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Sample records for broadband seismic stations

  1. New Seismic Noise Models Obtained Using Very Broadband Stations

    NASA Astrophysics Data System (ADS)

    Abd el-aal, Abd el-aziz Khairy; Soliman, Mahmoud Sami

    2013-11-01

    It has been two decades since the last comprehensive standard model of ambient earth noise was published Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93-322, 1993). The PETERSON model was updated by analyzing the absolute quietest conditions for stations within the GSN ( Berger et al. in J Geophys Res 109, 2005; Mcnamara and Buland in Bull Seism Soc Am 94:1517-1527, 2004; Ringler et al. in Seismol Res Lett 81(4) doi:10.1785/gssrl.81.4.605, 2010). Unfortunately, both the original model and the updated models did not include any deployed station in North Africa and Middle East, which reflects the noise levels within the desert environment of those regions. In this study, a survey was conducted to create a new seismic noise model from very broadband stations which recently deployed in North Africa. For this purpose, 1 year of continuous recording of seismic noise data of the Egyptian National Seismic Network (ENSN) was analyzed in order to create a new noise model. Seasonal and diurnal variations in noise spectra were recorded at each station. Moreover, we constructed a new noise model for each individual station. Finally, we obtained a new cumulative noise model for all the stations. We compared the new high-noise model (EHNM) and new low-noise model (ELNM) with both the high-noise model (NHNM) and low-noise model (NLNM) of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93-322, 1993). The obtained noise levels are considerably lower than low-noise model of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93-322, 1993) at ultra long period band (ULP band), but they are still below the high-noise model of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93-322, 1993). The results of this study could be considered as a first step to create

  2. Swiss-AlpArray temporary broadband seismic stations deployment and noise characterization

    NASA Astrophysics Data System (ADS)

    Molinari, Irene; Clinton, John; Kissling, Edi; Hetényi, György; Giardini, Domenico; Stipčević, Josip; Dasović, Iva; Herak, Marijan; Šipka, Vesna; Wéber, Zoltán; Gráczer, Zoltán; Solarino, Stefano; Swiss-AlpArray Field Team; AlpArray Working Group

    2016-10-01

    AlpArray is a large collaborative seismological project in Europe that includes more than 50 research institutes and seismological observatories. At the heart of the project is the collection of top-quality seismological data from a dense network of broadband temporary seismic stations, in compliment to the existing permanent networks, that ensures a homogeneous station coverage of the greater Alpine region. This Alp Array Seismic Network (AASN) began operation in January 2016 and will have a duration of at least 2 years. In this work we report the Swiss contribution to the AASN, we concentrate on the site selection process, our methods for stations installation, data quality and data management. We deployed 27 temporary broadband stations equipped with STS-2 and Trillium Compact 120 s sensors. The deployment and maintenance of the temporary stations across 5 countries is managed by ETH Zurich and it is the result of a fruitful collaboration between five institutes in Europe.

  3. Broadband Seismic Station Deployment at Hadabat Al-Marhi, Halban, Saudi Arabia

    SciTech Connect

    Rodgers, A; Lewis, J P; Al-Amri, A

    2002-02-11

    A broadband three-component seismic station was deployed on the Arabian Shield near the town of Halban in central Saudi Arabia. This site is near the proposed site of a primary seismic array (PS38) of the International Monitoring System (IMS) of the Comprehensive Nuclear Test-Ban Treaty (CTBT). The purpose of this deployment was to collect calibration data for the primary array to be deployed in the future.

  4. Significant technical advances in broadband seismic stations in the Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Anglade, A.; Lemarchand, A.; Saurel, J.-M.; Clouard, V.; Bouin, M.-P.; De Chabalier, J.-B.; Tait, S.; Brunet, C.; Nercessian, A.; Beauducel, F.; Robertson, R.; Lynch, L.; Higgins, M.; Latchman, J.

    2015-04-01

    In the last few years, French West Indies observatories from the Institut de Physique du Globe de Paris (IPGP), in collaboration with The UWI Seismic Research Centre (SRC, University of West Indies), have modernized the Lesser Antilles Arc seismic and deformation monitoring network. 15 new, permanent stations have been installed that strengthen and expand its detection capabilities. The global network of the IPGP-SRC consortium is now composed of 20 modernized stations, all equipped with broadband seismometers, strong motion sensors, Global Positioning System (GPS) sensors and satellite communication for real-time data transfer. To enhance the sensitivity and reduce ambient noise, special efforts were made to improve the design of the seismic vault and the original Stuttgart shielding of the broadband seismometers (240 and 120s corner period). Tests were conducted for several months, involving different types of countermeasures, to achieve the highest performance level of the seismometers. GPS data, realtime and validated seismic data (only broadband) are now available from the IPGP data centre (http://centrededonnees.ipgp.fr/index.php?&lang=EN). This upgraded network feeds the Caribbean Tsunami Warning System supported by UNESCO and establishes a monitoring tool that produces high quality data for studying subduction and volcanic processes in the Lesser Antilles arc.

  5. Weather-related Ground Motions Recorded by Taiwan Broadband Seismic Network Stations

    NASA Astrophysics Data System (ADS)

    Yang, C. F.; Chi, W. C.; Lai, Y. J.

    2015-12-01

    Broadband seismometers record ground motions, which can be induced by weather-related processes. Analyzing such signals might help to better understand those natural processes. Here, we used continuous seismic data, meteorological data and stream data to analyze the weather-related ground motions during typhoon cases and rainy season case in Taiwan. We detected some long period seismic signals at the station Mahsi (MASB) during three meteorological cases (Typhoon Kalmaegi in 2008, Typhoon Morakot in 2009 and the East Asian rainy season in 2012). The amplitude of the seismic waveform correlated with the amount of the precipitation and the derivative of water level and discharge in the nearby river. According to the relationships of waveforms in main and minor rainfall events, we derived apparent source time functions (ASTFs) and used the ASTFs to estimate and quantify the precipitation of main rainfall events in the cases. The estimated precipitation has high correlation coefficients (> 0.82) with the observation. It shows that the long period seismic data may be applied to rainfall monitoring.

  6. A deployment of broadband seismic stations in two deep gold mines, South Africa

    USGS Publications Warehouse

    McGarr, Arthur F.; Boettcher, Margaret S.; Fletcher, Jon Peter B.; Johnston, Malcolm J.; Durrheim, R.; Spottiswoode, S.; Milev, A.

    2009-01-01

    In-mine seismic networks throughout the TauTona and Mponeng gold mines provide precise locations and seismic source parameters of earthquakes. They also support small-scale experimental projects, including NELSAM (Natural Earthquake Laboratory in South African Mines), which is intended to record, at close hand, seismic rupture of a geologic fault that traverses the project region near the deepest part of TauTona. To resolve some questions regarding the in-mine and NELSAM networks, we deployed four portable broadband seismic stations at deep sites within TauTona and Mponeng for one week during September 2007 and recorded ground acceleration. Moderately large earthquakes within our temporary network were recorded with sufficiently high signal-to-noise that we were able to integrate the acceleration to ground velocity and displacement, from which moment tensors could be determined. We resolved the questions concerning the NELSAM and in-mine networks by using these moment tensors to calculate synthetic seismograms at various network recording sites for comparison with the ground motion recorded at the same locations. We also used the peak velocity of the S wave pulse, corrected for attenuation with distance, to estimate the maximum slip within the rupture zone of an earthquake. We then combined the maximum slip and seismic moment with results from laboratory friction experiments to estimate maximum slip rates within the same high-slip patches of the rupture zone. For the four largest earthquakes recorded within our network, all with magnitudes near 2, these inferred maximum slips range from 4 to 27 mm and the corresponding maximum slip rates range from 1 to 6 m/s. These results, in conjunction with information from previous ground motion studies, indicate that underground support should be capable of withstanding peak ground velocities of at least 5 m/s.

  7. Five Years of Data at the Monterey Ocean Bottom Broadband Seismic Station (MOBB)

    NASA Astrophysics Data System (ADS)

    Dolenc, D.; Romanowicz, B.; McGill, P.; Neuhauser, D.; Uhrhammer, R.

    2007-12-01

    We present an overview of the results obtained at MOBB in the past 5.5 years of its continuous operation. In particular we focus on the observations of the long-period ocean surface gravity waves (infragravity waves; 0.002 to 0.05 Hz) and different methods to remove the long-period background and signal-generated noise from the seismic observations. MOBB was installed 40 km offshore in the Monterey Bay at a water depth of 1000 m in April 2002 in collaboration between Berkeley Seismological Laboratory and Monterey Bay Aquarium Research Institute (MBARI). It is located west of the San Gregorio Fault and represents the first step towards extending the onshore broadband seismic network in northern California westward of the Pacific-North America plate boundary. MOBB comprises a three- component broadband seismometer Guralp CMG-1T, sensitive over a wide frequency range, from 50 Hz to 2.8 mHz (360 s), a water current meter measuring current speed and direction, and a differential pressure gauge. At present, the station is autonomous and the data are on average retrieved every 4 months using MBARI's remotely operated vehicle Ventana. Work is under way to connect it to the MARS (Monterey Accelerated Research System) cable so that it will contribute continuous real time data to the northern California earthquake monitoring system. Lessons learned from the MOBB deployment as well as noise removal techniques that are specific to the ocean bottom installation will provide us reference for future installations of broadband seismic stations in the oceans. When compared to the quiet land stations, ocean bottom seismic station MOBB shows increased background noise in the band pass of interest for the study of regional and teleseismic signals. This is mainly due to deformation of the seafloor under the pressure forcing by infragravity waves. Also observed is additional signal- generated noise which is due to the reverberations in the shallow sedimentary layers as well as in the

  8. Analysis of broadband seismic noise at the German Regional Seismic Network and search for improved alternative station sites

    NASA Astrophysics Data System (ADS)

    Bormann, P.; Wylegalla, K.; Klinge, K.

    The German Regional Seismic Network (GRSN) comprizes now 16 digital broadband stations equipped with Wieland-Streckeisen STS-2 seismometers, 24-bit dataloggers and a seismological data center at Erlangen. It covers the whole territory of Germany with station-spacings between 80 km to 240 km. The stations are sited in very different environments ranging from near shore at the Baltic Sea coast up to distances of about 700 km from the coast, both within cities and up to about 10 km away from any major settlement, industry or traffic roads. The underground varies from outcropping hard rocks in Hercynian mountain areas, sedimentary rocks in areas of Mesozoic platform cover to up to 1.5 km unconsolidated Quarternary and Tertiary subsoil. Accordingly, seismic background noise varies in a wide range between the upper and lower bounds of the new global noise model. The noise conditions at the GRSN have been investigated systematically by means of displacement power spectral analysis within the frequency range 10-2 5 for RUE and > 10 for BSEG have been confirmed for frequencies between about 0.6 Hz 3 Hz. Strong lateral velocity and impedance contrasts between the outcropping Triassic/Permian sedimentary rocks and the surrounding unconsolidated Quarternary/Tertiary sediments are shown to be the main cause for the strong noise reduction and signal-to-noise ratio improvement at RUE and can account for about 50% of the noise reduction at BSEG.

  9. Investigation of seismic anisotropy beneath the Dead Sea fault using dense networks of broadband stations

    NASA Astrophysics Data System (ADS)

    Kaviani, Ayoub; Hofstetter, Rami; Rümpker, Georg; Weber, Michael

    2013-07-01

    waveforms from core-refracted (SKS) phases recorded at 105 portable stations belonging to the DESERT and DESIRE campaigns and nine permanent broadband stations of the Israel Seismological Network are analyzed to study polarization seismic anisotropy beneath the region of the Dead Sea Transform fault in the Middle East. Shear wave splitting parameters exhibit variations with back azimuth (initial polarization) of the incoming SKS waves. The pattern of this variation is nearly constant along the strike of the fault suggesting a laterally uniform anisotropic structure beneath the Dead Sea region. The modeling of the azimuthal variations of the shear wave splitting parameters and split waveforms yields two-layered anisotropic models consisting of an upper layer with nearly N-S symmetry axis and a deeper layer with around N25°E symmetry axis. The split time is almost equally partitioned between the upper and lower layers allotting a value of 0.6-0.8 s to each layer. 2-D finite difference modeling across the southern segment of the Dead Sea Transform fault demonstrates that anisotropic structure in the strike-normal direction is relatively uniform. The Dead Sea Transform fault appears not to have a significant role in the development of the regional anisotropic fabric. The upper anisotropic layer is possibly related to a fossil fabric in the lithosphere, inherited from the Precambrian Pan-African Orogeny. The lower layer may be related to the mantle deformation due to the relative motion between the lithospheric plates and the asthenosphere and possibly affected by the local flow field due to mantle plumes as inferred by other studies.

