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Intro:

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All links:

• 07jan20: 6.4 quake (and related quakes). 
• telescope motion 
• td tensions, tilt sensors
  
• 23sep19: td tensions during 6.0 earthquake.
  
• 19sep19: tracking 3C273 with sbh with a large pointing error.
  
• 13jan14: 6.4 magnitude earthquake north of arecibo. tiedown tension variations.
  
• 16may10: 5.8 magnitude earth quake 34 km from AO. tiedown tension variation.
  
• 11mar09: earthquake causes td8 tension to vary.
  
• 11mar06: oscillations seen in cbh total power while tracking the crab.
  This shows many oscillation frequencies. Those measured during the hurricanes plus a few others. The interesting thing is that some of the oscillation frequencies are changing with hour angle (az,za) as we track the source (the .55 hz frequency seen during the hurricanes changes with az,za while the .35 Hz does not).
• 1.2 Hz oscillations caused by the refrigerator crossheads.
• 19may05: lbw
• 17oct04: sbn
• 29sep04: cband
• 15sep04: platform oscillations measured during tropical storm jeanne
  This used the load cell on Td12 (1hz). The other tiedowns had lost power.
• 12aug04: technicians felt large oscillations in the dome while tracking at low za.

This may have had something to do with the hydraulic brakes which require large torques to move downhill at low za (since there is no gravity).
• 21sep98: platform oscillation frequencies measured during hurricane georges:
  This used the tilt sensors in the dome (5 hz sampling) and the tiedown load cells (1hz).

Tiedown cable tension &  tilt sensor response to earthquakes

    The table and plots show the response of the tiedown load cells and tilt sensors in the dome  to various earthquakes.

• The tiedown cable tension data is always available. It is sampled at 1 hz
• There are  2 tilt sensors on the rotary floor in the dome.
  
• The pitch tilt sensor is along the azimuth arm direction. It goes +/- 10 degrees
• the roll tilt sensor is perpendicular to the azimuth arm direction. I think it goes +/- 2 degrees.
• the tilt sensors are normally not run. I started them 9jan20 after the large earthquakes.
  

A description of  tiedown cable tension plots:

•  Page 1: Tiedown tensions  each load cell around the earthquake.
• Black is loadCell 1, red is loadCell 2
• The blue line is the time of quake at the epicenter
• The horizontal axis is seconds from the quake (at the epicenter).
• It starts 60 seconds before the epicenter time to 300 secs after the epicenter time.
  
• The vertical scale is tension (kips) in each td cable.
  
• The 2 load cell values should be the same. Offset are usually dcOffsets in the amplifier.
• If a there is only one line in a plot, that implies one of the loadcells was bad. In that case i duplicated the good one.
• Page 2:
• top: Total tension in each td (two cables summed).
• Black td 12, red: td4, green td8
  
• I've removed a mean value using the 60 second before the epicenter time.
• If the telescope was moving (flagged on page 1) then a linear fit to the 60seconds before the epicenter is removed from all the data.
• Middle: magnitude of the fft of the tdkips in each td during the earthquake.
  
• 300 secs starting from the epicenter time is used
• sampling is 1Hz. so any frequencies above .5 Hz will be aliased.
• --> the below tilt sensor plots show the aliasing..
  
• Bottom: magnitude of the fft of the tdkips in each td before quake.
• 300 seconds before the epicenter time is used
• This lets you see what frequencies are present without the earthquake.

A description of the tilt sensor plots:

• The tilt sensors are on the rotatary floor in the dome. They are located close to turret position 75 degrees.
• The pitch sensor measures oscillations along the azimuth arm. It has a range of +/-10 deg
• the roll sensor measures perpendicular to the azimuth arm. I think its range is +/- 2deg
• the sensors are sampled at 5hz.
  
• Page one shows the tilt sensor data during the earthquake.
• top: pitch tilt sensor along the azimuth arm
• bottom: roll tilt sensor perpendicular to azimuth arm.
• For the 2020-01-11 12:54:45 5.9 quake, the pitch sensor had a maximum excursion of +/- 8 degrees.
  
• Page 2:Magnitude spectra of the tilt sensor data
• Black is the pitch sensor, red is the roll sensor.l
  
• top: 300 seconds of data starting at the quake epicenter time
• bottom: 300 seconds before the quake epicenter time.. this shows oscillations not coming from the earthquake.
• Page 3: Show how the 1 sec sampled tiedown kips spectra will alias
• The regular line is the pitch. The line with + is the roll
• top: The spectra is plotted using different colors for every .5 hz bandwidth.
• These are the nyquist zones the will alias when using the 1 sec sampled tiedown data.
• bottom: spectra folded as if it was taken with 1 second sampling.
• Comparing this to the tiedown tension spectra, you can see the where the aliased data is coming from (at least up to 2.5 hz bw).
• eg: for 2020-01-10 22:26:25 tiedown kips spectra
• There is a sharp spike at .45 Hz.. looking at the tilt sensor data.. this spike is probably the 1.55 hz spike
• The tdkips bump at .2 to .3 hz is probably the 1.3 hz spike in the tilt sensor data.
• I'm not sure whether these frequencies are oscillation frequencies of the platform, or frequencies driven by the earthquake itself.
  

Earthquake info.

Useful links to get earthquake info:

•  Ao seismometer via iris network
• https://www.iris.edu/app/station_monitor/#Today/PR-AOPR/webicorder/
• usgs latest earthquakes
• https://earthquake.usgs.gov/earthquakes/map/
• zoom the map to puerto rico
• click the gear icon to get   display options
  

AO seismic station via pr seismic net (2020.. trouble with the plots).

• http://redsismica.uprm.edu/Spanish/
• Use the spanish version, english one doesn't work (fuego popular...)
• click on Monitoreo do estaciones
• scroll button on mouse to enlarge map, click on AO location
• or try this link:http://www.prsn.uprm.edu/Spanish/EstacionesV3/station_description.php?STAT=AOPR&INDEX=159&refresh=2
• Plot/device recording  Names:xyz-PR (see seed Manual).
  
• x- This specifies the bandwidth of the recoding device.
• B broad band
• 10<=sampling rate < 80 hz 8
  
• corner period >=10 secs
• H high broad band
• 80<= sampling rate < 250 Hz
• y- Instrument type code
• H - High gain seismometer
• L  - low gain seismometer
• ..
• N  Accelerometer
• z - Orientation code for the instrument
• Z - vertical
• N - north/south
• E - east/west
• BHZ plots
• 10-80 hz sampling
• accelerometer
• vertical motion
• HNZ plots
• 80-250 hz sampling
• accelerometer
• vertical motion
  

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