Hi Jim,  Thanks for this information.   I have one Lehman N/S and one =
E/W, and their performance agrees with your findings.  There may be =
differences due to orientation, but I do not see them.

Ted
  ----- Original Message -----=20
  From: Connie & Jim Lehman=20
  To: psn-l@.................
  Sent: Friday, May 30, 2008 11:25 AM
  Subject: Directional characteristics of a "lehman type" sensor-


  PSN friends--I have noted several references to directional =
performance on a typical 15-20 sec "Lehman" design.  It was our =
observation that very few quakes  were blocked out due to orientation.  =
One summer when mictoseisms are lowest (here in Virginia) we ran two =
systems with booms at right angles, N-S & E-W.  We copied 66 events in =
two months.  There were signatures in both orientations--(excepting for =
a half-dozen small events) and we noted the predictable comparisons with =
incoming P,S, & L wave fronts.  P waves show strong coming in broadside. =
 S waves show strongest coming in off the end.  Likewise the Surface =
waves -S show a distinctive difference whether they be Love waves or =
Raleigh.  You simply cannot hide from a readable event due to =
orientation.
     This test was made with systems having no filtering excepting to =
remove mechanical room noise typical in a building, and 60 hz AC.  We =
were satisfied the generalizations above were verified, as we copied =
several events (Alaskan or thereabouts--coming into our booms at 45 =
degrees) which appeared identical on our n-s,e-w readouts.  Running two =
long period systems is a luxury now, but in earlier days of the big =
bulky worldwide sensors, dual copy was standard--with few stations to =
get a tag on direction of event.
    Here in VA. we usually ran our system broadside a few degrees off =
E-W to accent the events of South Pacific, but any South American events =
of size would boom right in with lower P waves and heavy S wave =
signatures.
     Another side effect of noting amplitude of S or surface wave =
arrivals--one can tell whether the event has a shallow focus--less than =
30 km, or a deep focus of several hundred km--even before you are told!!
     I hope this is informative.  Jim Lehman







Hi Jim,  Thanks for this=20
information.   I have one Lehman N/S and one E/W, and their=20
performance agrees with your findings.  There may be =
differences due=20
to orientation, but I do not see them.
 
Ted

  
----- Original Message ----- 
  From:=20
  Connie &=20
  Jim Lehman 
  
To: psn-l@.............. 
  
Sent: Friday, May 30, 2008 =
11:25 AM
  
Subject: Directional =
characteristics of a=20
  "lehman type" sensor-
  


  
PSN friends--I have noted several =
references to=20
  directional performance on a typical 15-20 sec "Lehman" design.  =
It was=20
  our observation that very few quakes  were blocked out due to=20
  orientation.  One summer when mictoseisms are lowest (here in =
Virginia)=20
  we ran two systems with booms at right angles, N-S & E-W.  We =
copied=20
  66 events in two months.  There were signatures in both=20
  orientations--(excepting for a half-dozen small events) and we =
noted the=20
  predictable comparisons with incoming P,S, & L wave fronts.  =
P=20
  waves show strong coming in broadside.  S waves show =
strongest=20
  coming in off the end.  Likewise the Surface waves -S show=20
  a distinctive difference whether they be Love waves or =
Raleigh.  You=20
  simply cannot hide from a readable event due to =
orientation.
  
   This test was made with =
systems=20
  having no filtering excepting to remove mechanical room noise =
typical in=20
  a building, and 60 hz AC.  We were satisfied the generalizations =
above=20
  were verified, as we copied several events (Alaskan or =
thereabouts--coming=20
  into our booms at 45 degrees) which appeared identical on our n-s,e-w=20
  readouts.  Running two long period systems is a luxury now, but =
in=20
  earlier days of the big bulky worldwide sensors, dual copy was=20
  standard--with few stations to get a tag on direction of =
event.
  
  Here in VA. we usually ran our =
system=20
  broadside a few degrees off E-W to accent the events of South Pacific, =
but any=20
  South American events of size would boom right in with lower P waves =
and heavy=20
  S wave signatures.
  
   Another side effect of =
noting=20
  amplitude of S or surface wave arrivals--one can tell whether the =
event has a=20
  shallow focus--less than 30 km, or a deep focus of several hundred =
km--even=20
  before you are told!!
  
   I hope this is =
informative. =20
  Jim Lehman
  
  =20