Quake Watch 2012

reply to post by muzzy


From the IRIS Education and Outreach PDF file on how earthquakes are located we get

From observing and analyzing many earthquakes, we know the relationship between the S-P time and the distance between the station and the earthquake. We can therefore convert each measured S-P time to
distance. A time interval of 1.5 minutes corresponds to a distance of 900 kilometers, 3 minutes to 1800 kilometers, and 5 minutes to 3300 kilometers.

Google has recently started obfuscating their links to pdf files with masses of irrelevant information, presumably concerned with the gathering of intel, and making it impossible to copy a proper link to pass on, however the link in green below their rubbish should work. - www.mgs.md.gov...

Another broken down step by step version of this can be found here

Note that they are in effect quoting 10 km/sec as the interval speed on the assumption that these waves always travel at the same speed. They do not. That is a major simplification. The further away from the event the more likely you are to get attenuation of the signal and damping of the speed. In addition to this not all strata in the earth pass the signal at the same speed and indeed the signals going through the earth centre change considerably.

In order to illustrate what I am saying download and have a read of this article which contains this abstract: (I have removed all Googles rubbish from that link so hope it works)

The hypocenters of 43 earthquakes on Kilauea Volcano were analyzed in detail in order to examine the accuracy of hypocenters determined with data from tripartite arrays and to look for evidence of zones of abnormally high or low velocity in a region of complex crustal structure. Ten vertical and two horizontal seismometers were operated on the south flank of Kilauea within the seismic network of the Hawaiian Volcano Observatory. A number of combinations of the temporary stations were treated as separate tripartite arrays. The sides of each tripartite array were 1 to 2 km long. Azimuths and apparent velocities of P-wave fronts observed at these arrays generally agreed well with the values predicted from hypocenters calculated using data from as many as 20 stations. Some observed azimuths differed from the predicted values by over 40° and some apparent velocities differed by nearly a factor of 2. These differences are consistent with the travel-time residuals found when the hypocenters are located with all available data. They can be attributed to local zones of abnormally high or low velocity or to changes in the thicknesses of the assumed crustal layers. Waves that travel through the east and southwest rift zones arrive relatively early and the waves traveling through the Kaoiki fault zone arrive late. Refraction data were compiled to obtain a new average crustal structure. When small tripartite arrays are used to locate shallow earthquakes, a crustal structure with a linear increase in velocity should be assumed in order to calculate unique hypocenters and to obtain less scatter in a group of hypocenters.

This article on Earthquake Location Accuracy (Google rubbish removed) says in it's abstract

Abstract Earthquake location catalogs are not an exact representation of the true earthquake locations. They contain random error, for example from errors in the arrival time picks, as well as systematic biases. The most important source of systematic errors in earthquake locations is the inherent dependence of earthquake locations on the assumed seismic velocity structure of the Earth. Random errors may be accounted for in formal uncertainty estimates, but systematic biases are not, and they must be considered based on knowledge about how the earthquakes were located. In this article we discuss earthquake location methods and methods for estimating formal uncertainties; we consider systematic biases in earthquake location catalogs; and we give readers guidance on how to identify good-quality earthquake locations.

It is also a good read. (30 pages) Page 28 however contains the answer to your dilema Muzzy.

Sorry - run out of space. See next post

Global centroid catalogs are also sometimes used in statistical studies. The earthquake centroid, the center of moment, is often offset rom the hypocenter by several 10s of km or more, so the locations from the centroid catalogs are not directly comparable to hypocenter location catalogs. It is important to choose the catalog appropriate for the scientific question at hand: if one is interested in where earthquakes nucleate, a hypocenter catalog is preferable; while if one is interested in where the most slip occurs, a centroid catalog is more appropriate. The location uncertainty of centroid catalogs is similar to that of other global location catalogs.

reply to post by Doodle19815


I took a look but don't think it worth getting involved. Not impressed by her description of herself.

3 hours? By boat, train, plane, pony express, shank's pony, as the crow flies?