  10. The GEOSCOPE broadband seismic observatory

    NASA Astrophysics Data System (ADS)

    Douet, Vincent; Vallée, Martin; Zigone, Dimitri; Bonaimé, Sébastien; Stutzmann, Eléonore; Maggi, Alessia; Pardo, Constanza; Bernard, Armelle; Leroy, Nicolas; Pesqueira, Frédéric; Lévêque, Jean-Jacques; Thoré, Jean-Yves; Bes de Berc, Maxime; Sayadi, Jihane

    2016-04-01

    The GEOSCOPE observatory has provided continuous broadband data to the scientific community for the past 34 years. The 31 operational GEOSCOPE stations are installed in 17 countries, across all continents and on islands throughout the oceans. They are equipped with three component very broadband seismometers (STS1, T240 or STS2) and 24 or 26 bit digitizers (Q330HR). Seismometers are installed with warpless base plates, which decrease long period noise on horizontal components by up to 15dB. All stations send data in real time to the IPGP data center, which transmits them automatically to other data centers (FDSN/IRIS-DMC and RESIF) and tsunami warning centers. In 2016, three stations are expected to be installed or re-installed: in Western China (WUS station), in Saint Pierre and Miquelon Island (off the East coast of Canada) and in Walis and Futuna (SouthWest Pacific Ocean). The waveform data are technically validated by IPGP (25 stations) or EOST (6 stations) in order to check their continuity and integrity. Scientific data validation is also performed by analyzing seismic noise level of the continuous data and by comparing real and synthetic earthquake waveforms (body waves). After these validations, data are archived by the IPGP data center in Paris. They are made available to the international scientific community through different interfaces (see details on http://geoscope.ipgp.fr). Data are duplicated at the FDSN/IRIS-DMC data center and a similar duplication at the French national data center RESIF will be operational in 2016. The GEOSCOPE broadband seismic observatory also provides near-real time information on global moderate-to-large seismicity (above magnitude 5.5-6) through the automated application of the SCARDEC method (Vallée et al., 2011). By using global data from the FDSN - in particular from GEOSCOPE and IRIS/USGS stations -, earthquake source parameters (depth, moment magnitude, focal mechanism, source time function) are determined about 45

  11. Data quality control of ADSN Broadband stations

    NASA Astrophysics Data System (ADS)

    Alili, Azouaou; Yelles-chaouche, Abd el karim; Allili, Toufik; Messemen, Walid

    2014-05-01

    In this work we present the analysis of continuous waveform of the Algerian digital seismic network recorded during five years from 2008 to 2013 for twenty broadband stations using the power spectral densities (PSDs) and their corresponding probability density functions (PDFs) algorithm of McNamara, and Buland (2004). ADSN Broadband stations data quality is one main concern and interest of ADSN technical team. Indeed, the quality of the data from broadband stations is continuously controlled in quasi-realtime using "PQLX" (Pascal Quick Look eXtended) software to compute the PDFs and PSDs during the operation of the stations at different frequency range. At each station the level of noise is shown, which we can see diurnal and seasonal variation. From the data analysis, most of the ADSN Broadband stations display good records in the several frequency domains in relation with their site installation. However some of stations near the urban areas could present some noisy disturbances. This led sometimes to generate some ghost events. In the low frequency, some stations could be still influenced by the temperature variations. This long period of records from 2008 to 2013, led us to analyze and control the several stations year by year taking into account the seasons and to know about their work during five years. This analysis is also very important to improve in the future quality of station installation and choose the optimal station design in aim to reduce cultural noise and large fluctuation of temperature and pressure. Key words: PQLX, PDFs, PSDs, Broad Band

  12. The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

    NASA Astrophysics Data System (ADS)

    Fontaine, Fabrice R.; Roult, Geneviève; Michon, Laurent; Barruol, Guilhem; Muro, Andrea Di

    2014-04-01

    Seismic records from La Réunion Island very broadband Geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the Piton de la Fournaise volcano. Tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation-deflation cycle. Tilt trend indicates that the small-volume summit eruption of 18 February occurred during a phase of continuous inflation that started in January 2007. Inflation decelerated 24 days before a second short-lived, small-volume eruption on 30 March, almost simultaneous with a sudden, large-scale deflation of the volcano. Deflation rate, which had stabilized at relatively low level, increased anew on 1 April while no magma was erupted, followed on 2 April by a major distal eruption and on 5 April by a summit caldera collapse. Long-term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input.

  13. Mammoth Mountain, California broadband seismic experiment

    NASA Astrophysics Data System (ADS)

    Dawson, P. B.; Pitt, A. M.; Wilkinson, S. K.; Chouet, B. A.; Hill, D. P.; Mangan, M.; Prejean, S. G.; Read, C.; Shelly, D. R.

    2013-12-01

    Mammoth Mountain is a young cumulo-volcano located on the southwest rim of Long Valley caldera, California. Current volcanic processes beneath Mammoth Mountain are manifested in a wide range of seismic signals, including swarms of shallow volcano-tectonic earthquakes, upper and mid-crustal long-period earthquakes, swarms of brittle-failure earthquakes in the lower crust, and shallow (3-km depth) very-long-period earthquakes. Diffuse emissions of C02 began after a magmatic dike injection beneath the volcano in 1989, and continue to present time. These indications of volcanic unrest drive an extensive monitoring effort of the volcano by the USGS Volcano Hazards Program. As part of this effort, eleven broadband seismometers were deployed on Mammoth Mountain in November 2011. This temporary deployment is expected to run through the fall of 2013. These stations supplement the local short-period and broadband seismic stations of the Northern California Seismic Network (NCSN) and provide a combined network of eighteen broadband stations operating within 4 km of the summit of Mammoth Mountain. Data from the temporary stations are not available in real-time, requiring the merging of the data from the temporary and permanent networks, timing of phases, and relocation of seismic events to be accomplished outside of the standard NCSN processing scheme. The timing of phases is accomplished through an interactive Java-based phase-picking routine, and the relocation of seismicity is achieved using the probabilistic non-linear software package NonLinLoc, distributed under the GNU General Public License by Alomax Scientific. Several swarms of shallow volcano-tectonic earthquakes, spasmodic bursts of high-frequency earthquakes, a few long-period events located within or below the edifice of Mammoth Mountain and numerous mid-crustal long-period events have been recorded by the network. To date, about 900 of the ~2400 events occurring beneath Mammoth Mountain since November 2011 have

  14. Broadband Seismic Study of the Dominican Republic

    NASA Astrophysics Data System (ADS)

    Pulliam, J.; Polanco Rivera, E.; Pujols Guridy, R.; Huerfano Moreno, V. A.; Lopez, A. M.

    2014-12-01

    The Northeast Caribbean Plate Boundary Zone (NCPBZ) is characterized by oblique subduction of oceanic crust belonging to the North American Plate, a broad zone of deformation to accommodate strain, and the development of transform and normal faults on and around the island of Hispaniola. Other features may include the formation of a new microplates, rearrangement and aggregation of crustal fragments into new islands, and rotations of the microplates. Numerous issues regarding the nature and timing of formation of the features described above, their roles in regional tectonics and even whether they exist at all, remain unresolved. Our short-term goal is to better constraint lithospheric structure and identify active earthquake faults with a temporary broadband seismic network in the Dominican Republic. The oblique-subduction-to-strike-slip transition found in the NCPBZ is representative of numerous locales around the world, so lessons learned here may inform our understanding of plate tectonics broadly. In 2013-2014 we installed sixteen broadband seismic stations in the Dominican Republic. The temporary network will remain in place for two years. Data acquired by the temporary network will be integrated with data recorded by existing seismic facilities in the region and the combined dataset will be used for a series of analyses that will, collectively, allow us to image lithospheric structure and aid seismic hazard assessment for the island of Hispaniola. Preliminary results will be presented from the deployment, including regional earthquake locations and improved 1D Earth structure as well as plans for collaborations between regional seismic networks and local capacity-building.

  15. Dynamics of the 2007 Eruptions of Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station

    NASA Astrophysics Data System (ADS)

    Fontaine, Fabrice R.; Roult, Geneviève; Michon, Laurent; Barruol, Guilhem; Ferrazzini, Valérie; Di Muro, Andrea; Reymond, Dominique; Peltier, Aline; Staudacher, Thomas

    2014-05-01

    Seismic records from the RER very broad-band seismic station (La Réunion Island) belonging to the GEOSCOPE network are investigated to understand the eruptive succession (February to May) of Piton de la Fournaise and the caldera collapse episode of April 2007. Data first indicate that the short-lived, small volume, summit eruption of February 18 occurred during a phase of continuous inflation initiated in January 2007. Inflation decelerated around 2 weeks before a second short-lived small volume eruption on March 30-31 on the SE flank, almost simultaneous with a sudden, large deflation of the edifice. Deflation rate, which had stabilized at a relatively low level, increased anew on April 1 while no magma was emitted, followed on April 2 by a more distant and one of the most voluminous eruptions of the last two centuries at La Réunion Island. The RER station shows that very long period (VLP) and ultra long period (ULP) events developed during this period. Seven ULP events preceded the caldera collapse and 48 ones occurred during the caldera collapse over 9 days, most of which during the first 30 hours. A thorough examination of the seismic signals corrected for tide effects shows that each collapse event was coeval with VLP and ULP signals. Each individual collapse showed similar ULP and VLP signals characterized by periods of ~ 500 s and ~ 7 s, respectively. The back-azimuth of most ULP signals related to the caldera collapse points clearly toward the Dolomieu caldera. The strikingly constant duration of the VLP signals (around 20 s) related to the collapse events and their occurrence before the collapse initiation suggest a physical control of the volcanic edifice. Waveforms and spectrograms of the various caldera collapse events show very homogeneous patterns, suggesting a similar and repeating volcano-tectonic process for the formation of the VLP signals events. Although tilt may be responsible of part of the ULP signals observed during the collapse events, we

  16. Analysis of the ambient seismic noise at Bulgarian seismic stations

    NASA Astrophysics Data System (ADS)

    Dimitrova, Liliya; Nikolova, Svetlana

    2010-05-01

    Modernization of Bulgarian National Seismological Network has been performed during a month in 2005. Broadband seismometers and 24-bits digital acquisition systems with dynamic range more than 132dB type DAS130-01 produced by RefTek Inc. were installed at the seismic stations from the existing analog network. In the present study the ambient seismic noise at Bulgarian National Digital Seismological Network (BNDSN) stations is evaluated. In order to compare the performance of the network against international standards the detail analysis of the seismic noise was performed using software and models that are applied in the international practice. The method of McNamara and Bulland was applied and the software code PDFSA was used to determine power spectral density function (PSD) of the background noise and to evaluate the probability density function (PDF). The levels of the ambient seismic noise were determined and the full range of the factors influencing the quality of the data and the performance of a seismic station was analyzed. The estimated PSD functions were compared against two models for high (NHNM) and low (NLNM) noise that are widely used in seismological practice for seismic station monitoring qualities assessment. The mode PDF are used to prepare annual, seasonal, diurnal and frequency analyses of the noise levels at BNDSN stations. The annual analysis shows that the noise levels at the Northern Bulgarian stations are higher than the ones at Central and Southern stations for the microseisms' periods (1sec -7sec). It is well observable at SS PRV and PSN located near Black sea. This is due to the different geological conditions of the seismic stations as well. For the periods of "cultural" noise the power distribution depends on the type of noise sources and as a rule is related to human activities at or near the Earth surface. Seismic stations MPE, VTS and MMB have least mode noise levels and the noisiest stations are PGB, PVL и JMB. The seasonal

  17. The improved broadband Real-Time Seismic Network in Romania

    NASA Astrophysics Data System (ADS)

    Neagoe, C.; Ionescu, C.

    2009-04-01

    Starting with 2002 the National Institute for Earth Physics (NIEP) has developed its real-time digital seismic network. This network consists of 96 seismic stations of which 48 broad band and short period stations and two seismic arrays are transmitted in real-time. The real time seismic stations are equipped with Quanterra Q330 and K2 digitizers, broadband seismometers (STS2, CMG40T, CMG 3ESP, CMG3T) and strong motions sensors Kinemetrics episensors (+/- 2g). SeedLink and AntelopeTM (installed on MARMOT) program packages are used for real-time (RT) data acquisition and exchange. The communication from digital seismic stations to the National Data Center in Bucharest is assured by 5 providers (GPRS, VPN, satellite communication, radio lease line and internet), which will assure the back-up communications lines. The processing centre runs BRTT's AntelopeTM 4.10 data acquisition and processing software on 2 workstations for real-time processing and post processing. The Antelope Real-Time System is also providing automatic event detection, arrival picking, event location and magnitude calculation. It provides graphical display and reporting within near-real-time after a local or regional event occurred. Also at the data center was implemented a system to collect macroseismic information using the internet on which macro seismic intensity maps are generated. In the near future at the data center will be install Seiscomp 3 data acquisition processing software on a workstation. The software will run in parallel with Antelope software as a back-up. The present network will be expanded in the near future. In the first half of 2009 NIEP will install 8 additional broad band stations in Romanian territory, which also will be transmitted to the data center in real time. The Romanian Seismic Network is permanently exchanging real -time waveform data with IRIS, ORFEUS and different European countries through internet. In Romania, magnitude and location of an earthquake are now

  18. Background noise model development for seismic stations of KMA

    NASA Astrophysics Data System (ADS)

    Jeon, Youngsoo

    2010-05-01

    The background noise recorded at seismometer is exist at any seismic signal due to the natural phenomena of the medium which the signal passed through. Reducing the seismic noise is very important to improve the data quality in seismic studies. But, the most important aspect of reducing seismic noise is to find the appropriate place before installing the seismometer. For this reason, NIMR(National Institution of Meteorological Researches) starts to develop a model of standard background noise for the broadband seismic stations of the KMA(Korea Meteorological Administration) using a continuous data set obtained from 13 broadband stations during the period of 2007 and 2008. We also developed the model using short period seismic data from 10 stations at the year of 2009. The method of Mcmara and Buland(2004) is applied to analyse background noise of Korean Peninsula. The fact that borehole seismometer records show low noise level at frequency range greater than 1 Hz compared with that of records at the surface indicate that the cultural noise of inland Korean Peninsula should be considered to process the seismic data set. Reducing Double Frequency peak also should be regarded because the Korean Peninsula surrounded by the seas from eastern, western and southern part. The development of KMA background model shows that the Peterson model(1993) is not applicable to fit the background noise signal generated from Korean Peninsula.

