Software implementations for quality control on seismic surveys: application to short scale networksSoftware implementations for quality control on seismic surveys: application to short scale networksJosep VilaJosep VilaInstitut d’Estudis Catalans. Carme, 47, 08001 Barcelona, Spain. e-mail: jvila@iec.cat

ABSTRACTAn exhaustive analysis of the seismic dataset gathered in the Integrated Field Exercise IFE08 is done in order

ABSTRACTADRMADRMAn exhaustive analysis of the seismic dataset gathered in the Integrated Field Exercise IFE08 is done in order

to evaluate its quality and consistency. By means of an application of a set of quality‐control procedures,potential low quality data, changes in the behavior of seismic signals or unexpected malfunctioning are CHN. #n QC #1 DATAFARM

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potential low quality data, changes in the behavior of seismic signals or unexpected malfunctioning aredetected. The method is based on the analysis of the background seismic noise to detect patterns over whichunforeseen contributions or abnormal operation may be observed, thus detecting any anomaly and reducing

DATAFARM

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WEBunforeseen contributions or abnormal operation may be observed, thus detecting any anomaly and reducingpotentially nonsense data. The analysis consists on quality‐control software implementations that may be runoff line simultaneously with any acquisition task. The method operates the continuous waveform data andy y q pthe procedure applies to segments of a definite fixed length. The data analysis is done both in time andfrequency domain, computing outputs related to averaged amplitudes, averaged squared amplitudes and

resultsQC #2

q y , p g p g p , g q pevolution of predominant frequencies of ground motion waveforms for any desired frequency band. Throughall this analysis, new time series are generated, that allow the quantification of the characteristics of the

Warningy , g , q

seismic signals and its evolution. As a complement, an evaluation of minimum level of noise for all spectralcomponents is carried out by means of a continuous comparison of the output spectra of every new segment

Data preparation (yes/no)Verify headers

Data validation (analysis)p y p p p y gof data with respect to the stored results, keeping the minimum values of each component. The methodologyis based on the stability of the very base levels of noise for a given site. This characteristic allows the use of

Verify headersComplements header infoWrite std. volumes

Energy for selected frequency bands / all (*)Max. amplitude and its frequency for each band (*)A lit d f l t d t l t (*)

y y gdifferent parts of the spectrum to get a good indication of changes of the seismograph system (qualitycontrol), variations of the status of a given site (information of the local structure) and the absolute

Structure data ready to req. Amplitudes for selected spectral components (*)Evaluation of the minimum spectra

), g ( )determination of the response of a station (calibration). This let to obtain a pseudo‐spectrum that can beconsidered as the minimum noise in absence of any type of transitory signal, for a given site. Once a

(*) Generation of a new time series (2nd level)

y yp y g greference level is reached, systematic signals above or below the noise pattern levels indicate bad quality ofthe data. This avoids late identification of malfunctioning and a clear estimation of the operation of a full set

The software based system can be rapidly implemented as a stand alone complement may run in parallel to anyg p

of data is obtained. Stable transitory signals, systematic biases or resonances induced by diverse typephenomena are some of the indicators, that reflects permanent site effects and identify potential low quality

The software‐based system can be rapidly implemented as a stand alone complement, may run in parallel to anyother applications and the output data is provided instantaneously. Malfunctioning or permanent resonances aredetected almost at once After an initial adjust to make data from OSI (SAMS) data structure ready to be entered

data or malfunctioning. This prevents the loss of effective data and increases the efficiency of any techniqueof seismic monitoring.

detected almost at once. After an initial adjust to make data from OSI (SAMS) data structure ready to be enteredand the most appropriate frequency bands are chosen, the off line analysis of a time span of data requires fewminutes per station and day of stored data The methodology has provided very good results and it is nowadaysminutes per station and day of stored data. The methodology has provided very good results and it is nowadaysimplemented in several networks in Europe as a quality control monitoring system

PROCEDURE AND METHODOLOGY To obtain the Earth’s fluctuation pattern for a given site we defined a technique to obtain a reference level based on the spectral analysis of fixed length segments. By continuouslycomparing the amplitude of all spectral components and selecting the minimum value for each frequency bin, we construct a "spectrum" that contains only the lowest level for eachfrequency. If the operation is continued for long enough, this method provides a "pseudo spectrum" without any spurious (cultural noise), transitory (earthquakes) or temporary(weather influences) signal inputs. It is that signal that we term the Base Level Noise Seismic Spectrum (BLNSS). Its shape depends on the permanent sources and the medium in whichseismic waves has been propagated and represents the quasi‐stationary status of a given site.