If we consider an average of 30 mph or 48 kph then 3 hour would be 144 km or ~14 seconds for the waves. @2 hours only 96 km or ~9 seconds. Depending on the geology of the area it is indeed possible for her to have felt a 2.6. But moved the couch? Not so sure about that.

The other problem is that the time of the earthquake suggested was Monday, September 03, 2012 at 07:12:32 AM at epicenter so not exactly late at night on Saturday.

I was sitting on my duff Saturday night

Hi PM,

U being one of the most LEVEL HEADED ones around here, I wonder whether you concur with some or all of the following?

There are now five regions of the world where seismic tension is registering higher than normal: California, the Virgin Islands of the Caribbean plate, Alaska, the Philippines, and Indonesia. Any of these regions are primed for the eruption of large-scale seismic events. People in high-risk seismic zones should remain alert for the potential occurrence of potentially hazardous seismic or volcanic episodes./ex]

edit on 5-9-2012 by SpaceJockey1 because: Oops spelling

Earthquake Details

This event has been reviewed by a seismologist.
Magnitude
7.6
Date-Time
Wednesday, September 05, 2012 at 14:42:10 UTC
Wednesday, September 05, 2012 at 08:42:10 AM at epicenter
Location
10.120°N, 85.347°W
Depth
40.8 km (25.4 miles)
Region
COSTA RICA
Distances
60 km (38 miles) SSE (167°) from Liberia, Costa Rica
127 km (79 miles) SSW (209°) from San Carlos, Nicaragua
141 km (88 miles) W (276°) from SAN JOSE, Costa Rica
Location Uncertainty
horizontal +/- 13.6 km (8.5 miles); depth +/- 6.2 km (3.9 miles)
Parameters
NST=737, Nph=737, Dmin=135.8 km, Rmss=1.42 sec, Gp= 18°,
M-type=(unknown type), Version=F
Source
Magnitude: USGS NEIC (WDCS-D)
Location: USGS NEIC (WDCS-D)
Event ID
usc000cfsd

USGS

Oh My

7.9 3km NE of Samara, Costa Rica 2012-09-05 14:42:10 9.900°N 85.500°W 46.0

Source

Just saw that... not even 5 minutes before I was looking at the real time quake map. Stepped away to get some breakfast and boom. This is tragic. Praying for all those in the area. Please no tsunami....

reply to post by SpaceJockey1


Can you give us the source for this? Thanks.
My heart goes out to all people in the affected area.

It looks like this earthquake was originally reported offshore and a bit deeper. Now USGS shows the epicenter on land and only 20km deep.
So, we shouldn't expect a tsunami, but the shaking was potentially life-threatening.
Still waiting on Pager info...

reply to post by PuterMan


Thank you Puterman--bookmarked the direct last-page link.

on reuters and usgs tsunami watch in effect

Tsunami from this quake in Costa Rica not likely, quake is about 8km inland from sea shore. Very shallow and only 8 km from the very beautiful Samara. Depends on the movement directions, this could have caused some severe damage and possibly life lost. Fortunately not high population (Include tourist probbaly around 10,000) neither high buildings. At this early morning time, most people would be up and around as well.

000
WEHW42 PHEB 051451
TIBHWX
HIZ001>003-005>009-012>014-016>021-023>026-051651-

TSUNAMI INFORMATION STATEMENT NUMBER 1
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
451 AM HST WED SEP 05 2012

TO - CIVIL DEFENSE IN THE STATE OF HAWAII

SUBJECT - TSUNAMI INFORMATION STATEMENT

THIS STATEMENT IS FOR INFORMATION ONLY. NO ACTION REQUIRED.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 0442 AM HST 05 SEP 2012
COORDINATES - 9.9 NORTH 85.5 WEST
LOCATION - OFF COAST OF COSTA RICA
MAGNITUDE - 7.9 MOMENT

EVALUATION

THE PACIFIC TSUNAMI WARNING CENTER HAS ISSUED AN EXPANDING
REGIONAL TSUNAMI WARNING AND WATCH FOR PARTS OF THE PACIFIC
LOCATED CLOSER TO THE EARTHQUAKE. AN EVALUATION OF THE PACIFIC
WIDE TSUNAMI THREAT IS UNDERWAY AND THERE IS A POSSIBILITY THAT
HAWAII COULD BE ELEVATED TO A WATCH OR WARNING STATUS.

