Seismic noise characterization at Virgo
Transcript of Seismic noise characterization at Virgo
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 1 -
Seismic noise characterization at VirgoIrene Fiori
(Universita’ di Urbino – INFN Firenze)
for the Virgo Collaboration
• Seismic isolation at Virgo• General features of seismic noise• Sources (preliminary)• Seism from soil to dark fringe at Virgo CITF
• Transfer function• E4: unexpected seismic noise sneaked in…
Outline:
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 2 -
Seismic isolation at Virgo
Mirror
∼ 10 -7 f -2 m Hz -1/2Pre-isolator stage
• Actively controlled todamp horizontal SAresonances below 2 Hz
( inertial damping )
8m
• Multiple mechanical pendulum(5 filters + marionetta + mirror)
• Inverted Pendulum stage (IP)Seism
Super Attenuator (SA):
Ultra-low frequency oscillator (30mHz)
Attenuation performance:
• 10^-13 (horizontal) @ 4 Hz
• 10^-9 (vertical) @ 4 Hz
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 3 -
Goal for seismic noise attenuation
“Seismic Wall”
Crossing point
<<Thermal Noise @ 4.1 Hz :
Residual Seismic Noise Upper Limit@ 4.1 Hz :
Measurement of horizontal seismic noise transmission:
4 × 10-18 m Hz-1/2
9 × 10-17 m Hz-1/2
“Residual seismic mirror vibrations below the thermal noise floorstarting from a few Hz”
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 4 -
Seismic noise: general characteristics
Seism amplitudes (m)
• 10-5 @ 0.1 Hz • 10-7 @ 1. Hz• 10-9 @ 10. Hz
10-6
10-5
10-4
10-1
1 10 102
frequency(Hz)
(m/s
2 )/sq
rt(H
z) Acceleration spectral amplitudes (m/s2/√Hz) x-y-z directions
Tri-axial accelerometers(Kinemetrics EpiSensor)
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-1
1 10 102
frequency(Hz)
m/s
qrt(
Hz)
Displacements (m/√Hz)
• [0.2, 200.] Hz• 7.48×10-7 m/s2
• On concrete floor near BS tower
10-7
f2 (m/√Hz)d ≈~
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 5 -
10-6
10-5
10-4
10-1
1 10 102
frequency(Hz)
(m/s2 )/s
qrt(H
z)
10-6
10-5
10-4
10-1
1 10 102
frequency(Hz)
(m/s2 )/s
qrt(H
z)
Daily seismic variationsDAY .vs. NIGHT seism accelerations
NIGHT .vs. WINDY NIGHT
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 6 -
Monitor of seism RMS in frequency bands
0
10
20
30
40
50
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (DAYS) since July 3rd 00:00
micro
ns/s2
+20.
+5.
Wed
.
Thu.
Fri.
Sat.
Sun.
Mon.
Tue.
Wed
.
Thu.
Fri.
Sat.
Sun.
Mon.
Tue.
3 frequency bands: 0.2-1.Hz ; 1.-4.Hz ; 4.-10.Hz
• 1.0-4.0 Hz: day-night-weekend variations !bridges oscillations excited by heavy trucks ?
• 0.2-1.0 Hz: slow motion ! correlated with wind & waves activity ?
• 4.0-10. Hz: spikes between 10AM-6PM ! human activities on-site
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 7 -
0
10
20
30
40
50
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (DAYS) since July 3rd 00:00
Arb
itrar
y U
nits
RMS seism in [0.7, 0.9] Hz frequency bandWind speed (data from weather station in Pisa)
Observed correlation with wind speed
RMS seism in [0.7, 0.9] HzWind speed
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 8 -
On-line RMS monitor
Earthquakes detection !!
• Nov. 2, Mgn. 4.2, 270 km
• Nov. 1, Mgn. 5.8, 540 km
• Oct.31, Mgn. 5.9, 540 km
• 1 week data at 10 minutes steps
• Work in progress to improve earthquake sensitivity
• Preliminary test version continuously runninghttp://wwwcascina.virgo.infn.it/commissioning/Monitoring_50Hz
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 9 -
Sources: ocean microseism
3
SEISMIC ARRAY ANALISYS
5 tri-axial seismometers(Lennartz 3D/5 sec)
24h of data[0.2, 25.] Hz
• Coherent spectral features at 0.3-0.4 and 0.8 Hz
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 10 -
≈ East !West
speed 750-800 m/s
Plane wave-frontpeak frequency ~ 0.3 Hz
Cross correlation analysis
• Consistent with oceanic microseism:• peak freq. is double the sea wave freq. [R.A.Haubric et al.]• peak freq. position related to weather conditions [T.Braun et al.]
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 11 -
Sources: local traffic1-4 Hz frequency band:
Signal filtered between 1. and 4. Hz
•“Bumps” approx. 30 sec long
• One per min. during daytime
• Minimum at 2AM (local)
• Very reduced during week end
Hypothesis:TRUCKS crossing nearby bridges
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 12 -
Measured ground vibrations under Fi-Pi-Li expressway
Bridge oscillations
(~ 1 km from Virgo site)• Resonant frequencies:
2, 6, 11, … Hz
• Work in progress:coincidence measurement
• Hypothesis:only lowest frequency survive at s = 1 km distance
• General feature of bridges
• Impulses approx. 30 sec long
assuming: Q = 5, v =1000 m/sA(2.Hz)/A(6.Hz) = 0.1
A(s,ω) = A0 exp(- )ω s2vQ
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 13 -
From soil to dark fringe (I)
• Seism contributes to DF noise only below 1.5 Hz, • contribution is mainly from vertical vibrations
10−2 10−1 100 101
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
frequency (Hz)
Coherence of dark fringe signal with seism (E3 e-run)
VERTICALNSEW
0.01 0.1 1. 10 0 0.5 1. 1.5 2. 2.5
seismometeris blind here!