  19. Continuous broadband seismic observation on the Greenland Ice Sheet under Greenland Ice Sheet monitoring Network

    NASA Astrophysics Data System (ADS)

    Tsuboi, Seiji; Kanao, Masaki; Tono, Yoko; Himeno, Tetsuto; Toyokuni, Genti; Childs, Dean; Dahl-Jensen, Trine; anderson, Kent

    2013-04-01

    We have installed the ice sheet broadband seismograph station, called ICE-S (DK.ICESG) in June 2011, in collaboration with IRIS Polar Services under the GreenLand Ice Sheet monitoring Network (GLISN), which is a new, international, broadband seismic capability for Greenland being implemented through the collaboration between Denmark, Canada, France, Germany, Italy, Japan, Norway, Poland, Switzerland, and the USA. The primary purpose of GLISN project is to define the fine structure and detailed mechanisms of glacial earthquakes within the Greenland Ice Sheet. These glacial earthquakes in the magnitude range 4.6-5.1 may be modeled as a large glacial ice mass sliding downhill several meters on its basal surface over duration of 30 to 60 seconds. Glacial earthquakes have been observed at seismic stations within Greenland (Larsen et al, 2006), but the coverage was very sparse and a broadband, real-time seismic network was needed to be installed throughout Greenland's Ice Sheet and perimeter. The National Institute for Polar Research and Japan Agency for Marine-Earth Science and Technology are members of GLISN project and we have started to operate ICESG station since 2011. The station is equipped with a CMG-3T broadband seismometer and a Quanterra Q330 data logger. We have visited the station again in May, 2012 and successfully retrieved one year of continuous records from the broadband seismometer and updated the telemetry system to eventually allow real time monitoring of the station. ICESG station is now daily sending 1 Hz continuous data over the iridium satellite system using RUDICS. The observed three component seismograms demonstrate that the quality of this ice sheet station is good enough to record not only local earthquakes around Greeland but also teleseismic earthquakes. We could record three component broadband seismograms for April 11, 2012 Off the west coast of Northern Sumatra earthquake (Mw8.6). These seismograms show high signal to noise ratio

  20. MOBB: Data Analysis from an Ocean Floor Broadband Seismic Observatory

    NASA Astrophysics Data System (ADS)

    Uhrhammer, R. A.; Dolenc, D.; Romanowicz, B.; Stakes, D.; McGill, P.; Neuhauser, D.; Ramirez, T.

    2003-12-01

    MOBB (Monterey bay Ocean floor Broad Band project) is a collaborative project between the Monterey Bay Aquarium Research Institute (MBARI) and the Berkeley Seismological Laboratory (BSL). Its goal is to install and operate a permanent seafloor broadband station as a first step towards extending the on-shore broadband seismic network in northern California, to the seaside of the North-America/Pacific plate boundary, providing improved azimuthal coverage for regional earthquake and structure studies. The MOBB station was installed on the seafloor in Monterey Bay, 40 km offshore, and at a depth of 1000m from the sea surface, in April 2002, and is completely buried under the seafloor level. The installation made use of MBARI's Point Lobos ship and ROV Ventana and the station currently records data autonomously. Dives are scheduled regularly (about every three months) to recover and replace the recording and battery packages. Some data were lost in the first half of 2003 due to hardware and software problems in the recording system. The ocean-bottom MOBB station currently comprises a three-component seismometer package (Guralp CMG-1T), a current-meter, a digital pressure gauge (DPG), and recording and battery packages. The seismometer package is mounted on a cylindrical titanium pressure vessel 54cm in height and 41 cm in diameter, custom built by the MBARI team and outfitted for underwater connection. Since the background noise in the near-shore ocean floor environment is high in the band pass of interest, for the study of regional and teleseismic signals, an important focus of this project is to develop methods to a posteriori increase signal to noise ratios, by deconvolving contributions from various sources of noise. We present results involving analysis of correlation of background noise with tide, ocean current and pressure records, combining data from MOBB and regional land based stations of the Berkeley Digital Seismic Network (BDSN). We also present preliminary

  1. Understanding the Dynamics of the February-April 2007 Eruptions of the Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station

    NASA Astrophysics Data System (ADS)

    Fontaine, F. R.; Roult, G. C.; Michon, L.; Barruol, G.; Ferrazzini, V.; di Muro, A.; Reymond, D.; Peltier, A.; Staudacher, T.

    2013-12-01

    Seismic records from the RER very broad-band seismic station (La Réunion Island) belonging to the GEOSCOPE network are investigated to understand the eruptive succession (February to May) of Piton de la Fournaise and the caldera collapse episode of April 2007. Data first indicate that the short-lived, small volume, summit eruption of February 18 occurred during a phase of continuous inflation initiated in end of January 2007. Inflation decelerated around 2 weeks before a second short-lived small volume eruption on March 30-31 on the SE flank, which was coeval with a sudden, large deflation of the edifice. Deflation rate, which was stabilized at a relatively low level, increased anew on April 1 while no magma was emitted, followed on April 2 by a distant and one of the most voluminous eruptions of the last two centuries at La Réunion Island. The RER station shows that very long period (VLP) and ultra long period (ULP) events developed during this period. Seven ULP events preceded the caldera collapse and 48 ones occurred during the caldera collapse over 9 days, most of which during the first 30 hours. A thorough examination of the seismic signal corrected from the tide effects shows that each collapse event was coeval with VLP and ULP signals. Each repeating individual collapse showed similar ULP and VLP signals characterized by periods of ~ 500 s and ~ 7 s, respectively. Polarization measurements (back-azimuth) of the ULP clearly point toward a source located beneath the Dolomieu crater. The strikingly constant duration of the VLP signals (around 20 s) related to the collapse events and occurring before the collapse initiation suggests a physical control of the volcanic edifice. Waveforms and spectrograms of the various caldera collapse events show very homogeneous patterns, suggesting a similar and repeating volcano-tectonic process for the formation of the VLP signals events. Although tilt may be responsible of part of the ULP signals observed during the

  2. Considerations of broadband seismic observation on Mars

    NASA Astrophysics Data System (ADS)

    Nishikawa, Y.; Kurita, K.; Araya, A.; Hori, T.; Kobayashi, N.; Shiraishi, H.; Kakuma, H.; Ishihara, Y.

    2010-12-01

    The surface of Mars has been extensively investigated and huge amount of data have been acquired such as high Res images. On the other hand interior of the Mars has been only weakly constrained by the mean density, the moment of inertia and gravity data. The size of core is poorly constrained and negatively correlated with the core density. High dissipation state is reported for the mantle by tidal interaction (Bills et al 2006), which is against a conventional view of small,cool planet. To clarify these points seismic observation on Mars is deadly needed. Japan Mars exploration project(MELOS) is now under discussion and it includes seismic measurements for determination the interior structure of Mars such as the core size, its state and attenuation in the mantle. Our plan is to install broadband high sensitivity seismometers,which are intended to detect continuous excitation of free oscillation by atmospheric turbulence. In this presentation we would like to show a basic design of broadband high sensitivity seismometer as well as environment protection designs. The basic parts are composed of a long period pendulum, laser interferometry and its control feedback electricity. As for the environment protection design,the following factors are important. 1. Surface condition. Martian surface is composed of stones gravels and sand. Drift is expected to occur due to the sudden change in ground slope. We need a device for self adjustment to keep the horizontal. 2. Temperature. Surface temperature at Martian equator is expected to vary between 190 to 300K. We have to consider changes in spring tension, thermal expansion of components and changes in circuit constants. 3. Surface wind. Inhomogeneously heated surface and topographic effect generate wind over 20m per second. We have to consider to lessen the effect of seismometer,even if we install the seismometer on the ground. 4. Radiation. Radiation that rains down on Mars is stronger because of thin atmosphere. Radiation

  3. Gran Canaria temporary broadband seismic network: an study of the seismicity and Earth structure

    NASA Astrophysics Data System (ADS)

    Almendros, Javier; de Lis Mancilla, Flor; Martinez-Arevalo, Carmen; Carmona, Enrique; Sanchez, Nieves; Heit, Benjamin; Garcia, Alicia; Martin-Leon, Rosa; Buontempo, Luisa; Yuan, Xiahoui

    2010-05-01

    The present project is a joint effort between different institutions to deploy a dense seismic network at Gran Canaria island (Canary Islands, Spain). The interstation distance is around 20 km. The broadband seismic network is composed of one permanent (Guralp CMG-3T 120 s) and five temporary stations (Guralp CMG-3ESP 60 s). The permanent station is a 120 s Guralp CMG-3T and belongs to the Canary Island Seismic Network, run by the Instituto Geográfico Nacional (IGN) of Spain. The temporary stations are 60 s Guralp CMG-3ESP, provided by the GFZ seismic pool. The deployment was carried out in December 2009. The stations will be recording during two years. The improvement of the seismic network allow us to tackle the following issues: the detection and analysis of any local seismicity of tectonic and/or volcanic origin at Gran Canaria island; to contribute to the understanding of the regional seismicity with special interest in the oceanic channel between Tenerife and Gran Canaria Island in collaboration with a project running a dense temporary seismic network in Tenerife; to study the crustal and upper mantle structure, under Gran Canaria to constrain the crustal structure, the source of the volcanism, and better sample the mantle discontinuities and anisotropy. To study the Earth structure, we use receiver function analysis, ambient seismic noise and SKS anisotropy techniques, This project is part of a long-term research of the crustal and the mantle structure of the Canary Islands, which has started with Gran Canaria and Tenerife Islands and will eventually continue with the rest of the archipelago. The origin of the Canary Islands is generally attributed to a broad mantle upwelling under a slow moving plate, resulting in spatially and temporally distributed volcanic activity and a large number of seamounts and islands. A controversial discussion has been going on about the factors that control the evolution of the volcanic edifices, the type of the melting

  4. Single-station monitoring of volcanoes using seismic ambient noise

    NASA Astrophysics Data System (ADS)

    De Plaen, Raphael S. M.; Lecocq, Thomas; Caudron, Corentin; Ferrazzini, Valérie; Francis, Olivier

    2016-08-01

    Seismic ambient noise cross correlation is increasingly used to monitor volcanic activity. However, this method is usually limited to volcanoes equipped with large and dense networks of broadband stations. The single-station approach may provide a powerful and reliable alternative to the classical "cross-station" approach when measuring variation of seismic velocities. We implemented it on the Piton de la Fournaise in Reunion Island, a very active volcano with a remarkable multidisciplinary continuous monitoring. Over the past decade, this volcano has been increasingly studied using the traditional cross-correlation technique and therefore represents a unique laboratory to validate our approach. Our results, tested on stations located up to 3.5 km from the eruptive site, performed as well as the classical approach to detect the volcanic eruption in the 1-2 Hz frequency band. This opens new perspectives to successfully forecast volcanic activity at volcanoes equipped with a single three-component seismometer.