The computation of the BLNSS for a given site reveals high temporal stability, suggesting The BLNSS presents a spatial stability in the frequency band (0.03 – 0.4 Hz) and for The temporal evolution of frequency componentsthat a first estimation of the BLNSS of a given site can be obtained by analyzing one yearof continuous waveform data (left). It is important to note that the BLNSS is a signal

continental stations in the Northern Hemisphere the spectra practically coalesce. Theseobservations raise the question whether an underlying spectral structure exists in the

close to the maximum peak of the BLNSS alsodisplays a high point to point connection between

around 20 dB below the spectra of a an earthquake (right). microseism frequency range which reflects the Earth's response during quiet atmosphericconditions that could be used as a reference for QC’ing a given site .

stations at distances of the order of 1000 km.

BACKGROUND APPLICATION

Virtual European Broadband Seismographic Networkhttp://www.orfeus‐eu.org/

NOA Quality Control Seismic Systemhttp://bbnet.gein.noa.gr

Monitoring the Reawakening of Canary Islands’ Teide Volcanohttp://teide.am.ub.es/

A near real‐time QC procedure is currently applied to the continuous incomingwaveform data of the VEBSN stations, with the aim to detect malfunctioning of

By means of a Bilateral Cooperation between Spain and Greece, a near real‐time QC system was been setup at the Institute of Geodynamics of the

Starting in 2004, the QC system has shown to be very useful for monitoringchanges in the behavior of the volcanic processes. On 5 December 2004 a

the seismic instrumentation, changes of system response information in time,changes in local site conditions and incorrect system response information

National Observatory of Athens to monitor the status of all incomingbroadband seismic stations recorded by the Hellenic Broadband Seismic

fissure with fumarole emission appeared on the NE flank of Teide volcano. Thiswas preceded by a significant increase in low‐frequency seismic energy 9 days

(metadata). Network . The system operates since 2005. earlier, with a return to the normal level a few hours after the fissure aperture.

• Vila J. The Broadband Seismic Station CAD: Site Characteristics and Background Noise. BSSA, 88 (1), 297‐303, 1998.References • Vila J. & Macià R. The Broadband Seismic Station CADI . Part II: Long Period Variations of Background Noise.  BSSA, 92 (8), 3329‐3334, 2002.• Correig,  A.M. et al. 1/fα noise as a source of the Earth's fluctuations. Europhys. Lett., 74 (4), 581‐587, 2006.• García A Vila J et al Setting up a Real Time Quality Control Reawakening EOS Trans Am Geophys Union Vol 87 No 6 61;65 7 Feb 2006

References• García, A., Vila, J. et al.  Setting up a Real Time Quality Control… Reawakening. EOS, Trans. Am. Geophys. Union, Vol. 87, No. 6, 61;65, 7 Feb. 2006.• Vila, J.,et al.  Analysis of the Unrest of Active Volcanoes by means of Variations of the BLNSS.  J. Volcanol. Geotherm. Res., V. 153, 11‐20, 2006• Correig, A.M. et al. Microseism Activity and Earth's Equilibrium Fluctuations. In: Nonlinear Dynamics in Geosciences, Chapter 5, 69‐85, 2007.• Vila, J. et al. NRT analysis of seismic data of active volcanoes: Software implementations of time sequence data analysis. NHESS, 8, 1–6, 2008. • Vila, J. et al. On the stability of the Earth’s fluctuations spectral peaks at their lowest amplitude level. Fluctuations and Noise Letters, in press, 2009. 

Software implementations for quality control on seismic surveys: application to short scale networksSoftware implementations for quality control on seismic surveys: application to short scale networksJosep VilaJosep VilaInstitut d’Estudis Catalans. Carme, 47, 08001 Barcelona, Spain. e-mail: jvila@iec.cat

APPLICATION Th SAMS N k d l d i h IFE08APPLICATION: The SAMS Network deployed in the IFE08

DATADATADuring the IFE08 a total of 32 seismic stations were deployed. 27 of them were mini‐arrays and 5 were 3‐component. The recording period covers from September 4 to September 29 and the amount of data gatheredfor each station depends on the daily operations. Stations consisted in Reftek‐130 digitizers recording data fromsensors Lennartz Le3D / Le1D(V.) All channels were configured to record data in continuous mode at a samplingrate of 500 sps thus meaning a total amount of raw data of the order of 0.5 TB.

To obtain a first approach of the suitability of the QC procedures in the present works data was decimated to 25sps and the length of the segments was set of 10 minutes. The QC subroutines have been applied to 17 miniarrays and 2 three component stations.

Mini array configuration thatMini array configuration thatoperated in the IFE08.

Digitizer (left) and sensor (middle)Digitizer (left) and sensor (middle)deployed in the IFE08 SAMS Network.Right: Process of data screeningRight: Process of data screeningperformed at the SAMS lab.

