Interesting.

Thanks Bob.
putting these sites in my favorites.

Best Regards,
geoff

----- Original Message ----- 
From: "Bob Hancock" 
To: 
Sent: Monday, March 29, 2010 5:28 PM
Subject: Re: Un Regards to: 100328.213800.rb1.psn


Hi Geoff -

You are correct that three channels can get distance with the S-P time and using charts, you an get magnitude if your equipment is 
properly calibrated, and you can determine direction, assuming you can get the initial P wave motion off of all three channels and 
one of the channels is on a null.  Depth is dependent upon receiving certain waves (pP-P), and if for some reason they are not 
visible you might not get depth.

As for a visualization of the fault plane, you need to reference the focal mechanism (beech ball) for the event.  There are three 
variables,  Strike, Dip, and Rake.  Following are some definitions I have found useful for me to understand the concepts:

Strike - the fault-trace direction in decimal degrees (0 to 360, relative to North), defined so that the fault dips to the right side 
of the trace. That is, the fault always dips to the right when moving along the trace in the strike direction (from one point to the 
next). This means that the hanging-wall block is always to the right. This is important because rake (which gives the slip 
direction) is defined as the movement of the hanging wall relative to the footwall. For a vertical, strike slip fault (for which 
"hanging wall" has no physical meaning) we still call the right-side block the hanging wall to distinguish between right lateral and 
left lateral motion.

Dip - the angle of the fault in decimal degrees (0 to 90, relative to horizontal).

Rake - the direction the hanging wall moves during rupture, measured relative to the fault strike (between -180 and 180 decimal 
degrees). Rake=0 means the hanging wall, or the right side of a vertical fault, moved in the strike direction (left lateral motion); 
Rake = +/-180 means the hanging wall moved in the opposite direction (right lateral motion). Rake>0 means the hanging wall moved up 
(thrust or reverse fault). Rake<0 means the hanging wall moved down (normal fault).

This information is listed on the USGS notifications that are contained in their list of recent events under "Scientific & 
Technical" and denoted by a colored beech ball.  They are listed under "Best Double Strike Couple."  There are two listings NP1 and 
NP2.  NP1 is assumed to be the axis that slipped and NP2 is the secondary axis.

To find focal mechanism of older events you need to reference the Global Centroid Moment Tensor catalog at the following address:
 http://www.globalcmt.org/CMTsearch.html

To translate these three numbers Strike, Dip, & Rake into a visual graphic, I use the following program written by Prof Charles 
Ammon at Penn State University:
http://eqseis.geosc.psu.edu/~cammon/Java/fmech.html

This is a Java based program and you will need the Java Run Time Environment on your computer to make it work.

An alternative program that I have also used that has lesser limitations, but does not require the Java Run Time Environment was 
written by Prof George Helffrich in the UK:
http://www1.gly.bris.ac.uk/~george/focmec.html

Cheers,

Bob Hancock
Three Points, AZ






On Mar 29, 2010, at 4:46 PM, Geoffrey wrote:

> Then i understand that with three channels you can
> with a single station get distance, magnitude and direction as
> well as focal depth ??
>
> For best results Id hazard a guess that
> all data must be taken in synchronous fashion
> meaning all three channels are sampled simultaneous at the very same rate.
>
> And, is there any program to
> take such data and recreate a three dimensional picture
> showing angles and the absolute magnitude.
> There really is motion only in one direction
> but it seems you must have three different
> channels ro recreate that absolute motion in
> whatever direction ???
>
> It seems to me that to recreate reality all known physical dimensions must be recorded
> simultaneously.
>
> You know what this says about everyday life ???.
> One rarely sees or senses reality.
> :-)
> Thanks for your reply.
> It opens my mind a bit.
>
> Best Regards,
> geoff
>
>
>
>
> ----- Original Message ----- From: "Bob Hancock" 
> To: 
> Sent: Sunday, March 28, 2010 10:37 PM
> Subject: Re: Un Regards to: 100328.213800.rb1.psn
>
>
> Hi Geoff -
>
> With the two horizontal channels,and the initial direction of the P wave on each channel, you can achieve a great circle course 
> line, but you will not know which side of the receiving station that the event occurred.  To do that you also need the initial 
> direction of the P wave on the vertical channel.
>
> Bob Hancock
> Three Points, AZ
>
>
> On Mar 28, 2010, at 10:22 PM, Geoffrey wrote:
>
>> Wouldn't it be possible to somehow derive a bearing
>> or angle of incidence somehow relating to the
>> differences between the N/S and the E/W signals
>> in this EVENT posted to PSN database ?
>>
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