  5. Geyser's Eruptive Activity in Broadband Seismic Records

    NASA Astrophysics Data System (ADS)

    Kugaenko, Yulia; Saltykov, Vadim

    2010-05-01

    A geyser is a spring characterized by intermittent discharge of water ejected turbulently and accompanied by a vapor phase (steam). The formation of geysers is due to particular hydrogeological conditions, which exist in only a few places on Earth, so they are a fairly rare phenomenon. The reasons of geyser periodicity and specifics of the activity for every particular geyser are not completely clear yet. So almost for all known geysers it is necessary to develop the personal model. In given study we first use seismic method for detection of possible hidden feature of geyser's eruptive activity in Kamchatkan Valley of the Geysers. Broadband seismic records of geyser generated signals were obtained in hydrothermal field. The Valley of the Geysers belongs to Kronotskiy State Natural Biosphere Reserve and the UNESCO World Natural Heritage Site "Volcanoes of Kamchatka". Neither seismological nor geophysical investigations were carried out here earlier. In September, 2009 seismic observation was organized in geyser's field by 24-bit digital output broadband seismometers (GURALP CMG-6TD flat velocity response 0.033-50 Hz). Four geysers were surveyed: the fountain type Big and Giant geysers; the cone type Pearl geyser and the short-period Gap geyser. Seismometers were set as possible close to the geyser's surface vent (usually at the distance near 3-5 m). Main parameters of the eruptions for the investigated geysers: - The Giant geyser is the most powerful among the regular active geysers in Kamchatkan Valley of the Geysers. The height of the fountain reaches 30 meters, the mass of water erupted is about 40-60 tons. The main cycle of activity varies significantly: in 1945 the intervals between eruptions was near 3 hours, nowadays it is 5-6 hours. As a geyser of fountain type, the Giant geyser erupts from the 2*3 m2 pool of water. - The Big geyser was flooded by the lake after the natural catastrophe (giant mud-stone avalanche, formed by landslide, bed into Geiyzernaya

  6. National Seismic Stations transducers and filters

    SciTech Connect

    Rodgers, P.W.; Hummell, M.

    1981-01-13

    The National Seismic Stations (NSS) instruments are being developed for seismic monitoring of regional and teleseismic events. They consist of two 3-component, broadband, borehole seismometers: the KS-36000 and the S-700, which is the backup for the KS-36000. Output is divided into frequency bands to reduce data loss due to saturation. Complete block diagrams of the KS-36000 and S-700 NSS seismometers and filters are presented. Both open-loop and closed-loop steady-state amplitude and phase curves are given. Without band-pass filters (but with shaping filters) the KS-36000 has a flat (i.e., between the -3dB points) velocity sensitivity from 0.03 to 23 Hz. With its shaping filters, the S-700 is flat from 0.2 to 40 Hz. The structure of the three band-pass filters (LP, MP, and SP) is superimposed on these velocity sensitivities. Passbands of the resulting overall velocity sensitivity for the KS-36000 are as follows: LP band = 0.01-0.05 Hz, MP band = 0.02-1.3 Hz, and SP band = 1-10 Hz. Step-function responses and phase and group delays are given for each of the bands. The MP-band step response is oscillatory due to its sharp, high-frequency cutoff, but an MP-band filter with a less abrupt cutoff eliminates the oscillation. To generate typical NSS output seismograms, velocity inputs from four representative seismic events were used: an underground nuclear test (..delta.. approx. = 3.6/sup 0/), a regional earthquake (..delta.. approx. = 20/sup 0/), a local earthquake (..delta.. approx. = 1.5/sup 0/), and a teleseismic earthquake (..delta.. approx. = 123/sup 0/). The velocity inputs for these events were obtained from the LLNL digital seismic network (DSS) around the Nevada Test Site (NTS). The seismograms resulting from each of the bands were satisfactory, although the low-frequency corner of the MP band should be increased in frequency to 0.08 Hz.

  7. Seismicity in West Iberia: small scale seismicity recording from a Dense Seismic Broadband Deployment in Portugal (WILAS Project)

    NASA Astrophysics Data System (ADS)

    Afonso Dias, Nuno; Custódio, Susana; Silveira, Graça; Carrilho, Fernando; Haberland, Christian; Lima, Vânia; Rio, Inês; Góngora, Eva; Marreiros, Célia; Morais, Iolanda; Vales, Dina; Fonseca, João; Caldeira, Bento; Villaseñor, Antonio

    2013-04-01

    Over the last years several projects targeted the lithospheric structure and its correlation with the surface topography, e.g. EarthSCOPE/USArray or TOPO-EUROPE. Two projects focused on the Iberian Peninsula, one giving particular attention to the southern collision margin (TOPO-MED) and the other to the central cratonic Massif (TOPO-IBERIA/IBERArray). These projects mostly rely on deployed dense seismic broadband (BB) networks with an average inter-station spacing of 60km, which strongly increases the available network spatial coverage. The seismicity recording in such networks is critical to access current rates of lithospheric deformation. Within the scope of project WILAS - West Iberia Lithosphere and Astenosphere Structure (PTDC/CTE-GIX/097946/2008), a 3-year project funded by the Portuguese Science & Technology Foundation (FCT), we deployed a temporary network of 30 BB stations in Portugal between 2010 and 2012, doubling the total number of operating BB stations. Together with the permanent and TOPO-IBERIA stations, the resulting networks provided a full and dense coverage of the Iberian Peninsula. The majority of the permanent stations in Portugal, aimed at the seismic surveillance, are located in the southern part of the country in result of the active tectonic convergence between Iberia and Africa. Therefore, the temporary stations were mainly deployed in the north of Portugal. These temporary stations allowed an improvement of the earthquake detection threshold. The detection of seismic events was based on the analysis of daily spectrograms of the entire network, the new events detected being analysed and included in the catalogue. The new detected events are located mainly in the north, with magnitudes as low as 0.5 ML and in the offshore in the Estremadura Spur. Some additional events were also located south of Portugal, between the Gorringe Bank and the Gulf of Cadiz, in this case the lower magnitudes being ~2.0ML. Focal mechanisms will also be

  8. Broadband seismology and small regional seismic networks

    USGS Publications Warehouse

    Herrmann, Robert B.

    1995-01-01

    In the winter of 1811-12, three of the largest historic earthquakes in the United States occurred near New Madrid, Missouri. Seismicity continues to the present day throughout a tightly clustered pattern of epicenters centered on the bootheel of Missouri, including parts of northeastern Arkansas, northwestern Tennessee, western Kentucky, and southern Illinois. In 1990, the New Madrid seismic zone/Central United States became the first seismically active region east of the Rocky Mountains to be designated a priority research area within the National Earthquake Hazards Reduction Program (NEHRP). This Professional Paper is a collection of papers, some published separately, presenting results of the newly intensified research program in this area. Major components of this research program include tectonic framework studies, seismicity and deformation monitoring and modeling, improved seismic hazard and risk assessments, and cooperative hazard mitigation studies.

  9. Development of the new very broadband compliance ocean bottom station

    NASA Astrophysics Data System (ADS)

    Rios, Celia; Dahm, Torsten; Bulow, Joachim; Winter, Sven

    2010-05-01

    In the frame of the EMSEIS Project* the University of Hamburg has developed two broadband compliance ocean bottom stations (BCSs). The objective was to create a station capable of acquire pressure and velocity data on the seafloor in the frequency range where compliance and infragravity waves are studied (30 - 500s). A triaxial seismometer STS-2, a differential pressure gauge, an absolute pressure sensor, and a MLS Geolon recorder were installed on a Hamburg free-fall ocean bottom station. The whole system works in a broad frequency range (between 0.005 Hz and 25 Hz) with a sampling frequency of 50 Hz. The maximum deployment depth is 6000 meters. The BCSs were created to acquire compliance data during short time deployments (20-100 hours). However, laboratory tests and field experiences indicate that instruments can continuously work during about 30 days. To secure the correct leveling of the seismic sensor, a two stage active leveling process was designed. In the first stage the mechanical leveling is performed and during the second stage the internal leveling is done and the masses are re-centered. Two electronic circuits were designed and connected to the recorder and the seismometer to control the complete process. The tasks of the circuits are: 1) determinate the number of cycles during a measurement which depend on the number of leveling signals sent by the recorder, 2) to generate the impulse to initiate the mechanical leveling phase, 3) to send the signal to produce the internal leveling and 4) to sent the signal to lock and unlock the masses to protect the equipment. To perform the mechanical leveling process the STS2 was mounted in a glass sphere on two gimbaled rings made of aluminum. Additionally, a retractile cube connected to a small motor was built-in the seismometer bottom. With the help of the motor, the cube can be extended to fix the seismometer to the sphere or can be retracted to allow the free pendulum motion of the seismometer in the sphere

  10. Coherent seismic sea-bottom profiling based on broadband signals

    NASA Astrophysics Data System (ADS)

    Lazarev, V. A.; Malekhanov, A. I.; Merklin, L. R.; Romanova, V. I.; Talanov, V. I.; Khil'ko, A. I.

    2013-11-01

    Experimental results of the seismic profiling with bottom penetration up to 1000 m based on broadband signals and conducted in the Caspian Sea sites are presented. Use has been made of synchronized sequences of probing pulses with linear frequency modulation at a frequency deviation of 50 to100 Hz. The pulses were emitted by a towed sound source of an original design (acoustic power up to 300 W, frequency ranged from 100 to 1000 Hz) and received by a standard digital seismic streamer. The processing of the signals involved the matched filtering of the individual pulses and the trajectory accumulation of a long sequence of pulses lengthwise the horizontal-homogeneous reflecting layers of the bottom structure. The adaptive stacking procedure taking into account the linear inclinations of the individual layers allowed us to enlarge the stacking interval by up to 100 pulses and to increase the effective depth and the spatial resolution of the seismic profiling, which gave us a total increase of more than 30 dB in the S/N ratio. In our view, the seismic profiling using low-power (about 100 W) and broadband (up to several hundred Hz) coherent sound sources represents a promising technology for decreasing the hazardous impact on aquatic ecosystems. The approach developed is an alternative to the conventional technology of marine seismic prospecting based on powerful pulse sources of the shock type (air guns, sparkers) in the low frequency range (less than ˜200 Hz).

  11. PQLX: A Software Tool to Evaluate Seismic Station Performance

    NASA Astrophysics Data System (ADS)

    McNamara, D. E.; Boaz, R. I.

    2006-12-01

    We present a new tool that will allow users to evaluate seismic station performance and characteristics by providing quick and easy transitions between visualizations of the frequency and time domains. The software is based on the probability density functions (PDF) of power spectral densities (PSD) (McNamara and Buland, 2004). The computed PSDs are stored in a MySQL database, allowing a user to access specific time periods of PSDs (PDF subsets) and time series segments through a GUI-driven interface. The power of the method and software lies in the fact that there is no need to screen the data for system transients, earthquakes or general data artifacts since they map into a background probability level. In fact, examination of artifacts related to station operation and episodic cultural noise allow us to estimate both the overall station quality and a baseline level of earth noise at each site. The output of this analysis tool is useful for both operational and scientific applications. Operationally, it is useful for characterizing the current and past performance of existing broadband stations, for conducting tests on potential new seismic station locations, for detecting problems with the recording system or sensors, and for evaluating the overall quality of data and meta-data. Scientifically, the tool allows for mining of PSDs for investigations on the evolution of seismic noise (see Aster et al., Hutt et al., Leeds et al., and Oneel et al., this meeting). The PDF algorithm and initial software were developed by the USGS as a part of the ANSS/GSN data and network QC system. Further development, supported by the IRIS Data Management Center, integrated the PDF algorithm into the IRIS QUACK system. The newest version, PQLX, combines the PDF system with the PQL time series viewing tool developed with support from IRIS PASSCAL. Currently, PQLX is operational at the USGS ANSS NOC and ASL for station performance monitoring.

  12. "13 BB star" - broadband seismic array at the edge of East European Craton in Poland

    NASA Astrophysics Data System (ADS)

    Polkowski, Marcin; Grad, Marek; Wilde-Piórko, Monika; Suchcicki, Jerzy; Arant, Tadeusz

    2014-05-01

    "13 BB star" is a dense array of 13 Reftek 151-120 broadband seismometers located in unpopulated forests in northern Poland - just on the edge of East European Craton. The shape of array was designed as a "star" with one central station and 12 station located on two circles (radius of about 30 and 60 km) around it. This geometry allows us to study seismic waves (in particular surface waves) incoming from all azimuths. Our "13 BB star" array stations are self powered (solar panels and batteries), equipped with local storage system and on-line transmission of seismic and auxiliary data using 2G and 3G cellular network. We also developed on-line application for monitoring array status (transmission, connections, power, temperature, etc.) and on-line data visualization. Main advantages of our array are: 1) 120s broadband seismometers recording with 100Hz sampling, 2) density of array - distances between neighboring stations does not exceed 30 km, 3) station placement in underground wells, 4) stations located in forests far (usually 2-3 km) from industries, roads, villages and other human activity. "13 BB star" started operating in July 2013 and since that time recorded several local, regional, and teleseismic events proving good array functionality. The scientific aim of the "13 BB star" project is development of a quantitative model of the lithosphere-asthenosphere-structure in the marginal zone of the East European Craton in northern Poland. New acquired data will be analyzed using integrated seismic methods, which will yield images of lithosphere-asthenosphere system hitherto unknown for this area. The knowledge of detailed structure of the cratonic lithosphere-asthenosphere system is crucial for the better understanding of the regional, as well as global mantle dynamics and evolution of the Earth's interior. This work was supported by NCN-grant DEC 2011/02/A/ST10/00284.