Map and distribution of the seismic stations/arrays over the 1000 km2 of the Inspection Area

Photographs of the process of physical check, installation, maintenance and data screening in the SAMS lab

DATA ANALYSIS RESULTS (base level noise BLN)DATA ANALYSIS RESULTS (base level noise BLN)

BLN of the Z components of the 3C stations analyzed in Zoom of the BLN in the frequency band 1 Hz ‐ 10 Hz. The BLN of all channels of station AC04 (left) and AC07 (right). BLN of all channels of station AC11 (left) and AC17 (right).this work. The right plot excludes stations presentingsome wide band differences. Note the similar levels of the

right plot displays a comparison of the BLN for stationspresenting clear differences with respect to the common

AC04N/E/W only reflects instrumental noise (no sensorconnected) and AC07C displays different noise levels for

The horizontal components of AC11C could be affected bysome tilting effect. E‐W component of AC17 clearly

and the existence of the physical frequency of the sensor. shape. Note the presence of the physical frequency. the horizontal components. displays some different behaviour.

CONCLUSIONSDATA ANALYSIS RESULTS (temporal evolution of spectral parameters) CONCLUSIONS• The QC procedures based on the analysis of background seismic

i h b d d b i bl b li dnoise has been demonstrated to be suitable to be applied tocontrol the performance of SAMS surveys in OSI activities.

• The application to the data gathered in the Integrated fieldpp g gExperiment 08 (IFE08) does not present any indication of criticalmalfunction nor low quality of the implementation of the survey.malfunction nor low quality of the implementation of the survey.

• Several imperfections seems to arise when analyzing the very• Several imperfections seems to arise when analyzing the verybase levels of noise for some stations. However, these look likei t i i lf ti l t d t li it ti f th i t t ti

Time evolution of the integrated spectral square amplitude of the Zt f th 3C t ti l d i thi k i th f b d

Left: Time evolution of the integrated spectral square amplitude of stationAC05C i 5 f b d Ri ht C i f ti l ti f th intrinsic malfunction related to limitations of the instrumentation

and are not related to the setup processes and procedures.components of the 3C stations analyzed in this work in the frequency band1‐4 Hz (left) and 3‐6 Hz (right). Note the general similarities as well as thediscrepancies that displa s the ello trace (AC28)

AC05C in 5 frequency bands. Right: Comparison of time evolution of theintegrated spectral square amplitude of 8 stations (*C.SHZ). Note the

t di i f t ti AC28 d AC03

• The implementation of a parallel automatic software baseddiscrepancies that displays the yellow trace (AC28). apparent discrepancies of stations AC28 and AC03.

methodology would result in a considerable advance in preventinglow quality data in an OSI‐type survey.q y yp y

•The detection and pattern recognition of a given site over whichThe detection and pattern recognition of a given site over whichunforeseen contributions or abnormal operation may be observedis suitable to identify anomalies and reduce low quality datais suitable to identify anomalies and reduce low quality data.

h i ifi i f i h ibili l h• From the scientific point of view, the possibility to apply the QCsubroutines to a short scale network has provided new approachesto the knowledge of the coherency of high frequency spectralcomponents of the microseismic noise wavelength.p g

• A more detailed study of the full set of data is expected toA more detailed study of the full set of data is expected toprovide new insights on the performance of OSI‐SAMS survey inrevealing particular aspects with the aim to improve the efficiencyTime evolution of the maximum amplitude and its corresponding frequency in two frequency bands These plots Time evolution of spectral components The scale revealing particular aspects with the aim to improve the efficiencyin data analysis procedures.

Time evolution of the maximum amplitude and its corresponding frequency in two frequency bands. These plotsallow to notice the presence of monochromatic resonances or spurious frequency components . Note thealready mentioned discrepancies shown by station AC28 (yellow dots)

Time evolution of spectral components. The scaleof the network provides spectral components becoherent up to 6 Hz Note also the discrepanciesalready mentioned discrepancies shown by station AC28 (yellow dots). coherent up to 6 Hz. Note also the discrepanciesof AC28 (yellow dots).

AcknowledgementsThe author wishes to express his gratitude to the Observatories and Research Facilities for European Seismology (ORFEUS) for their assistance on

AcknowledgementsThe author wishes to express his gratitude to the Observatories and Research Facilities for European Seismology (ORFEUS) for their assistance on software applications. Reinoud Sleeman, Ramon Macià, Ramon Ortiz and Antoni M. Correig are thanked for their assistance in many aspects of the development of the quality control procedures.This scientific study has been  supported by the Spanish Government as a part of a voluntary contribution to the Provisional Technical Secretariat of the CTBTO Preparatory Commission.