthquake analysis, and the geological dynamics of tectonic plates may find this discussion relevant.

davenn
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hi gang

2 hrs after the event started to roll in on my seismograph, here in Sydney Australia, I am still recording a significant signal.

The quake is off the NW coast of Sumatera with almost an identical epicentral point as the 2004, Mw9+ event.
Tonite's event was initially listed as a Mw8.7 by the USGA and ~ an hr or so later was revised down to a Mw8.6.
I haven't seen any specific reports as yet other than comments to the effect that a tsunami was generated (USGS)

Dave
 
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This has been followed by another major event in the same area

a Prelim Mw 8.2 aftershock. I am finding it hard to see as the initial event is obscurring the signal a lot.
here is a compressed screen shot from my analysis program of the initial event...

attachment.php?attachmentid=46105&stc=1&d=1334144956.jpg


cheers
Dave
 

Attachments

  • 120411 Mw 8.6 offshr NW Sumatera1.jpg
    120411 Mw 8.6 offshr NW Sumatera1.jpg
    104.4 KB · Views: 665
another earthquake this time in Mexico 7.0...
 
meidan said:
another earthquake this time in Mexico 7.0...

latest data has it downgraded to a Mw6.5, still a respectable event
I didnt record it here in Australia, its usually got to be M7.0 and greater when from the western Americas ( USA down to Chile).
Its a real balancing act for me, I live in the suburbs with lots of manmade noise from clothes washing machines bouncing around on spin cycle to much heavy traffic on the road.

Keeping the gain of the system a bit lower can be a blessing in disguise as in the big events of last nite. Even at only 4500 km from the event, The M8.6 still maxed out my 14bit A to D converter ( time for a 24bit one haha). But not as bad as some of my fellow recording stations in the USA who's systems, with their much higher gain, were maxing out from almost the start of the event, even tho they were 4 x the distance from the epicentre as me.

cheers
Dave
 
Well it looks like Sumatera and the surrounding region really dodged a bullet last nite.
Both the events were a bit to the west of the downward thrusting slab of the Indo-Australian Plate. Their Centroid Moment Tensor solutions revealed that they were on strike - slip faults. This pretty much allieviated the possibility of any significant tsunami being generated. Everyone breathes a sigh of relief :)

Its still amazing that after 8 years, a Mw9.2 and a Mw8.7 (some months later), that so much stress was still pent up in the region.

Dave
 
It's great to have you here Dave.
 
awww thanks Evo :)

The subject is a bit of a passionate hobbyhorse of mine haha
has been for many years

I hope general discussion of events etc, like above, is within the guidelines of the forum rather than always just being specific question/answer type threads

cheers
Dave
 

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