  13. Background noise spectra of global seismic stations

    SciTech Connect

    Wada, M.M.; Claassen, J.P.

    1996-08-01

    Over an extended period of time station noise spectra were collected from various sources for use in estimating the detection and location performance of global networks of seismic stations. As the database of noise spectra enlarged and duplicate entries became available, an effort was mounted to more carefully select station noise spectra while discarding others. This report discusses the methodology and criteria by which the noise spectra were selected. It also identifies and illustrates the station noise spectra which survived the selection process and which currently contribute to the modeling efforts. The resulting catalog of noise statistics not only benefits those who model network performance but also those who wish to select stations on the basis of their noise level as may occur in designing networks or in selecting seismological data for analysis on the basis of station noise level. In view of the various ways by which station noise were estimated by the different contributors, it is advisable that future efforts which predict network performance have available station noise data and spectral estimation methods which are compatible with the statistics underlying seismic noise. This appropriately requires (1) averaging noise over seasonal and/or diurnal cycles, (2) averaging noise over time intervals comparable to those employed by actual detectors, and (3) using logarithmic measures of the noise.

  14. Tsunami Observations on Hydrophones and Island Seismic Stations

    NASA Astrophysics Data System (ADS)

    Hanson, J. A.; Bowman, J. R.; Reasoner, C. L.; Shields, G.

    2007-12-01

    The tsunami generated by the great Indonesian earthquake of 26 December 2004 was recorded across a myriad of technologies, many of which had not been designed, nor expected, to record tsunami signals. We reported on the tsunami signals from this event observed at hydrophones, intended for nuclear test monitoring, and broadband seismometers that are part of the global seismic network (GSN). Our observations led us to examine more recently reported tsunamis and other historic tsunamis. The great Sumatra-Andaman earthquake (Mw 9.1) produced high-frequency (greater than 5 mHz) dispersed tsunami signals, in addition to the destructive wave, recorded by hydrophone stations offshore from Diego Garcia and Cape Leeuwin, Australia, and by many seismic stations in the Indian Ocean and on the coast of Antarctica. Dispersed energy was observed to 60 mHz. The details within the dispersed signal provided source information to which tide gauge data are insensitive. The source of high-frequency signals could be determined using event- to-station distances estimated from the dispersion. Fine structure in the tsunami signal indicated a possible secondary high-frequency source. The dispersion observations and modeling also identified individual reflector sources over basin-wide distances. Two other recent tsunamis were observed in the Indian Ocean. The 28 March 2005 earthquake (Mw 8.6) produced high-frequency tsunami waves (to 20 mHz) observed at the Diego Garcia hydrophone station and the AIS seismic station. In addition, the lower frequency, non-dispersed tsunami waves were seen at four other seismic stations. The Mw 7.7 earthquake on 17 July 2006 south of Java also generated high frequency tsunami waves (to 10 mHz). Clear, dispersed signals were observed on hydrophone stations and seismic stations at the Cocos-Keeling Islands, and Casey, Antarctica. The first arriving energy is consistent with a source located at the earthquake epicenter. However, the strongest signals at Cocos

  15. Quantifying the Benefits of Shallow Posthole Installation for the Future French Permanent Broadband Stations

    NASA Astrophysics Data System (ADS)

    Vergne, J.; Charade, O.; Bonaime, S.; Louis-Xavier, T.; Arnold, B.

    2015-12-01

    In the framework of the RESIF (réseau sismologique et géodésique français) infrastructure, more than one hundred new permanent broadband stations have to be deployed in metropolitan France within the forthcoming years. This requires a standardized installation method able to provide good noise level performance at a reasonable cost, especially for the 60 percent of stations that we expect to be settled in open environments. During the last two years we tested various types of sensor's hosting infrastructures with a strong focus on recently released posthole sensors that can be deployed at the bottom of shallow boreholes. Tests were performed at 3 different sites (two GEOSCOPE stations and a dedicated open-field prototype site) with geological conditions spanning from hard rocks to very soft soils. On each site, posthole sensors were deployed at different depths, from the surface to a maximum of 20m deep, and in different types of casing. Moreover, a reference sensor, either installed in a tunnel, a cellar or a seismic vault, has been operated continuously. We present a comprehensive comparison of the seismic noise level measured in the different hosting infrastructures and for several frequency bands corresponding to various sources of noise. At high and low frequencies, seismic noise level in some boreholes equals or outperforms the one obtained for the reference sensors. Between 0.005 and 0.05Hz, we observe a strong decrease of seismic noise level on the horizontal components in the deepest boreholes compared to near surface installations. This improvement can reach up to 30dB and is mostly due to a reduction in tilt noise induced by wind or local pressure variations. However, the absolute noise level that can be achieved clearly depends on the local geology. All these tests, together with estimated installation costs, point toward the deployment of sensors in shallow boreholes at the future French broadband stations located in open environments.

  16. Sensor Emplacement Techniques and Seismic Noise Analysis for USArray Transportable Array Seismic Stations

    NASA Astrophysics Data System (ADS)

    Frassetto, A.; Busby, R. W.; Hafner, K.; Woodward, R.; Sauter, A.

    2013-12-01

    In preparation for the upcoming deployment of EarthScope's USArray Transportable Array (TA) in Alaska, the National Science Foundation (NSF) has supported exploratory work on seismic station design, sensor emplacement, and communication concepts appropriate for this challenging high-latitude environment. IRIS has installed several experimental stations to evaluate different sensor emplacement schemes both in Alaska and in the lower-48 of the U.S. The goal of these tests is to maintain or enhance a station's noise performance while minimizing its footprint and the weight of the equipment, materials, and overall expense required for its construction. Motivating this approach are recent developments in posthole broadband seismometer design and the unique conditions for operating in Alaska, where there are few roads, cellular communications are scarce, most areas are only accessible by small plane or helicopter, and permafrost underlies much of the state. We will review the methods used for directly emplacing broadband seismometers in comparison to the current methods used for the lower-48 TA. These new methods primarily focus on using a portable drill to make a bored hole three to five meters, beneath the active layer of the permafrost, or by coring 1-2 meters deep into surface bedrock. Both methods are logistically effective in preliminary trials. Subsequent station performance has been assessed quantitatively using probability density functions summed from power spectral density estimates. These are calculated for the continuous time series of seismic data recorded for each channel of the seismometer. There are five test stations currently operating in Alaska. One was deployed in August 2011 and the remaining four in October 2012. Our results show that the performance of seismometers in Alaska with auger-hole or core-hole installations can sometimes exceed that of the quietest TA stations in the lower-48, particularly horizontal components at long periods. A

  17. Seismic Earth: Array Analysis of Broadband Seismograms

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Nolet, Guust

    Seismology is one of the few means available to Earth scientists for probing the mechanical structure of the Earth's interior. The advent of modern seismic instrumentation at the end of the 19th century and its installation across the globe was shortly followed by mankind's first general understanding of the Earth's interior: The Croatian seismologist Andrija Mohorovičić discovered the crust-mantle boundary in central Europe in 1909, the German Beno Gutenberg determined the radius of the Earth's core in 1913, Great Britian's Sir Harold Jeffreys established its fluid character by 1926, and the Dane Inge Lehman discovered the solid inner core in 1936. It is notable that seismology, even in its earliest days, was an international science. Unlike much of the Earth sciences, seismology has its roots in physics, notably optics (many university seismology programs are, or initially were, attached to meteorology, astronomy, or physics departments), and draws from the literatures of imaging systems and statistical communications theory developed by, or employed in, astronomy, electrical engineering, medicine, ocean acoustics, and nondestructive materials testing. Seismology has close ties to petro-physics and mineral physics, the measurements of the disciplines being compared to infer the chemical and physical structure of the Earth's interior.

  18. A New Design of Seismic Stations Deployed in South Tyrol

    NASA Astrophysics Data System (ADS)

    Melichar, P.; Horn, N.

    2007-05-01

    When designing the seismic network in South Tyrol, the seismic service of Austria and the Civil defense in South Tyrol combined more that 10 years experience in running seismic networks and private communication systems. In recent years the high data return rate of > 99% and network uptime of > 99.% is achieved by the combination of high quality station design and equipment, and the use of the Antelope data acquisition and processing software which comes with suite of network monitoring & alerting tools including Nagios, etc. The new Data Center is located in city of Bolzano and is connected to the other Data Centers in Austria, Switzerland, and Italy for data back up purposes. Each Data Center uses also redundant communication system if the primary system fails. When designing the South Tyrol network, new improvements were made in seismometer installations, grounding, lighting protection and data communications in order to improve quality of data recorded as well as network up-time, and data return. The new 12 stations are equipped with 6 Channels Q330+PB14f connected to STS2 + EpiSensor sensor. One of the key achievements was made in the grounding concept for the whole seismic station - and aluminum boxes were introduced which delivered Faraday cage isolation. Lightning protection devices are used for the equipment inside the aluminum housing where seismometer and data logger are housed. For the seismometer cables a special shielding was introduced. The broadband seismometer and strong-motion sensor are placed on a thick glass plate and therefore isolated from the ground. The precise seismometer orientation was done by a special groove on the glass plate and in case of a strong earthquake; the seismometer is tide up to the base plate. Temperature stability was achieved by styrofoam sheets inside the seismometer aluminum protection box.

  19. Broadband Seismic Investigations of the Upper Mantle Beneath the Vienna and Pannonian Basins

    NASA Astrophysics Data System (ADS)

    Dando, B. D.; Stuart, G. W.; Houseman, G. A.; Team, C.

    2008-12-01

    The Carpathian Basins Project (CBP) aims to understand the origin of the Miocene-age extensional basins contained within the compressional arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from approximately 341 teleseismic events. The 3-D velocity variation obtained by tomographic inversion of the P-wave travel-time residuals shows an approximately linear belt of fast material of width about 100 km, orientated WNW-ESE beneath the western Pannonian Basin at sub-lithospheric depths. This feature is apparently continuous with structure beneath the Eastern Alps, but becomes more diffuse into the transition zone. Our initial interpretation of these fast velocities is in terms of mantle downwelling related to the early collision of Adria and Europe. We use receiver functions to assess crustal structure variations. We also determine SKS anisotropy; regionally SKS varies systematically in direction, with a delay time of about 1.0s. E-W fast directions above the fast tomographic anomaly change to NW-SE across the Great Hungarian Plane and the Vienna Basin.

  20. Seismic source and structure estimation in the western Mediterranean using a sparse broadband network

    NASA Astrophysics Data System (ADS)

    Thio, Hong Kie; Song, Xi; Saikia, Chandan K.; Helmberger, Donald V.; Woods, Bradley B.

    1999-01-01

    We present a study of regional earthquakes in the western Mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations. The results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty, as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations. The area consists of several contrasting geological provinces with distinct seismic properties, which complicates the modeling of seismic wave propagation. We started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces. We found variations of crustal thickness ranging from 45 km under the Atlas and Betic mountains and 37 km under the Saharan shield, to 20 km for the oceanic crust of the western Mediterranean Sea, which is consistent with earlier works. Throughout most of the region, the upper mantle velocities are low which is typical for tectonically active regions. The most complex areas in terms of wave propagation are the Betic Cordillera in southern Spain and its north African counterparts, the Rif and Tell Atlas mountains, as well as the Alboran Sea, between Spain and Morocco. The complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion. We used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism. We found that this method, which is in use in many parts of the world, works very well, provided that data from several stations are available. In order to study the events in the region using very few broadband stations or even a single station

  1. Temporal variations in Global Seismic Stations ambient noise power levels

    USGS Publications Warehouse

    Ringler, A.T.; Gee, L.S.; Hutt, C.R.; McNamara, D.E.

    2010-01-01

    Recent concerns about time-dependent response changes in broadband seismometers have motivated the need for methods to monitor sensor health at Global Seismographic Network (GSN) stations. We present two new methods for monitoring temporal changes in data quality and instrument response transfer functions that are independent of Earth seismic velocity and attenuation models by comparing power levels against different baseline values. Our methods can resolve changes in both horizontal and vertical components in a broad range of periods (∼0.05 to 1,000 seconds) in near real time. In this report, we compare our methods with existing techniques and demonstrate how to resolve instrument response changes in long-period data (>100 seconds) as well as in the microseism bands (5 to 20 seconds).

