M 7.7 quake Mariana Isl .... NOW

[davenn]

M 7.7 - 32km SSE of Agrihan, Northern Mariana Islands

the P was is quite large on my seismo ... surface waves haven't arrived yet (0739 AEST 2139 UT)

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

Dave

 

[fresh_42]

7.7 is a lot. Is there a tsunami expected? A link to a news page?

 

[davenn]

7.7 is a lot. Is there a tsunami expected? A link to a news page?

I linked to the USGS and to my page
news pages are unreliable and never give the correct info ... they probably don't even know the event has happened

there's no tsunami warning or watch in effect at this time

 

[fresh_42]

I'm simply not bright enough to translate the figures into imagination. One map shows a settlement only a few hundred km away.
And the amount of water above 212 km sounds dangerous. At least as long as one doesn't know the direction of movement.

 

[davenn]

One map shows a settlement only a few hundred km away

which map ? link ?

And the amount of water above 212 km sounds dangerous.

not sure what you mean by this ?
Dave

 

[fresh_42]

which map ? link ?

http://earthquake.usgs.gov/earthquakes/eventpage/us100068jg#shakemap

not sure what you mean by this ?
Dave

You're right. I misread the units. I thought it was closer to the surface. My fault.

 

[davenn]

You're right. I misread the units. I thought it was closer to the surface. My fault.

the 212km is the depth below the surface that the focal point of the quake is ( doesn't include sea depth if event is at sea like this one)

initially it was listed at 188km deep. and knowing the location, it's easy to realize that it is a subduction event.
In that area, the Pacific Plate seafloor is diving down under the Philippine Plate

One thing that will probably be noticed over the next 24 hours is that there is unlikely to be many aftershocks.
This is common with deep events, even large ones. If it was a shallow (crustal event, 0 - 30km deep) then there would be 100's
to 1000's of aftershock recorded. I will be surprised if there is anything more than a few 10's of aftershocks recorded, if that.
Dave

 

[davenn]

OK here's the raw seismogram

 

[Astronuc]

Just for background, "The Challenger Deep in the Mariana Trench is the deepest known point in Earth's oceans. In 2010 the United States Center for Coastal & Ocean Mapping measured the depth of the Challenger Deep at 10,994 meters (36,070 feet) below sea level with an estimated vertical accuracy of ± 40 meters," according to Geology.com. That's at most 11 km.
http://geology.com/records/deepest-part-of-the-ocean.shtml
http://www.deepseachallenge.com/the-expedition/mariana-trench/

The deeper the earthquake, the less likely a tsunami.

The 2011 earthquake off the Pacific coast of Tōhoku was a 9.0 magnitude (Mw) undersea megathrust earthquake occurred on 11 March 2011 at 14:46 JST (05:46 UTC) in the north-western Pacific Ocean at a relatively shallow depth of 32 km (19.9 mi), with its epicenter approximately 72 km (45 mi) east of the Oshika Peninsula of Tōhoku, Japan, lasting approximately six minutes.
https://en.wikipedia.org/wiki/2011_Tōhoku_earthquake_and_tsunami
http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2011/20110311.php
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/#details (page may be discontinued in the future)
https://www.ngdc.noaa.gov/hazard/11mar2011.html

Much of the Pacific Ocean is about 5-6 km deep.
http://oceansjsu.com/105d/exped_mapping/13a.html

 

[davenn]

and a processed seismogram with data

 

[anorlunda]

Thanks for sharing @davenn . Is there a layman explanation of how the data reduction from raw to processed works?

 

[davenn]

Thanks for sharing @davenn

you are welcome ... one of my loves in life

Is there a layman explanation of how the data reduction from raw to processed works?

ohhh ... where do I start ?

firstly, I didn't write the software or design the hardware for my system. Credit for that goes to Larry Cochrane from California
who was one of the original members of the PSN ( Public Seismic Network) in the USA.
http://psn.quake.net/

He designed 2 significant pieces of hardware a multi-channel preamp that goes between the sensors and the ADC data logger.
And the datalogger with its assoc software WinSDR (Windows Seismic Data Recorder)

preamp ... http://psn.quake.net/serialamp.html

ADC/Datalogger ... http://psn.quake.net/serialatod.html

WinSDR ... http://psn.quake.net/software.html#WinSDR

The raw seismogram you see in post #8 is a screenshot of the display on the WinSDR datalogging PC
currently I am using a Dell ( about 3 years old) and running Win7. This PC runs 24/7.

The analysis software that is on my main PC, for loading in and producing the final data file as seen in post #10
is called WinQuake ... http://psn.quake.net/software.html#WinQuake

WinQuake, along with the hardware and WinSDR have gone through many upgrades since its initial release in the early
- mid 1990's ( My station went digital in 1996)

have a read through some of the documentation in the links
hopefully it will answer most of your questions Regards
Dave

 

[1oldman2]

firstly, I didn't write the software or design the hardware for my system. Credit for that goes to Larry Cochrane from California
who was one of the original members of the PSN ( Public Seismic Network) in the USA.
http://psn.quake.net/

Very cool links and sites, thanks for posting them. I noticed when I used the link to your homepage that it came up blank, I know your site is up and running as I was looking at it yesterday, maybe the psn.quake site has a broken link to you ?

 

[davenn]

I noticed when I used the link to your homepage that it came up blank, I know your site is up and running as I was looking at it yesterday, maybe the psn.quake site has a broken link to you ?

yeah, the link on Larry's home page for my site is long out of date, he hasn't got around to updating it

just bookmark my homepage

http://www.sydneystormcity.com/cheers
Dave

 

[1oldman2]

Here is a link to some relevant info on Plate tectonics. http://phys.org/news/2016-07-earth-mantle-role-plate-tectonics.html