• time: 00:01:05 AST
  
• Location:
  
• earth quake:19.1385N, 66.8231W  (82.19 Km north-northwest of Arecibo)
  
• ao: 18.344289N 66.752778W
  
• Depth: 36 km

• Each line is  15 minutes section. AST labels on left, UTC labels on right.
  
• 13jan14 BNZ (vertical motion 10-80hz) plot (.pdf)
• 13jan14 HNZ (vertical motion 80-250hz) plot (.pdf)
• plot from juan carlos morales..vertical, and ew, ns horizontal accelerations (.jpg)
  
• iris plot of earthquake (.pdf)
• plot scale: 4.379e6 nM/sec (nanoMeters/sec)

• Page 1:
• The horizontal scale is seconds from the start of the earthquake (at the epicenter). (+/- 1000 seconds).
  
• Top: telescope azimuth before and after the quake.
• 2nd: gregorian zenith angle during the quake.
• 3rd: tiedown tensions during the quake
• black: td12, red td4, green td8
• You can see the tensions begin to oscillate about 30 seconds after the quake (at epicenter).
• Bottom: total tiedown tension on the platform during the quake.
• The tiedown jacks were stationary during this time period.
• The total tension will change as the temperature changes (at midnight this happens very slowly).
• The average tiedown tension dropped by 800 lbs from before to after the earthquake.
• Page 2:  blowup of tiedown tensions
• tension in the 3 tiedowns
• total tension in the 3 cables
• The tension in the tiedowns went from 132.23 to 131.42 Kips (a reduction of 800 lbs).
• Page 3 oscillation frequencies.
• data from times 28 to 151  seconds was transformed to measure the oscillation freq.
• Data was sampled at 1 hz (making the maximum bandwidth .5 hz).
  
• The 3 colors are td 12 white, td4 red, td8 green.
• The strongest frequency was at .460 Hz i td 8.
  
• From previous hurricane measurements, this is probably aliased from .54 hz.
• During hurricane georges a .57 hz freq was measured with the tilt sensors. It was the pitch direction (az arm tilting up and back).
• the azimuth was pointed at 49 degrees. this is about 10 degrees in azimuth from the td8 direction.
  
• .291, and .368 hz are also flagged. These were the frequencies seen during a previous earthquake.
  

Summary

• 6.4 magnitude quake occurred 00:01:05 ast on 13jan14
• The azimuth arm was pointing within 10 degrees of td8
• The strongest oscillation was .54 Hz in td8
• The total tension in the tiedowns dropped by 800 lbs after the earthquake.
• This has not been seen in previous earthquakes.
• Inspection of the cable from td 8 to the platform showed:
• the cable with the splice close to the tower had more than 8 strands broken were the cable hits the splice box (on the tower side).
• This is the same cable that had its hairpin cut during the upgrade
• The drop in tension was probably caused by the cable relaxing when the strands popped.
  

up to oscillations
 home_~phil