  2. Site selection for the future stations of the french permanent broadband network

    NASA Astrophysics Data System (ADS)

    Vergne, Jérôme; Charade, Olivier

    2013-04-01

    RESIF (REseau SIsmologique et géodésique Français) is a new French research infrastructure dedicated to the observation of earth deformation based on seismic and geodetic instruments mainly located in France. One of its major component, called RESIF-CLB (Construction Large Bande), is devoted to the evolution of the permanent seismic broadband network in metropolitan France with the objective to complement the 45 existing stations with ~155 new stations within the next eight years. This network will be used for various scientific objectives including deep structures imaging and national seismicity monitoring. The chosen network topology consists in a backbone of homogeneously distributed stations (long wavelength array) completed by additional stations in seismically active regions. Management of the RESIF-CLB project is carried out by the technical division of INSU (Institut National des Sciences de l'Univers) who will rely on eight regional observatories and the CEA-LDG for the construction and operation of the stations. To optimize the performance of the network, we put a strong emphasis on the standardization of the stations in term of vault types, scientific and technical instrumentation and operation procedures. We also set up a procedure for site selection requiring that every potential site has to be tested for at least 3 weeks with a minimalist installation. Analysis of the continuous ambient noise records is then included in a standardized report submitted to all committed partners for acceptance. During the last two years, about 60 potential new sites have been tested, spanning various places and environments. We present a review of the seismic noise measurements at these sites and discuss the influence of different types of noise sources depending on the frequency band of interest. For example, we show that regional population distribution can be used as a proxy to infer the noise level at frequencies higher than 1 Hz. Based on similar noise analyses

  3. MOBB: a permanent ocean floor broadband seismic observatory in Monterey Bay, California

    NASA Astrophysics Data System (ADS)

    Uhrhammer, R.; Romanowicz, B.; Stakes, D.; Neuhauser, D.; McGill, P.; Ramirez, T.

    2003-04-01

    The Monterey ocean bottom broadband station (MOBB) was installed on the seafloor in Monterey Bay, 40 km offshore, and at a depth of 1000m from the sea surface, on April 9-11, 2002. Its success capitalizes on the experience gained in the 1997 International MOISE experiment, conducted under similar conditions. The deployment took place during 3 dives on consecutive days and made use of MBARI's Point Lobos ship and ROV Ventana. The station is currently recording data autonomously. Eventually, it will be linked to the planned (and recently funded) MARS (Monterey Accelerated Research System; \\url {http://www.mbari.org/mars/}) cable and provide real-time, continuous seismic data to be merged with the rest of the northern California real-time seismic system. The data are archived at the NCEDC for on-line availability, as part of the Berkeley Digital Seismic Network (BDSN). The ocean-bottom MOBB station currently comprises a three-component seismometer package, a current-meter, a DPG, and recording and battery packages. The seismic package contains a low-power (2.2W), three-component CMG-1T broadband seismometer system, built by Guralp, Inc., with a three-component 24-bit digitizer, a leveling system, and a precision clock. The seismometer package is mounted on a cylindrical titanium pressure vessel 54cm in height and 41 cm in diameter, custom built by the MBARI team and outfitted for underwater connection. Data recovery dives, during which the recording and battery package will be exchanged are planned every three months for the next 3 years. Three such dives have already taken place, on 06/27/02, 09/20/02 and on 01/07/03. Due to a software problem, data were lost during the time period 07/01/02 and 09/20/02. Many regional and teleseismic earthquakes have been well recorded and the mass position signals indicate that the instruments have progressively settled. Preliminary analysis of data retrieved during the 2002 summer and winter dives will be presented. In particular

  4. The SCEDC Seismic Station Information System software: Database for Populating, Archiving, and Distributing Seismic Station Metadata

    NASA Astrophysics Data System (ADS)

    Chowdhury, F. R.; Yu, E.; Hauksson, E.; Given, D.; Thomas, V. I.; Clayton, R. W.

    2010-12-01

    The Station Information System (SIS) is a database-driven system used by the Southern California Seismic Network (SCSN) to store and distribute station metadata. This abstract concerns the User Interface portion of SIS. The User Interface (UI) is a web application that enables authenticated users to view and edit the station metadata. New features have recently been added to SIS in order to facilitate station upgrades for the American Recovery and Reinvestment Act (ARRA). In particular, SIS now stores an extended range of metadata that encompasses not only station/channel response information but also operations and telemetry information. Typical activities for stations operation that are handled by SIS include powersystem upgrades, and inventory management such as tracking ownership and firmware settings. The UI also enables users to track and report instrumentation problems that may affect the station/channel response. In addition, progress has been made in developing a framework for storing station telemetry path information. The accelerated ARRA station upgrade schedule requires SCSN operators to log more than one response change per day in SIS; the updated station metadata is automatically generated and available for use by the ANSS Quake Monitoring System (AQMS).

  5. Spectral Analysis of Broadband Seismic Array Data, Tien Shan

    NASA Astrophysics Data System (ADS)

    Shamshy, S.; Pavlis, G. L.

    2003-12-01

    We used a spectral analysis method to examine amplitude variations of body waves recorded in the Tien Shan region of central Asia. We used broadband data from the Kyrgyz Network (KNET), Kazakhstan Network (KZNET), and from a set of temporary, PASSCAL stations operated from 1997-2000 we refer to as the Ghengis array. A spectral ratio method similar to that used by Wilson and Pavlis (2000) was employed, but with station AAK used as a reference instead of the array median. Spectral ratios were estimated for all teleseismic events and a larger, intermediate depth events from the Hindu-Kush region for all three-components of ground motion and total signal strength on all components. Results are visualized by maps of amplitude for various frequency bands and through the 4-D animation method introduced by Wilson and Pavlis (2000). Data from Hindu-Kush events showed amplitude variations as much as a factor of 100 across the study area with a strong frequency dependence. The largest variations were at the highest frequencies observed near 15 Hz. Stations in the northwestern part of the Tien Shan array show little variation in amplitude relative to the reference station, AAK. In the central and eastern part of the array, the amplitude estimates are significantly smaller at all frequencies. In contrast, for stations in the western Tien Shan near the Talas-Fergana Fault, and the southern Tien Shan near the Tarim Basin, the amplitude values become much larger than the reference site. The teleseismic data show a different pattern and show a somewhat smaller, overall amplitude variation at comparable frequencies. The northern part of the array again shows small variations relative to the reference stations. There are some amplifications in the southern stations of the array, especially in the Tarim Basin. The higher frequency observations that show large amplifications at stations in the Tarim Basin are readily explained by site effects due to the thick deposits of sediments

  6. Broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches

    NASA Astrophysics Data System (ADS)

    Kumagai, H.; Nakano, M.; Maeda, T.; Yepes, H.; Palacios, P.; Ruiz, M. C.; Arrais, S.; Vaca, M.; Molina, I.; Yamashina, T.

    2009-12-01

    We systematically used two approaches to analyze broadband seismic signals observed at active volcanoes: one is waveform inversion of very-long-period (VLP) signals in the frequency domain assuming possible source mechanisms; the other is a source location method of long-period (LP) and tremor using their amplitudes. The deterministic approach of the waveform inversion is useful to constrain the source mechanism and location, but is basically only applicable to VLP signals with periods longer than a few seconds. The source location method uses seismic amplitudes corrected for site amplifications and assumes isotropic radiation of S waves. This assumption of isotropic radiation is apparently inconsistent with the hypothesis of crack geometry at the LP source. Using the source location method, we estimated the best-fit source location of a VLP/LP event at Cotopaxi using a frequency band of 7-12 Hz and Q = 60. This location was close to the best-fit source location determined by waveform inversion of the VLP/LP event using a VLP band of 5-12.5 s. The waveform inversion indicated that a crack mechanism better explained the VLP signals than an isotropic mechanism. These results indicated that isotropic radiation is not inherent to the source and only appears at high frequencies. We also obtained a best-fit location of an explosion event at Tungurahua when using a frequency band of 5-10 Hz and Q = 60. This frequency band and Q value also yielded reasonable locations for the sources of tremor signals associated with lahars and pyroclastic flows at Tungurahua. The isotropic radiation assumption may be valid in a high frequency range in which the path effect caused by the scattering of seismic waves results in an isotropic radiation pattern of S waves. The source location method may be categorized as a stochastic approach based on the nature of scattering waves. We further applied the waveform inversion to VLP signals observed at only two stations during a volcanic crisis

  7. Local magnitude determinations for intermountain seismic belt earthquakes from broadband digital data

    USGS Publications Warehouse

    Pechmann, J.C.; Nava, S.J.; Terra, F.M.; Bernier, J.C.

    2007-01-01

    The University of Utah Seismograph Stations (UUSS) earthquake catalogs for the Utah and Yellowstone National Park regions contain two types of size measurements: local magnitude (ML) and coda magnitude (MC), which is calibrated against ML. From 1962 through 1993, UUSS calculated ML values for southern and central Intermountain Seismic Belt earthquakes using maximum peak-to-peak (p-p) amplitudes on paper records from one to five Wood-Anderson (W-A) seismographs in Utah. For ML determinations of earthquakes since 1994, UUSS has utilized synthetic W-A seismograms from U.S. National Seismic Network and UUSS broadband digital telemetry stations in the region, which numbered 23 by the end of our study period on 30 June 2002. This change has greatly increased the percentage of earthquakes for which ML can be determined. It is now possible to determine ML for all M ???3 earthquakes in the Utah and Yellowstone regions and earthquakes as small as M <1 in some areas. To maintain continuity in the magnitudes in the UUSS earthquake catalogs, we determined empirical ML station corrections that minimize differences between MLs calculated from paper and synthetic W-A records. Application of these station corrections, in combination with distance corrections from Richter (1958) which have been in use at UUSS since 1962, produces ML values that do not show any significant distance dependence. ML determinations for the Utah and Yellowstone regions for 1981-2002 using our station corrections and Richter's distance corrections have provided a reliable data set for recalibrating the MC scales for these regions. Our revised ML values are consistent with available moment magnitude determinations for Intermountain Seismic Belt earthquakes. To facilitate automatic ML measurements, we analyzed the distribution of the times of maximum p-p amplitudes in synthetic W-A records. A 30-sec time window for maximum amplitudes, beginning 5 sec before the predicted Sg time, encompasses 95% of the

  8. Passive, broad-band seismic measurements for geothermal exploration : The GAPSS experiment

    NASA Astrophysics Data System (ADS)

    Saccorotti, Gilberto; Piccinini, Davide; Zupo, Maria; Mazzarini, Francesco; Cauchie, Lena; Chiarabba, Claudio; Piana Agostinetti, Nicola

    2014-05-01

    Passive seismological imaging techniques based on either transient (earthquakes) or sustained (background noise) signals can provide detailed descriptions of subsurface attributes as seismic velocity, attenuation, and anisotropy. However, the correspondence between these parameters and the physical properties of crustal fluids is still ambiguous. Moreover, the resolving capabilities and condition of applicability of emerging techniques such as the Ambient Noise Tomography are still to be investigated thoroughly. Following these arguments, a specific project (GAPSS-Geothermal Area Passive Seismic Sources) was planned, in order to test passive exploration methods on a well-known geothermal area, namely the Larderello-Travale Geothermal Field (LTGF). This geothermal area is located in the western part of Tuscany (Italy), and it is the most ancient geothermal power field of the world. Heat flow in this area can reach local peaks of 1000 mW/m3. The deep explorations in this area showed a deeper reservoir (3000 to 4000 m depth) located within the metamorphic rocks in the contact aureole of the Pliocene-Quaternary granites; it is characterized by a wide negative gravimetric anomaly, interpreted as partially molten granite at temperatures of 800°C. From seismic surveys the K-marker K (pressurized horizons) was found at depths between 3 and 7 km. The structural grain of the geothermal field is characterized by N-W trending and N-E dipping normal faults whose activity lasts since the Pliocene. GAPSS lasted from early May, 2012, through October, 2013. It consisted of up to 20 temporary seismic stations, complemented by two permanent stations from the National Seismic Network of Italy. The resulting array has an aperture of about 50 Km, with station spacings between 2 and 50 km. Stations are equipped with either broadband (40s and 120s) or intermediate-period (5s), 3-components seismometers. LTGF is seismically active. During the first 10 months of measurements, we located

  9. Crustal thickness in central Europe from single-station seismic noise autocorrelation analysis

    NASA Astrophysics Data System (ADS)

    Becker, Gesa; Knapmeyer-Endrun, Brigitte

    2016-04-01

    The InSight mission to Mars will place a single three-component seismometer on the planet's surface, requiring the application of single-station methods. In addition, seismicity on Mars is likely less abundant than on Earth, making it important to also use the available seismic noise. For these reasons different approaches of seismic noise autocorrelation have been tested with broadband three-component datasets from 12 stations across central Europe. These stations cover varying Moho depths of ca. 25-50 km depth. With the help of the autocorrelations, reflected body waves are extracted in order to estimate the crustal thickness at each station. This is of special relevance for Mars, where average crustal thickness is uncertain by a factor of two. The different approaches used are waterlevel normalized autocorrelation, with and without application of a short-term and long-term average filter to the spectrum of the data prior to autocorrelation, and phase autocorrelation. These approaches are compared and analyzed. Estimates for the Moho depths are made from the lag times of the reflected P-waves and compared to available Moho depth values at the stations. Due to the availability of three-component data these estimates can be cross-validated and in some cases not only P-wave reflections, but also possible S-wave and multiple reflections can be identified. The estimates compare well with the general trend of Moho depth expected for these stations. The consistency of results is further investigated by comparing different stations of the GERES array (aperture 2 km), which also allows to examine results for closely located broad-band and short-period stations side by side.

