Toward a joint array and polarization processing from IMS 3-component stations data:

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1 Toward a joint array and polarization processing from IM 3-component stations data: eismic wavefield polarization and its spatial coherency Claire LABONNE*12, Olivier ÈBE1 téphane GAFFET23, François CHINDELÉ1 * Now at Departement of eismology, IG, France 1. CEA, DAM, DIF, F Arpajon, France 2. Univ. Nice ophia Antipolis, CNR IRD, OCA, France ciences & Technology LBB, Rustrel, France 29 June 2017

2 IM EIMIC TATION AND ARRAY Array including serveral 3C stations 6(3C) 25(3C) 4(3C) 7(3C) 4(3C) 6(3C) 5(3C) 4(3C) INGLE 3C TATION TANDARD ARRAY: array of vertical stations single 3C station 3C ARRAY Adapted from Gibbons,

3 WAVE CHARACTERITIC (from 1C to 3C) OURCE MEDIUM OF ROAGATION EIMIC WAVEFIELD Wave characteristics: Frequency content RECORDING Time of arrival and 1C station YTEM duration Amplitude IGNAL ropagation array of stations ROCEING olarization 3C station 3C ARRAY ignal processing techniques do not manage to use the full potential of the 3C array which mainly under-used the polarization Complexity to extent 1C to 3C array processing High order optimization problem Require strong assumptions on the polarization model [Wagner, 1996], [Hobiger 2011] Objectives: Better exploitation of the 3-component stations and arrays large potential by focusing on polarization 3

4 DEFINITION OF OLARIZATION ARAMETER By Fourier analysis, the seismic wavefield records can be decomposed into a sum of elliptical motions olarization state is characterized by a shape and an orientation innegar, 2006 AGE 4 4

5 CAE TUDY Gorkha Earthquake econd main shock Normalized Amplitude (An) tockwell 1996 Rayleigh LBB broad-band 3C seismic array

6 VIUALIZATION OF OLARIZATION Normalized Amplitude (An) circular Rayleigh Ellipticity (𝝆) 𝝆<0,5 linear Rayleigh Energy based mask: election of relevant information Orientation of 𝑎 𝒂 article Motion Ellipticity based mask: election of relevant polarization parameter 6

7 VIUALIZATION OF OLARIZATION 1D Earth model 3C station 3D view N Direct ray path with an azimuth of 75 an incidence of 70 BAZ =75 𝑎𝑆𝐻,𝐿𝑜𝑣𝑒 BAZ=75 E W 𝑎𝑆𝑉 D 𝑎𝑃 BAZ inc=70 V H V H Nepal earthquake 7

8 VIUALIZATION OF OLARIZATION Normalized Amplitude (An) circular Ellipticity (𝝆) linear Orientation of 𝑎 𝝆<0,5 𝒂 Orientation of 𝑐 𝝆>0,5 article Motion Rayleigh article Motion 𝒄 8

9 VIUALIZATION OF OLARIZATION Direct ray path with an azimuth of 75 BAZ = 75 3C station V H V H Nepal earthquake 9

10 VIUALIZATION OF OLARIZATION Normalized Amplitude (An) circular Ellipticity (𝝆) 𝝆<0,5 linear Rayleigh 𝒂 article Motion Orientation of 𝑐 𝝆>0,5 Orientation of 𝑎 Rayleigh article Motion 𝒄 10

11 DEFINITION OF COHERENCY ARAMETER lane wave: same polarization pattern Array aperture smaller than 2km 11

12 DEFINITION OF COHERENCY ARAMETER Deviation in polarization shape and orientation 𝚯𝝆 𝚯𝒂 Less than 1 degree! 𝚯𝒄 Observation of spatial polarization coherency through the LBB array 12

13 RECIE ORIENTATION REQUIREMENT tation orientation with Fiber Optic Gyrocompass recision < 1 urface stations orientation with magnetic compass Error > 5 Gallery stations orientation with surveyor Error ± 5 WITHOUT gyrocompass orientation correction WITH gyrocompass orientation correction Not affected by orientation 𝚯𝝆 𝚯𝒂 Less than 1 degree! 𝚯𝒄 affected by orientation Observation of spatial polarization coherency through the LBB array Inverse process of optimization to orientate the stations of an array relativeley to each other13

14 ARRAY AVERAGED OLARIZATION Θ𝑎 < 5 U Θ𝑐 < 5 COHERENCY based mask Θ𝑎 < 5 Θ𝑐 < 5 electing seismic phases according to their coherent polarization parameters! 14

15 ummary: 3C-2D array processing Complexity to extent 1C to 3C : High order optimization problem Require strong assumptions on the polarization model IM seismic network: ingle station polarization analysis: Vectorial parameter system [Labonne et al., E3 2016a&b] time frequency pola representation Energy ellipticity based masks [Labonne et al., art I, GJI, submitted] single 3C station Array polarization analysis Time frequency pola coherency representation Coherency based mask recise orientation orientation requirement [Labonne et al., art II, GJI, submitted] 3C array low frequency events Objectives: Method improvement: take into account time delays between stations ost-doc: Array processing and polarization analysis joint method 3C array high frequency events Full data analysis of standard IM array data: array of vertical stations colocated to a 3C station Master Thesis: Kazakhtsan seismic array use standard array Automatically identify phases CTBTO regroup nt2017 time-frequency cells into families distance function using cell time-frequency closeness and similarity in polarization All 3C data 15