SLIDE 1
International Data Centre Page 1
International Data Centre Page 2
Global grid of master events for waveform cross correlation: design - - PowerPoint PPT Presentation
Global grid of master events for waveform cross correlation: design - - PowerPoint PPT Presentation
Global grid of master events for waveform cross correlation: design and testing Kitov, I., D. Bobrov, and M. Rozhkov International Data Centre Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization Provisional
SLIDE 2
SLIDE 3
International Data Centre Page 3
Background
Comprehensive Nuclear-Test-Ban Treaty
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) obligates each State Party not to carry out any nuclear explosions, independently of their size and purpose. The Technical Secretariat (TS) of the Comprehensive Nuclear-Test-Ban Treaty Organization will carry out the verification of the CTBT. The International Data Centre (IDC) is an integral part of the (currently Provisional) TS. It receives, collects, processes, analyses, reports on and archives data from the International Monitoring System (IMS). The IDC is responsible for automatic and interactive processing of the IMS data and for standard IDC products. The IDC is also required by the Treaty to progressively enhance its technical capabilities.
SLIDE 4
International Data Centre 25 October 2010 Page 4
Objectives
To built a global grid of master events for waveform cross correlation To assess the performance of waveform cross correlation as a technique of seismic monitoring using the global grid of master events
SLIDE 5
International Data Centre 25 October 2010 Page 5
Outline
- 1. Motivation
- 2. Global seismic monitoring: IMS
- 3. Global seismicity: IDC view
- 4. Cross correlation at teleseismic distances
- 5. Actual and grand master events
- 6. Machine learning and classification
- 7. Synthetic master events
- 8. Underground nuclear explosions as master events
- 9. Global cross correlation grid. Design
10.Testing. February 12, 2013
SLIDE 6
International Data Centre Page 6
Cross correlation as an IDC technique
Motivation
- Regional studies demonstrate significant improvement in
detection, location, and magnitude estimation.
At least an order of magnitude!
- Many IMS primary stations are arrays enhancing the capability
- f cross correlation analysis
- For arrays, correlation distance depends on phase and its
slowness
- At teleseismic distances, high level of cross correlation is
- bserved for signals from events spaced by 100 km and even
more
- Remote events may have similar signals
- Small events can be considered as point sources
SLIDE 7
International Data Centre Page 7
IMS, seismic network
Green circles – primary arrays Green triangles – primary 3-C stations Small green circles – auxiliary arrays The primary network includes many arrays
SLIDE 8
International Data Centre Page 8
Global seismicity: the IDC view
Waveform cross correlation relies on high quality master events REB events with zero depth: yellow – a neighbor closer than 50 km; red – no neighbor within 50 km
Monitoring is global. How to populate the aseismic area with quality master event?
SLIDE 9
International Data Centre Page 9
Waveform cross correlation
6 s 6 s CC STA LTA SNR=STA/LTA≥3.0
Detection: CC > CCtr SNR_CC > SNRtr
Multichannel waveforms Master template Four frequency bands Adjusted template length Waveform quality check CC for individual channels Averaged CC trace Detection Multichannel CC-detector better sees signals from slave events close to the master
SLIDE 10
International Data Centre Page 10
Actual and grand masters: Sumatera 2012
- 2
2 4 6 86 88 90 92 94 96 lat, deg long, deg Regular grid REB Real masters main shock
- 2
2 4 6 86 88 90 92 94 96 lat, deg long, deg
1181 REB events between April 11 and May 24 , 2012
- 7 IMS array stations
- 16 master events: actual and grand
masters
- 2763 XSEL hypotheses
- 409 (~15%) randomly chosen XSEL
events were reviewed by analysts
- 119 new REB events
SLIDE 11