  10. Swiss AlpArray: deployment of the Swiss AlpArray temporary broad-band stations and their noise characterization

    NASA Astrophysics Data System (ADS)

    Molinari, Irene; Kissling, Edi; Clinton, John; Hetényi, György; Šipka, Vesna; Stipćević, Josip; Dasović, Iva; Solarino, Stefano; Wéber, Zoltán; Gráczer, Zoltán; Electronics Lab, SED

    2016-04-01

    One of the main actions of the AlpArray European initiative is the deployment of a dense seismic broad-band network, that complements the existing permanent stations. This will ensure a spatially homogeneous seismic coverage of the greater Alpine area for at least two years, allowing a great number of innovative scientific works to be carried out. Our contribution to the AlpArray Seismic Network consists in the deployment of 24 temporary broad-band stations: three in Switzerland, twelve in Italy, three in Croatia, three in Bosnia and Herzegovina and three in Hungary. This deployment is lead by ETH Zurich and founded by the Swiss-AlpArray Sinergia programme by SNSF, and is the result of a fruitful collaboration between five research institutes. Stations were installed between Autumn and Winter 2015. Our installations are both free field and in-house and consist of 21 STS-2 and 3 Trillium Compact sensors equipped with Taurus digitizers and 3G telemetry sending data in real time to the ETH EIDA node. In this work, we present sites and stations setting and we discuss in details the characteristics in terms of site effects and noise level of each station. In particular we analyse the power spectral density estimates investigating the major source of noise and the background noise related to seasons, time of the day, human activities and type of installation. In addition we will show examples of data usage - i.e. earthquake locations, noise cross correlations, measures of surface wave dispersion curves. We thanks the Swiss AlpArray Field Team: Blanchard A., Erlanger E. D., Jarić D., Herak D., M. Herak, Hermann M., Koelemeijer P. J., Markušić S., Obermann A., Sager K., Šikman S., Singer J., Winterberg S. SED Electronic Lab: Barman S., Graf P., Hansemann R., Haslinger F., Hiemer S., Racine R., Tanner R., Weber F.

  11. The High Lava Plains Broadband Seismic Experiment: Objectives, Status and Preliminary Results

    NASA Astrophysics Data System (ADS)

    James, D. E.; Fouch, M.; Eager, K.; Nair, S.; Roth, J.; Warren, L.; Beghein, C.; West, J.; Carlson, R.; Johnson, J.; Golden, S.

    2006-12-01

    The High Lava Plains (HLP) Project is a multi-disciplinary program to study the structure and formation of the high lava plains volcanic lineament, the most prominent feature of the actively evolving continental lithosphere in central and eastern Oregon. This region in the Pacific Northwest represents one of the most accessible, yet least understood, examples worldwide of the tectonomagmatic consequences of plate margin restructuring on the development of continental lithosphere. The confusing and complex tectonomagmatic evolution there has been variously ascribed to the Yellowstone plume, back-arc subduction processes, Basin and Range extension, or asthenospheric inflow along the migrating edge of the descending Juan de Fuca (formerly Farallon) plate. Various aspects of each of these processes are either mutually exclusive or apparently inconsistent with observations, but the seismic data that could resolve key questions of tectonomagmatic development have been conspicuously absent. The HLP Seismic Experiment is organized around multi-level broadband and active source seismic studies of the crust and mantle beneath young continent now largely blanketed with late Cenozoic volcanic rocks. The dense broadband array, when fully configured, will consist of about 170 stations in a region ~ 500 x 350 km. The high station density will make it possible to resolve fine-scale structures in the crust and mantle beneath the extensive region of post-17 Ma volcanism and at its margins with Proterozoic North America, the Northern Great Basin, and Cascadia with detail well beyond the capabilities of the more sparse EarthScope USArray Transportable Array. Synthetic resolution tests of tomographic images demonstrate sharply contrasting capabilities between the two arrays, particularly for imaging localized low-velocity features in the uppermost mantle. While the full HLP array is not scheduled for deployment until late spring, 2007, the installation of a skeletal array began in

  12. Direct Burial Broadband Seismic Instrumentation that are Rugged and Tilt Tolerant for Polar Environments

    NASA Astrophysics Data System (ADS)

    Parker, Tim; Winberry, Paul; Huerta, Audrey; Bainbridge, Geoff; Devanney, Peter

    2016-04-01

    The integrated broadband Meridian Posthole and Compact seismic systems have been engineered and tested for extreme polar environments. Ten percent of the Earth's surface is covered in glacial ice and the dynamics of these environments is a strategic concern for all. The development for these systems was driven by researchers needing to densify observations in ice covered regions with difficult and limited logistics. Funding from an NSF MRI award, GEOICE and investment from the vendor enabled researchers to write the specifications for a hybrid family of instruments that can operate at -55C autonomously with very little power, 1 watt for the Meridian Compact system and 1.5 watts for the Meridian 120PH. Tilt tolerance in unstable ice conditions was a concern and these instruments have a range of up to +/-5 degrees. The form factor, extreme temperature tolerance and power load of the instruments has reduced the bulk of a complete station by 1/2 and simplified installation greatly allowing more instruments to be deployed with limited support and a lighter logistical load. These systems are being tested in the Antarctic at SouthPole Station and McMurdo for the second year and the investment has encouraged other instrument and power system vendors to offer polar rated equipment including telemetry for ancillary support.

  13. Seismic evidence for an ancient rift beneath the cumberland plateau, Tennessee: A detailed analysis of broadband teleseismic P waveforms

    SciTech Connect

    Owens, T.J.; Zandt, G.; Taylor, S.R.

    1984-09-10

    Broadband receiver functions developed from teleseismic P waveforms recorded on the midperiod passband of Regional Seismic Test Network station RSCP are inverted for vertical velocity structure beneath the Cumberland Plateau, Tennessee. The detailed broadband receiver functions are obtained by stacking source-equalizd horizontal components of teleseismic P waveforms. The resulting receiver functions are most sensitive to the shear velocity structure near the station. A time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin, flat-lying, homogeneous layers. Lateral changes in structure are identified by examining azimuthal variations in the vertical structure. The results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the East Continent Gravity High located northeast of RSCP. The results from events arriving from the northeast show a high-velocity midcrustal layer not present in results from the southeast azimuth. This velocity structure can be shown to support the idea that this feature is part of a Keweenawan rift system. Another interesting feature of the derived velocity models is the indication that the crust-mantle boundary beneath the Cumberland Plateau is a thick, probably laminated transition zone between the depths of 40 and 55 km, a result consistent with interpretations of early refraction work in the area.

  14. MC Kernel: Broadband Waveform Sensitivity Kernels for Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Stähler, Simon C.; van Driel, Martin; Auer, Ludwig; Hosseini, Kasra; Sigloch, Karin; Nissen-Meyer, Tarje

    2016-04-01

    We present MC Kernel, a software implementation to calculate seismic sensitivity kernels on arbitrary tetrahedral or hexahedral grids across the whole observable seismic frequency band. Seismic sensitivity kernels are the basis for seismic tomography, since they map measurements to model perturbations. Their calculation over the whole frequency range was so far only possible with approximative methods (Dahlen et al. 2000). Fully numerical methods were restricted to the lower frequency range (usually below 0.05 Hz, Tromp et al. 2005). With our implementation, it's possible to compute accurate sensitivity kernels for global tomography across the observable seismic frequency band. These kernels rely on wavefield databases computed via AxiSEM (www.axisem.info), and thus on spherically symmetric models. The advantage is that frequencies up to 0.2 Hz and higher can be accessed. Since the usage of irregular, adapted grids is an integral part of regularisation in seismic tomography, MC Kernel works in a inversion-grid-centred fashion: A Monte-Carlo integration method is used to project the kernel onto each basis function, which allows to control the desired precision of the kernel estimation. Also, it means that the code concentrates calculation effort on regions of interest without prior assumptions on the kernel shape. The code makes extensive use of redundancies in calculating kernels for different receivers or frequency-pass-bands for one earthquake, to facilitate its usage in large-scale global seismic tomography.

  15. Formation time and mean movement velocities of the 7 August Zhouqu debris flows extracted from broadband seismic records

    NASA Astrophysics Data System (ADS)

    Li, Z.; Huang, X.; Xu, Q.; Fan, J.; Yu, D.; Hao, Z.; Qiao, X.

    2015-01-01

    The catastrophic Zhouqu debris flows, which were induced by heavy rainfall, occurred at approximately midnight of 7 August 2010 (Beijing time, UTC + 8) and claimed 1765 lives. Broadband seismic signals recorded by the Zhouqu seismic station nearby are acquired and analyzed in this paper. The seismic signals are divided into two separate parts for the first time using the crucial time of 23:33:10 (Bejing time, UTC +8), with distinctly different frequency characteristics on time-by-time normalized spectrograms and amplitude increasing patterns on smoothed envelopes. They are considered to be generated by the development stage and the maturity stage of the Sanyanyu debris flow respectively. Seismic signals corresponding to the development stage have a broader main frequency band of approximately 0-15 Hz than that of the maturity stage, which is around 1-10 Hz. The N-S component can detect the development stage of the debris flow about 3 min earlier than other components due to its southward flow direction. Two sub-stages within the maturity stage are recognized from best-fitted amplitude increasing velocities and the satellite image of the Sanyanyu flow path and the mean movement velocities of the Sanyanyu debris flow during these two sub-stages are estimated to be 9.2 and 9.7 m s-1 respectively.

  16. Rationale for Seismic Measurements on Mars by a Single Station

    NASA Technical Reports Server (NTRS)

    Lognonne, P.; Banerdt, W. B.

    2003-01-01

    We present here some of the scientific objectives which can be achieved by a single seismic station on Mars, equipped with a 3 axis VBB seismometer and a 3 axis Short Period Seismometer. We assume that this station is also equipped with meteorological sensors, including infra-sound and pressure, in order to perform a complete meteorological noise correction. The science objectives are listed in order of increasing difficulty.

  17. Planning a Global Array of Broadband Seismic Arrays

    NASA Astrophysics Data System (ADS)

    Koper, Keith D.; Ammon, Charles J.

    2013-08-01

    A diverse group of more than 70 seismologists met for 2 days in Raleigh, N.C., to report on recent innovations in seismic array methods and to discuss the future of seismic arrays in global seismology. The workshop was sponsored by the Incorporated Research Institutions for Seismology (IRIS), with U.S. National Science Foundation funding. Participants included representatives of existing array research groups in Australia, Canada, Germany, Japan, Norway, and the United States, with individuals from academia, government, and industry. The workshop was organized by the authors of this meeting report, Pablo Ampeuro (California Institute of Technology), and Colleen Dalton (Boston University), along with IRIS staff support.

  18. Broadband analysis of landslides seismic signal : example of the Oso-Steelhead landslide and other recent events

    NASA Astrophysics Data System (ADS)

    Hibert, C.; Stark, C. P.; Ekstrom, G.

    2014-12-01

    Landslide failures on the scale of mountains are spectacular, dangerous, and spontaneous, making direct observations hard to obtain. Measurement of their dynamic properties during runout is a high research priority, but a logistical and technical challenge. Seismology has begun to help in several important ways. Taking advantage of broadband seismic stations, recent advances now allow: (i) the seismic detection and location of large landslides in near-real-time, even for events in very remote areas that may have remain undetected, such as the 2014 Mt La Perouse supraglacial failure in Alaska; (ii) inversion of long-period waves generated by large landslides to yield an estimate of the forces imparted by the bulk accelerating mass; (iii) inference of the landslide mass, its center-of-mass velocity over time, and its trajectory.Key questions persist, such as: What can the short-period seismic data tell us about the high-frequency impacts taking place within the granular flow and along its boundaries with the underlying bedrock? And how does this seismicity relate to the bulk acceleration of the landslide and the long-period seismicity generated by it?Our recent work on the joint analysis of short- and long-period seismic signals generated by past and recent events, such as the Bingham Canyon Mine and the Oso-Steelhead landslides, provides new insights to tackle these issues. Qualitative comparison between short-period signal features and kinematic parameters inferred from long-period surface wave inversion helps to refine interpretation of the source dynamics and to understand the different mechanisms for the origin of the short-period wave radiation. Our new results also suggest that quantitative relationships can be derived from this joint analysis, in particular between the short-period seismic signal envelope and the inferred momentum of the center-of-mass. In the future, these quantitative relationships may help to constrain and calibrate parameters used in

  19. Seismic noise study for a new seismic station at King Fahd University of Petroleum and Minerals in Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Kaka, S. I.