ZOOM: f < 2.5 Hz
Frequency (Hz)Frequency (Hz)
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 14 -
From soil to dark fringe (II)Transfer Function (E3)
VERTNSEW
SA resonances
• Decreasing phase indicates a finite travel time
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 15 -
From soil to dark fringe (III)
• Travel time: of the order of few seconds (~3s) • Ringing lasts for up to 200 seconds (!!)
0 100 200 300 400 500 600 700 800 900−40
−20
0
20
40Vo
lts
0 50 100 150 200 250−40
−20
0
20
40
Volts
0 5 10 15 20 25 30 35 40−40
−20
0
20
40
Volts
time (s)
DF response to impulsive seismic noise (inverse of TF)
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 16 -
• Seismic noise is responsible of the DF noise from 0.4 to 1.6 Hz (!ocean microseism)
• Vertical noise dominates: vertical Inertial damping not implemented (yet)
Seismic noise contribution to Dark Fringe
WESNVerticalTOTALDark Fringe
2
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 17 -
E4 seismic investigation• Same coherence analysis repeated with E4 data
showed many unexpected coherent lines above 10Hz !!Seism .vs. E4 Dark Fringe COHERENCE
Frequency (Hz)1001010.2 200
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 18 -
Frequency (Hz)
CoherenceDF.vs.seism
Dark fringe
Soil accelerations
11.4 13.3 18.6 23.524.6
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 19 -
Sources ?
• Same lines also seen by acoustic channels
• Identified as vibrations of motor devices in CITF building:
• air conditioning, • air cleaning, • vacuum pumps …
11.4
13.3
16.5 19.2
19.9
" seism propagates through air
11.4 18.6 23.524.6
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 20 -
Noise enters from Injection System…
• Laser frequency is locked on MC length⇒ Seismic noise is somehow transmitted
to suspended I.S. mirrors and converted into laser frequency noise in the MC cavity
Same seism coherent lines in laser frequency noisefeedback loop
I.S. (laser + 140m MC cavity) first used in E4
CITF Same seism coherent lines in laser beam
from I.S. to CITF
MC
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 21 -
Which path ?
• Injection System control loops:- Local control on suspended mirrors- Automatic alignment of laser beam
• These loops are fed by cameras and photodiodes placed on soil
Solutions• Short term: steeper low pass filtering in I.S. feedback loops• Virgo 3000: laser frequency stabilization using Dark Fringe signal
coherent seismic lines in feedback error signals
• Seism above 10Hz can be re-injected if feedback loops have not null gain at those frequencies
Investigation still in progress…
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 22 -
Conclusions
• Main sources below 10 Hz: - seismic wave field from the sea at 0.3-0.4 Hz- local traffic 1.- 4. Hz (preliminary results)
• Discussed general characteristics of seism at Virgo site• Seism daily variations occur mainly below 10 Hz
• All dark fringe noise below 1.5 Hz is of seismic origin,- mainly due to vertical seism, currently not actively damped at low frequencies
- above 1.5 Hz seism is efficiently damped by SA• Lesson from engineering runs:seism may have other ways to enter the interferometer(feedback loops).
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 23 -
1
10 -10
10 -20
SA Transfer Function
1 10 1000.1Freq (Hz)
10 -13
4
HOR.VERT. x 10^-4
f -2N
Super Attenuator expected performances
0.01
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 25 -
Which path ?
• Injection System control loops:- Local control on suspended mirrors- Automatic alignment of laser beam
• These loops are fed by cameras and photodiodes placed on soil
Solutions• Short term: steeper low pass filtering in I.S. feedback loops• Virgo 3000: laser frequency stabilization using Dark Fringe signal
coherent seismic lines in feedback error signals
• Seism above 10Hz can be re-injected if feedback loops have not null gain at those frequencies
shaking of IS optic bench mirrors back and forth in front of the beamcould produce frequency noise (optic bench is not seismically isolated)
• Doppler EffectInvestigation still in progress…
Irene Fiori – XXXVIIIth Rencontres De Moriond, March 22-29, 2003 - 26 -
Which path ?• Suspensions: (…unlikely)
MC mirrors are suspended by short SA towers• short towers should attenuate seism down two
at least 3 orders of magnitude below observed values(according to design performance: vert. T.F. = 10^-7 @ 10Hz)
Solutions• Short term: steeper low pass filtering in I.S. feedback loops• Virgo 3000: laser frequency stabilization using Dark Fringe signal
• Injection System control loops:- Local control on suspended mirrors- Automatic alignment of laser beam
• These loops are fed by cameras and photodiodes placed on soil • Seism above 10Hz can be re-injected if feedback loops
have not null gain at those frequencies
Investigation still in progress…