IF TSUNAMI WAVES IMPACT HAWAII THEIR ESTIMATED EARLIEST ARRIVAL
TIME IS

0243 PM HST WED 05 SEP 2012

THIS WILL BE THE ONLY STATEMENT ISSUED FOR THIS EVENT UNLESS
ADDITIONAL DATA ARE RECEIVED.

Source

Revised magnitude, location, and depth again.

Preferred Location Parameters
Magnitude
7.6 Mww

Location
10.120°N, 85.347°W
± 13.6 km

Depth
40.8 km
± 6.2 km

REVIEWED
Event ID
usc000cfsd

Data pulled from USGS technical page.


ETA:
Pager info now posted.
Thankfully the magnitude has come down and the estimated population exposed to the highest intensity shaking is relatively low (32k).

Hmmm... quite near the opposite point on Earth from the previous 7+ quake in Phllippines.

All my family is there. Phones were down but I was able to contact a cousin via FB chat. She is near the capital and she said it was felt very strong there. I finally saw a post from my mother on FB so I think both her and my dad are fine. I'm waiting to see what the damage was though!

reply to post by Aromaz


Opposite and just as strong at the end of geomagnetic storm. Large sunspot growing at incredible speed. Connection?

reply to post by favouriteslave


You were the first person I thought about when I opened the comp and saw the news. Take good care and know my prayers are with your family.

reply to post by SpaceJockey1


Only just come back in to find this one. I guess as far as your comment goes it depends who was the source. I am not sure that I would agree with all of those areas.

There are now five regions of the world where seismic tension is registering higher than normal:

California, - no the current activity is cyclical and normal
the Virgin Islands of the Caribbean plate, - so there is/was a small swarm. Not particularly significant. Vanuatu will kick off before that area. See the Virgins....

Alaska, - may be volcanic therefore not relevant
the Philippines, - well it was but that rather unusual Mag 7 may have cured that for a while
and Indonesia. - and always Indonesia. Where is the additional activity over and above the normal? I won't put up a chart for that as 'Indonesia' does not define the area properly, but when I do put in Indonesia for this year guess what? I get the normal straight line. There happens to have been a slight increase yesterday, but it doe not affect the graph.

And what is normal? Normal now, normal in the 1980s, normal in the 13th century, normal in 20,000 BCE - oh right, of course normal as defined the the extremely short term collective Internet memory. Pssssssh!

Bit like the stock market - the share prices are rising, the share prices are falling all for the sake of a few points of an hour or two. Look at the bigger picture, the longer history. One day of a slight increase does not an increase in seismicity make.

I see GFZ Potsdam have the Costa Rica as 7.4.

Okay so everyone is fine as far as I know. I talked to my cousin via FB and she said it was felt strongly there and finally a post from my mother and a call from my father. He described it from the second floor of their house as a "fun ride" But if you have ever been there you know most housing is built to withstand earthquakes of this size! So far all my family is ok but my cousin took pics of a road in Alajuela that is impassable due to Rock/landslide. My mom said this "Diana if you tried calling and couldn't get through its probably because your dad was on the phone talking to faily. So far the phones are working within the country. The house was really swaying and a few things in the house were swinging back and forth. It seemed like more than 40 seconds. It scared the crap out of the dog. There were after shocks in Cartago, but we didn't feel them here...Mom"



www.facebook.com...

and

www.facebook.com...

reply to post by prophetboy12


There are currently no large sunspots. It is the internet memory thing again. What is currently on the Sun is extremely small especially since we are so close to Solar Max. Here is a big one There is currently nothing anything like that. (And here is another)

I have been keeping the records for sunspots and earthquakes for some time no a still cannot see a provable connection beyond circumstance. (Which does not mean I do not believe it, just that I can't prove it)