International Data Centre Page 11
Machine learning: classification
Nsta XSEL Tree Bagger SVM Naive Bayes 1066 1406 848 1 489 487 613 2 382 253 540 3 2080 324 208 452 4 514 347 256 198 5 129 115 113 80 6 31 31 31 24 7 9 9 9 8 Total 2763 826 617 762
ASAR CMAR GERES MKAR SONM WRA ZALV
SLIDE 12
International Data Centre Page 12
Grand masters: Atlantic Ocean
Cross correlation of signals from remote events 931 REB events; 3 array stations with SNR>3
SLIDE 13
International Data Centre Page 13
Grand masters: Atlantic Ocean
Cross correlation coefficient for 931 events in seismic region 32 Events are ordered by latitude: north to south Matrix of cross correlation coefficients (color coded) Signals correlation does not dependent on the distance between events
SLIDE 14
International Data Centre Page 14
Cross correlation: explosion signals
- 100 waveforms
- 25 underground
nuclear explosions
- 6.2 > mb > 4.5
- 2015 m > H > 150 m
- 60 stations
- 16º > ∆ > 100º
Towards seismic monitoring of underground nuclear explosions
SLIDE 15
International Data Centre Page 15
Cross correlation of explosion signals
Synthetic seismograms: ∆ =30º, 45º, 60º, 90º H=0.1, 0.3, 0.6, 1.0, 2.0 km fc= 0.8 Hz to 4.8 Hz
SLIDE 16
International Data Centre Page 16
Cross correlation of explosion signals
Principal Component Analysis 10 best components for real and synthetic waveforms CCs for 100 real waveforms correlated with real PC CCs for 100 real waveforms correlated with synthetic PC Synthetics demonstrate excellent performance when used for waveforms cross correlation
SLIDE 17
International Data Centre Page 17
Global Cross Correlation Grid
Master: Ten primary seismic arrays at P-wave distances (6 to 96 degrees)
SLIDE 18
International Data Centre Page 18
Global Cross Correlation Grid Segment R = 100 km
SLIDE 19
International Data Centre Page 19
Global Cross Correlation Grid Testing, February 12, 2013
REB - 134 events Grid: 25000 nodes Group 1 = WRA, TORD, MKAR, ILAR, GERES, PDAR, CMAR, SONM, AKASG, BRTR, GEYT Group 2 = ASAR, ZALV, YKA, ARCES, TXAR, KSRS Group 3 = USRK, FINES, NVAR, NOA, MJAR Defining parameters: Templates: simplest 1D synthetic waveform for all arrays, theoretical time delays Detections: SNRmin = 0.5; SNR_CCmin=2.5; CCmin = 0.2; FKSTATmin = 2.5; AZRESmax= 20.0º; SLORESmax = 2.0 s/º; Events: dTorigin = 6s; NSTAmin= 3; AZGAPmax= 330º RESULTS: Total arrivals and hypotheses: 22,900,402 arrivals; 107,969 events; After conflict resolution: SNR_CC>2.5 SNR_CC>3.0 SNR_CC>3.5 SNR>2 XSEL 6,141 events 766 122 2351 REB Matched 92 90 77 101 DPRK 2013: time - 02:57:50.799 , d=24.92 km, OTres=0.1s; nsta=9: AKASG, BRTR, CMAR, GERES, GEYT, ILAR, MKAR, SONM, WRA
SLIDE 20
International Data Centre Page 20
Global Cross Correlation Grid
- V0.1: All master templates are synthetics same at all stations, a version of f-k
analysis
- V0.2: Master templates are station/master specific synthetics in 1D velocity
model
- V0.3: Master templates are station/master/source (e.g. explosion) specific
synthetics calculated for 2D velocity structure (e.g. ak135+CRUST 2.0)
- V1.1: Real master templates are used where possible
- V1.2: Grand master events are applied where possible
- V2.0: The set of principal components are optimized where possible as
- btained by the PCA applied to the complete set of actual and historical
data
- V3.0: Synthetic + real master templates based on principal components with
classification algorithms trained on actual data
SLIDE 21
International Data Centre Page 21
Discussion
- IMS array stations make possible automatic processing based on
waveform cross correlation
- Cross correlation is a powerful technique allowing to reduce the
detection threshold and relative location accuracy by an order of magnitude, i.e. to find by 50% to 100% more (smaller) REB events
- Grand master and synthetic master events may reduce the
magnitude threshold of seismic monitoring by 0.4 units of magnitude
- The Global Cross Correaltion Grid is flexible (e.g. master density,