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Major quake SW Pacific

by davenn
Tags: major, pacific, quake
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davenn
#1
Apr12-14, 03:52 PM
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coming in on my seismo NOW

Southeastern Solomon Islands

initially reported as a M 8.3, since dropped to a M 7.6
But its still maxing out my main channel ( maybe it will go back up to ~ 7.8 ?)

http://www.sydneystormcity.com/seismograms.htm


cheers
Dave
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davenn
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Apr12-14, 04:58 PM
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Have had a text message from a friend on holiday in Vanuatu. He is in the town of Luganville on the island of Santo ( nthrn Vanuatu). His location is ~ 710 km SE of the epicentre.

It was felt by those present as a rolling motion.

cheers
Dave
Astronuc
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Apr12-14, 07:05 PM
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http://earthquake.usgs.gov/earthquak...00phx5#summary

Location 11.315S 162.211E
Depth 29.3km (18.2mi)

Mag 7.6

davenn
#4
Apr13-14, 02:12 AM
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Major quake SW Pacific

Here's a screenshot before the signal started to overwrite the earlier trace



interesting that this event has so far not produced any large aftershocks

This is what the quake looks like once it has been saved and transferred into the Winquake analysis program

This is from a low gain channel that isn't maxing out the 16 bit AtoD converter




cheers
Dave
Attached Thumbnails
140412 2014UT M 7.6 SE Solomons annotated.GIF   140412.201808.zlo.psn.gif  
jim hardy
#5
Apr13-14, 10:54 PM
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Dave - i'm no earth scientist but have done a little looking at waves propagating in structures.

Are you located fairly close to that earthquake ?
davenn
#6
Apr14-14, 04:24 AM
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hi there Jim

Well sort of .... 2700 km's ... just up the road from me ( in the big scheme of things)

in the previous post of mine ... the second image ( the one from the analysis program)
look at the bottom line (immediately above the gram) starting with Org:
Org: = Origin time = 20:14:39 UT
P: = P wave arrival = 20:19:57.8 UT
S: = S wave arrival = 20:24:14.4
Diff: = S-P difference = 4 mins 16.6 sec
Dist: = Distance = 24.60 Degrees = 2734.9 km = 1699.4 miles
Mag: = magnitude 2 given -- ML = Local Magnitude and MS = Surface Magnitude
and finally
JB: = Jeffreys-Bullen Tables
WinQuake maintains three sets of P and S wave travel-time tables. Two are Jeffreys-Bullen (JB) tables, one set for teleseismic (distant events) and the other for regional or local events. The third set of tables use the IASP91 model of the earth. These tables are used to calculate the distance and the time of origin of the event. They are also used to calculate the location of the P and S markers if the event time and location are known.

From the Org and P info, you can see that the P wave took a little over 5 minutes to get to me

Ohhh and speaking of ML = Local Magnitude and MS = Surface Magnitude
ML was the original Richter magnitude scale Developed my Charles Richter and Beno Gutenberg at CALTECH in the 1930's. It was designed to be used with a particular style of seismometer, the Californian geology and for quakes out to ~ 100 km from the recorder.
It got hijacked by seismological institutes worldwide and adapted for their local geology and seismograph types
It uses the S-P time and the measurement of the amplitude of the largest waves on the seismogram ( in millimetres)
MB = Body wave magnitude using the maximum amplitude of the "body waves ( the P or S waves)
MS = is the Surface wave magnitude using the maximum amplitude of the "surface waves"
This is great for big shallow events, but useless for deeper events where the surface waves are very low amplitude. As you could now guess, the presence of large amplitude surface waves is a good indication of a
shallow < 50km event.

hope that's of help

I'm not so happy that over nite ( Sunday-Monday) there was a M 7.4 aftershock that I recorded but the datalogger software for some reason wont let me save the event data, so the only record of it that I have is the screen dump of the seismogram.

cheers
Dave
jim hardy
#7
Apr14-14, 09:18 AM
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WARNING - Boring Anecdote Alert

Thanks Dave. That's informative, and interesting links.

As i said i'm no earth scientist
Years ago while trying to track down a tinkling we were hearing over the "Loose Parts Monitor" in a nuclear plant i quite by accident stumbled across an old geology textbook
At the time nukes were basing loose parts localization solely on amplitude. We'd made several entries into the steam generator looking for dents.
The chapter on seismology was the breakthrough i needed - to appreciate various waves and their velocities.
Armed with meager understanding of the wave shapes due to different arrival times of surface vs compression waves, we quickly isolated the "tinkles" to a harmless feedwater check valve flapper and not something clanking around inside the steam generator.

I've wanted to thank a seismologist ever since.
Thank you.

The serendipitous appearance of that old textbook was one of those 'little daily coincidences' that are miracles in disguise.

hope this wasn't too boring,
Sorry for off topic,
old jim
davenn
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Apr15-14, 05:54 AM
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Hi Jim

That's a cool story I always enjoy hearing about what others have been involved with

Gosh, I will never claim to be an expert haha just a very passionate amateur
Tho I worked my way through a BSc in geology, I have never "worked"
in the field .... I have been an electronics service tech/telecoms tech for various companies all my working life

I have been able to create a nice blend of seismology and electronics over the years, sourcing/building sensors, experimenting with various low noise/high gain preamps, and different A to D circuits

cheers
Dave


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