Comparative Analysis of Earthquake Data Recorded by Hydrostatic Level System and Precision Laser Inclinometer

1. Comparative analysis of earthquake datarecorded by the Hydrostatic Level System andthe Precision Laser Inclinometer instruments N. Azaryan1, V. Batusov1, J. Budagov1, V. Glagolev1, M. Lyablin1, G. Trubnikov1, G. Shirkov1, J.-Ch. Gayde2, B. Di Girolamo2, A. Herty2, H. Mainaud Durand2, ‎D. Mergelkuhl2, V. Rude21-JINR Joint Institute for Nuclear Research2-CERN European Organization for Nuclear Research Presented by M. Lyablin CLIC workshop 2016 CERN Geneva

2. The Task formulation • During the previous  CLIC workshop 2015 when discussing the first Precision Laser Inclinometer (PLI) data a common proposal to compare the PLI results with some other angular seismograph measurements was expressed. • This comparative analyses between the PLI and the HLS (Hydrostatic Level System) has been made using data recorded after the 7.8 Mag Nepal Earthquake of 25 April, 2015.

3. Equal atmospheric pressure in the system (only one point open to air) Network pipe d2 Аir d1 Δx θ B А Water Earth surface Interconnected vessels L Hydrostatic Level System • HLSis made of two water level sensors separated by the distance L and connected by the Network Pipe • A specific feature of the HLS is equality of the atmospheric pressure over the water surface. • When the basement inclines the level of water in the sensors is changed and these sensors data allow one to calculate the ground surface tilt angle θ.

4. The 37m long HLS positioned in the ATLAS detector experimental Hall The Earth surface angular motion recorded by the 37 m HLS • The own oscillation period is 300 seconds which corresponds to the limitation of the registration of high-frequency oscillations by 3.3 10-3Hz. • The sensitivity to the Earth surface angular inclination in the working frequencies interval [10-6 ; 3.3 10-3] Hz was equal to [5 10-9; 3 10-11 ] rad/Hz1/2.

5. The 150m long HLS positioned in the Transfer Tunnel #1 The Earth surface angular motion registered by the 150 m HLS • The own oscillation period is 13.3 minutswhich corresponds to the limitation of the registration of high-frequency oscillations by 1.1 10-3Hz. • The sensitivity to the angular inclination of the Earth surface in the working frequencies interval [3 10-7; 1.1 10-3] Hz was equal to [10-9; 3 10-11] rad/Hz1/2.

6. before inclination after inclination QPr after before Laser before Laser beam Laser spot 2θ after θ Cuvette with liquid Horizontal surface of the liquid (reference level) Support S The Precision Laser Inclinometer • The PLI uses the inclination of the laser ray reflected from liquid surface when the basement tilt takes place . • Essential that the reflected angle is twice larger than the basement tilt angle θ.

7. The calibration of the PLI • By the micrometric screw the PLI basement was inclined on 15.6 μrad. • Having made 22 inclinations one determined the calibration coefficient K connecting the basement tilt angle in μradand the quadrant photosensor signal in V. It was found that K=520±50 μrad /V.

8. The Microseismic oscillations recorded with the PLI The daily record of the microseismic angular activity of the Earth surface The main PLI recorded signal is due to the microseismic angular oscillations also called the “Microseismic Peaks”. The long term variations of angular slope are connected with the noise : the angular jitter in laser ray irradiation.

9. The Fourier analyses of the PLI registered microseismic oscillations • The PLI frequency interval is [10-3 ; 1] Hz. • The PLI sensitivity is found to be [10-9; 10-10] rad/Hz1/2.

10. The registration of the NEPAL 25 April, 2015 Earthquake 7.8 Mag by the 37m long and 150m long HLS’s • The strong (>7.5 Mag) Earthquakes are usually last for more than 1 hour and their low frequency components fall into the HLS registration interval. • Taking the Nepal Earthquake data obtained by the PLI and both HLS we make the comparison of all available experimental observation results.

11. The registration of the NEPAL 25 April, 2015 Earthquake by the PLI • Practically all components of the Nepal Earthquake are within the sensitivity of the PLI registration frequency interval. • One can distinguish three time intervals A, B, and C in the Earthquake registered.

12. The registration of the NEPAL 25 April, 2015 Earthquake by the PLI(Intervals A and B) The A- Interval: The high frequency earth surface angular oscillations with the period of 1-3 sec and amplitude by 5 μrad. The B- Interval: The medium-frequency earth surface angular oscillations with period of 3-10 sec and amplitude by 5 μrad.

13. The registration of the NEPAL 25 April, 2015 Earthquake by the PLI (Intervals C) The C- Interval: The low frequency earth surface angular oscillations with the period of 10-25 sec and amplitude by 4 μrad. The Fourier analyses of the earthquake (A+B+Cintervals) An intense oscillation are being observed in the [0.o4 ; 0.08] Hz frequency interval.

14. The comparison of the PLI averaged data with 37m HLS data The PLI registered Nepal Earthquake data (moving average of period “60”) The registration of the NEPAL Earthquake by the 37 mlong HLS

15. The comparison of the PLI averaged data with 150m HLS data The PLI registered Nepal Earthquake data (moving average of period “300”). The registration of the NEPAL Earthquake by 150 mlong HLS.

16. The Proposal on the creation of the “HLS +PLI” measurement complex • Joint measurement complex with the HLSes and PLI instruments allow for precise detection of any seismic activity induced angular oscillation in the[310-7 ; 1] Hz interval with better than 10-9rad/Hz1/2sensitivity . • The high precision PLI instrument would additionally contribute to the fine adjustment and calibration of the research equipment. If used together the survey devices (PLI + HLSes) are of high importance for the precise positioning of accelerator elements like the low-b triplets for increasing collider luminosities available for experiments in the frame of projects such as the High Luminosity-LHC (HL-LHC).

17. Conclusion • The main characteristics of two Hydrostatic Level Systems 37 m long, located in the ATLAS Experimental Hall, and 150 m long, located in the CERN Transfer Tunnel 1, for the first time were determined experimentally. • The HLS own frequencies of the oscillation limit the registration of the Earth surface angular oscillations in the high frequency band as follows: • HLS (37) own frequency of0.0033 Hz (300 sec period) • HLS (150) own frequency of 0.0011 Hz (800 sec period) • The HLS sensitivities in [310-7; 10-3] Hz range are: • HLS (37) sensitivity 5 10-9 rad • HLS (150) sensitivity 10-9 rad • For the Precision Laser Inclinometer the basic limitation in the low frequency band is caused by the laser beam angular oscillations (jitter) due to noise. That limits the sensitivity to about 10-6 rad in the [10-6; 10-5] Hz interval. • The PLI and the two HLSes data have been compared in the [10-4 ; 10-3] Hz interval for the recording of the Nepal ,April 25, 2015 earthquake. • The compatibility of the two data sets has been demonstrated for both the earthquake time characteristics and its amplitude shape. That demonstrates the PLI suitability for the recording of seismic origin events. • It is proposed to have a joint (HLSes + PLI) detector setup to reach a higher precision (better than 10-9 rad) for recording micro-seismic Earth surface angular activities in a wide frequency band between 3 10-7 Hz (one month period) and 1 Hz.