First respectable quake for 2014

[davenn]

in the early hours of this morning ( my time) 1603Hrs UT i recorded the first sizeable quake of the new year.
This was a Mw 6.6 in the northern Vanuatu Islands. quite a deep event at 196km

the event will still be visible here on my online seismogram for the next ~ 20 hrs from the time of this post.

cheers
Dave

 

[phinds]

Well, that didn't take long. Glad to see Mother Earth is alive and kicking in 2014. Also glad I don't live right next to the epicenter.

 

[litup]

Well, that didn't take long. Glad to see Mother Earth is alive and kicking in 2014. Also glad I don't live right next to the epicenter.

Be glad you aren't at the epicenter for no other reason than it is pretty hot 200 km underground:)

One question: How do you tell the location of the quake from this one graph? Don't you have to triangulate and such with several readings hundreds of miles apart?

 

[davenn]

hi you litup

that's correct, from one seismogram the location cannot be worked out, only the distance and that is a little variable until the depth of the event is worked out. Increasing depth makes the quake look closer than it really is.
That is because the direct line path from the quake focus is shorter than the path across the curved surface of the Earth from the quake epicentre. The epicentre point is of course the point on the surface directly above the focus.

The info for the quake comes from the USGS WWSSN (World Wide Standard Seismic Network) ( also known as the GSN Global Seismograph Network) and I plug that data into my ( Not created by me!) analysis program to produce what you see above.
The analysis prog, Winquake, is very versatile with full FFT, filtering, depth tables etc adjustments

the recorders don't have to be 100's of km's apart, recorders closer into the event is good for determining locations of local and regional events. Of course for these teleseismic events, the recorders used to locate the event are often 1000's of km's apart

cheers
Dave

 

[phinds]

Be glad you aren't at the epicenter for no other reason than it is pretty hot 200 km underground:)

As Daven has already pointed out, you misunderstand the definition of epicenter.

 

[davenn]

hi you phinds

"Mother Earth" is still really quiet, that quake is still the only one above M6.0 since the beginning of the year.
recorded a few high 5's ... a couple in the south Pacific area and a couple around coastal Chile and some other M 5- 5.5 events that only produced tiny wiggles on the recorder

At this time each year I sit back and wonder when the M8+ for the year will strike and where will it be ? ...
Its one of those things, you know its going to happen, just don't know where and when. Some years there isn't a M8+ and other years like the last two, 2012 and 2013 there were in each year two M8+ events.
Over the long period, the last ~ 120 years since recording began, the avg. is still one M8+ per year.

cheers
Dave

 

[litup]

Thanks for pointing out the difference between epicenter and focus! I had some sense of what was going on from my work at AUTEC on Andros island, where pingers on subs or torpedo's would spread its sound pulses to hundreds of hydrophones both buried on the bottom of TOTO (Tongue of the ocean, on the east side of Andros) and hydrophones suspended on cables going down to the bottom some 8000 feet deep.

After work, I could go into the control room and switch in anyone of the hydrophones and feed the sound to an amp and speaker. That was incredible. The sounds down there were like being on another planet, whoops and hoots of dolphins and whales and such 24/7. Google TOTO and AUTEC, you can see what I am talking about!

 

[phinds]

Over the long period, the last ~ 120 years since recording began, the avg. is still one M8+ per year.

Wow ... I didn't realize it was that often. I was thinking more like 2 every 5 years. Guess I haven't been paying attention.

 

[davenn]

OK finally another M6+ must have spoken into being
a Mw 6.5 off shore the northern coast of Puerto Rico

its coming in on my live seismo NOW http://www.sydneystormcity.com/seismograms.htm

the quake is 1/2 way around the world from me, so its taking time for all the parts, P, S and surface waves to get to my recorder

cheers
Dave

 

[jbrussell93]

that's correct, from one seismogram the location cannot be worked out, only the distance and that is a little variable until the depth of the event is worked out.

Is triangulation really the only way? I've heard that you can actually estimate the epicenter using only a single seismometer. Determine the direction/angle of the incident p-wave by looking at the various components (tells the direction to epicenter), and then estimate the distance from the seismometer to the epicenter.

 

[davenn]

Is triangulation really the only way? I've heard that you can actually estimate the epicenter using only a single seismometer. Determine the direction/angle of the incident p-wave by looking at the various components (tells the direction to epicenter), and then estimate the distance from the seismometer to the epicenter.

Im not aware of anything ... if you can throw up some links to papers I would enjoy reading


its what I was taught at university, but hey, that was 15 - 20 yrs ago

cheers
Dave

 

[jbrussell93]

Im not aware of anything ... if you can throw up some links to papers I would enjoy reading


its what I was taught at university, but hey, that was 15 - 20 yrs ago

cheers
Dave

Hmm... after searching for a bit, I couldn't find anything in the literature. My information is coming from a plate tectonics professor (seismologist) who made sure to share with us that, in principle the epicenter can in fact be ESTIMATED using only 1 station. We even had to do this on our midterm.

He said that even though it can be done in theory, no one would ever just use a single station to locate an earthquake. It probably isn't all that accurate.

I know that there are many other techniques for locating earthquakes such as double difference [http://www.ldeo.columbia.edu/~felixw/papers/Waldhauser_Ellsworth_BSSA2000.pdf] though the details are mostly beyond me...

 

[davenn]

hi there

thanks for the link
yeah pretty heady reading for me too haha
I would need some one knowledgeable to walk me through the method in a way I could understand

I guess it boils down to if there were easier ways than triangulation, they would be getting used.
Since triangulation is what is used in every seismo observatory, its still the best and quickest way to get a location, considering there's no lack of stations from which to derive data.

cheers
Dave

 

[Squatchmichae]

This appears to be a slightly old thread, but I will respond:
Using a single three-component seismometer, it is possible to crudely estimate the location of an earthquake if a p-wave and s-wave are clearly recorded. By computing the polarization vector of the incoming p-wave from the cross-component covariance matrix, you can get the direction back to the source. By computing the s-wave minus p-wave travel time, you can get the distance to the source (think of lightning and thunder). So with distance and direction, you have a location. With a non-homogenous medium, you need to trace the seismic raypath back from the polarization direction, but this is possible, in principle.