    2012-04-01

    We have carried out a seismic noise study in order to understand the noise level at three selected locations at King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia. The main purpose is to select a suitable site with low seismic noise and good signal-to-noise ratio for our new broadband seismic station. There are several factors involved in the selection of a site location for a new station. Most importantly, we need to strike a balance between a logistically convenient site versus a technically suitable site. As a starting point, we selected six potential sites due to accessibility and proximity to the seismic processing center laboratory in the Department of Earth Sciences (ESD) at KFUPM. We then eliminated two sites that are relatively close to possible low-frequency noise sources. We have considered many possible noise sources which include: vehicle traffic / heavy machinery, the direct path of air flowing from air conditioning vent, tall trees / power poles and metal doorways. One more site was eliminated because the site was located in the open where it experiences maximum wind speed which is considered a major source of noise. All three potential sites are situated within the Dammam Dome where both lower middle and upper Rus Formations are exposed. The upper Rus is mainly made up of fine grained chalky limestone and the lower Rus is made up of alternation of marls and thin dolomitic limestone. The area is not known for any major faults and considered very low seismicity and hence the identification of seismoteconic features is not required. Before conducting the noise study, we calibrated and tested the seismic recording system, which was recently acquired by the ESD at KFUPM. The system includes a seismic recorder and a sensor with a GPS device. We deployed the system in order to measure the low-frequency background noise. Knowing the low frequency noise will help in predicting the high-frequency noise. The recording systems were

  20. Extraction of Broadband Basin-Scale Green's Functions from the Ambient Seismic Field

    NASA Astrophysics Data System (ADS)

    Viens, L.; Koketsu, K.; Miyake, H.; Sakai, S.; Hirata, N.

    2015-12-01

    Many large cities in the world, including Tokyo and Los Angeles, are located atop sedimentary basins that have the potential to significantly amplify ground motions. The Kanto sedimentary basin, which underlies the Tokyo Metropolitan area, is filled by soft sediments and has a resonance period of 7-10 s, similar to the natural period of some tall buildings. To assess seismic hazard in this particularly seismically active area, we use the information carried by the ambient seismic field continuously recorded by more than 600 seismic stations that have been deployed in the basin. These stations equipped with three-component seismometers are a part of different networks, including the Metropolitan Seismic Observation network (MeSO-net), Hi-net and F-net of NIED, and the Japan Meteorological Agency (JMA) network. We extracted the 9 components of the Green's function tensors from the ambient seismic field using deconvolution for each pair of stations, regarding one as the virtual source and the other one as the receiver. We show that the extracted Green's functions contain body and surface waves having phase and amplification similar to the ones of earthquake records that occurred close to the virtual sources. For inter-station distances shorter than 30 km, time-frequency analyses suggest that Green's functions with energy higher than 1 Hz can be recovered. We use this dense array to investigate the effect of inter-station distance variations and azimuth dependences on the Green's function retrieval. Results show that the ambient seismic field recorded by stations situated at less than a few kilometers from each other can provide insights on seismic hazard assessment over a broad period range.

  1. Broadband Waveform Sensitivity Kernels for Large-Scale Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Nissen-Meyer, T.; Stähler, S. C.; van Driel, M.; Hosseini, K.; Auer, L.; Sigloch, K.

    2015-12-01

    Seismic sensitivity kernels, i.e. the basis for mapping misfit functionals to structural parameters in seismic inversions, have received much attention in recent years. Their computation has been conducted via ray-theory based approaches (Dahlen et al., 2000) or fully numerical solutions based on the adjoint-state formulation (e.g. Tromp et al., 2005). The core problem is the exuberant computational cost due to the large number of source-receiver pairs, each of which require solutions to the forward problem. This is exacerbated in the high-frequency regime where numerical solutions become prohibitively expensive. We present a methodology to compute accurate sensitivity kernels for global tomography across the observable seismic frequency band. These kernels rely on wavefield databases computed via AxiSEM (abstract ID# 77891, www.axisem.info), and thus on spherically symmetric models. As a consequence of this method's numerical efficiency even in high-frequency regimes, kernels can be computed in a time- and frequency-dependent manner, thus providing the full generic mapping from perturbed waveform to perturbed structure. Such waveform kernels can then be used for a variety of misfit functions, structural parameters and refiltered into bandpasses without recomputing any wavefields. A core component of the kernel method presented here is the mapping from numerical wavefields to inversion meshes. This is achieved by a Monte-Carlo approach, allowing for convergent and controllable accuracy on arbitrarily shaped tetrahedral and hexahedral meshes. We test and validate this accuracy by comparing to reference traveltimes, show the projection onto various locally adaptive inversion meshes and discuss computational efficiency for ongoing tomographic applications in the range of millions of observed body-wave data between periods of 2-30s.

  2. Preliminary results of receiver function analysis of seismic data recorded from a broadband deployment across the Gulf Coast Plain

    NASA Astrophysics Data System (ADS)

    Gurrola, H.; Pratt, K. W.; Pulliam, J.; Dunbar, J. A.

    2011-12-01

    In summer of 2010, 21 broadband seismographs were installed at 16-18 km spacing along a transect running from Johnson City, TX, (on the Edwards Plateau), to Matagorda Island to study the current structure of this rifted passive margin. The large magnetic anomaly that parallels the coast throughout the Gulf region moves on-shore beneath our transect such that we will be able to investigate the source of this anomaly. A second important target that will be imaged in this Balcones fault which is associated with the Ouachita front. This project is funded by a grant from the Norman Hackerman Advanced Research Program (NHARP), a biannual competition among Texas Universities to support research, and makes use of Texas Tech, Baylor, and UT Austin equipment. As a result, the deployment includes a less uniform array of seismic equipment, (10 Trillium compact seismometers and 10 Guralps; including 40Ts, 3Ts and 3ESPs), than projects supported by the IRIS PASSCAL center. Our vault construction was similar to Flexible array vaults, but Gulf Coast provides a more challenging environment for deployment than most encountered in the western US. The shallow water table and loose sediment can become almost fluid when storms deluge the area with rain. In dry periods, mud cracks near the vaults cause the vaults to tilt. As a result, even high quality, shallow seismic vaults can "float" or shift sufficiently to cause one or two components of the seismic stations to drift against their stops in days or weeks. As a result, the only data consistently available from all our stations, are vertical components. Horizontal component data from the summer of 2010 can be hit and miss due to the tilting of the vaults. These issues have been reduced in the summer of 2011 due to the drought. To address the data's shortcomings, we will average the vertical components from our stations and nearby EarthScope TA stations, (up 300 km away), to isolate the cleanest representation of the incoming P

  3. Estimating station noise thresholds for seismic magnitude bias elimination

    NASA Astrophysics Data System (ADS)

    Peacock, Sheila

    2014-05-01

    To eliminate the upward bias of seismic magnitude caused by censoring of signal hidden by noise, noise level at each station in a network must be estimated. Where noise levels are not measured directly, the method of Kelly and Lacoss (1969) has been used to infer them from bulletin data (Lilwall and Douglas 1984). To verify this estimate of noise level, noise thresholds of International Monitoring System (IMS) stations inferred from the International Data Centre (IDC) Reviewed Event Bulletin (REB) by the Kelly and Lacoss method for 2005-2013 are compared with direct measurements on (i) noise preceding first arrivals in filtered (0.8-4.5 Hz) IMS seismic data, and (ii) noise preceding the expected time of arrival of signals from events, where signal was not actually seen (values gathered by the IDC for maximum-likelihood magnitude calculation). For most stations the direct pre-signal noise measurements are ~0.25 units of log A/T lower than the Kelly&Lacoss thresholds; because the IDC automatic system declares a detection only when the short-term-average-to-long-term-average ratio threshold, which varies with station and frequency band between ~3-6, is exceeded. The noise values at expected times of non-observed signal arrival are ~0.15 units lower than the Kelly and Lacoss thresholds. Exceptions are caused by faulty channels being used for the direct noise or body-wave magnitude (mb) measurements or, for station ARCES and possibly FINES, SPITS and HFS, the wider filter used for signal amplitude than for signal detection admitting noise that swamped the signal. Abrupt changes in thresholds might show mis-documented sensor sensitivity changes at individual stations.

  4. Estimation of background noise level on seismic station using statistical analysis for improved analysis accuracy

    NASA Astrophysics Data System (ADS)

    Han, S. M.; Hahm, I.

    2015-12-01

    We evaluated the background noise level of seismic stations in order to collect the observation data of high quality and produce accurate seismic information. Determining of the background noise level was used PSD (Power Spectral Density) method by McNamara and Buland (2004) in this study. This method that used long-term data is influenced by not only innate electronic noise of sensor and a pulse wave resulting from stabilizing but also missing data and controlled by the specified frequency which is affected by the irregular signals without site characteristics. It is hard and inefficient to implement process that filters out the abnormal signal within the automated system. To solve these problems, we devised a method for extracting the data which normally distributed with 90 to 99% confidence intervals at each period. The availability of the method was verified using 62-seismic stations with broadband and short-period sensors operated by the KMA (Korea Meteorological Administration). Evaluation standards were NHNM (New High Noise Model) and NLNM (New Low Noise Model) published by the USGS (United States Geological Survey). It was designed based on the western United States. However, Korean Peninsula surrounded by the ocean on three sides has a complicated geological structure and a high population density. So, we re-designed an appropriate model in Korean peninsula by statistically combined result. The important feature is that secondary-microseism peak appeared at a higher frequency band. Acknowledgements: This research was carried out as a part of "Research for the Meteorological and Earthquake Observation Technology and Its Application" supported by the 2015 National Institute of Meteorological Research (NIMR) in the Korea Meteorological Administration.

  5. The ANSS Station Information System: A Centralized Station Metadata Repository for Populating, Managing and Distributing Seismic Station Metadata

    NASA Astrophysics Data System (ADS)

    Thomas, V. I.; Yu, E.; Acharya, P.; Jaramillo, J.; Chowdhury, F.

    2015-12-01

    Maintaining and archiving accurate site metadata is critical for seismic network operations. The Advanced National Seismic System (ANSS) Station Information System (SIS) is a repository of seismic network field equipment, equipment response, and other site information. Currently, there are 187 different sensor models and 114 data-logger models in SIS. SIS has a web-based user interface that allows network operators to enter information about seismic equipment and assign response parameters to it. It allows users to log entries for sites, equipment, and data streams. Users can also track when equipment is installed, updated, and/or removed from sites. When seismic equipment configurations change for a site, SIS computes the overall gain of a data channel by combining the response parameters of the underlying hardware components. Users can then distribute this metadata in standardized formats such as FDSN StationXML or dataless SEED. One powerful advantage of SIS is that existing data in the repository can be leveraged: e.g., new instruments can be assigned response parameters from the Incorporated Research Institutions for Seismology (IRIS) Nominal Response Library (NRL), or from a similar instrument already in the inventory, thereby reducing the amount of time needed to determine parameters when new equipment (or models) are introduced into a network. SIS is also useful for managing field equipment that does not produce seismic data (eg power systems, telemetry devices or GPS receivers) and gives the network operator a comprehensive view of site field work. SIS allows users to generate field logs to document activities and inventory at sites. Thus, operators can also use SIS reporting capabilities to improve planning and maintenance of the network. Queries such as how many sensors of a certain model are installed or what pieces of equipment have active problem reports are just a few examples of the type of information that is available to SIS users.

  6. Broadband seismic measurements of degassing activity associated with lava effusion at Popocatépetl Volcano, Mexico

    USGS Publications Warehouse

    Arciniega-Ceballos, Alejandra; Chouet, Bernard A.; Dawson, Phillip; Asch, Guenter

    2008-01-01

    From November 1999 through July 2000, a broadband seismic experiment was carried out at Popocatépetl Volcano to record seismic activity over a wide period range (0.04–100 s). We present an overview of the seismicity recorded during this experiment and discuss results of analyses of long-period (LP) and very-long-period (VLP) seismic signals recorded at stations nearest to the crater over a four-month interval December 1999–March 2000. Three families of LP signals (Types-I, II, and III) are identified based on distinctive waveform features observed periods shorter than 1 s, periods longer than 15 s, and within the period range 0.5–2.5 s. Type-I LP events have impulsive first arrivals and exhibit a characteristic harmonic wave train with dominant periods in the 1.4–1.9 s range during the first 10 s of signal. These events are also associated with a remarkable VLP wavelet with period near 30 s. Type-II LP events represent pairs of events occurring in rapid succession and whose signatures are superimposed. These are typically marked by slowly emergent first arrivals and by a characteristic VLP wave train with dominant period near 30 s, made of two successive wavelets whose shapes are quasi-identical to those of the VLP wavelets associated with Type-I events. Type-III LP events represent the most energetic signals observed during our experiment. These have an emergent first arrival and display a harmonic signature with dominant period near 1.1 s. They are dominated by periods in the 0.25–0.35 s band and contain no significant energy at periods longer than 15 s. Hypocentral locations of the three types of LP events obtained from phase picks point to shallow seismic sources clustered at depths shallower than 2 km below the crater floor. Observed variations in volcanic eruptive activity correlate with defined LP families. Most of the observed seismicity consists of Type-I events that occur in association with 1–3-min-long degassing bursts (

  7. Potential improvements in horizontal very broadband seismic data in the IRIS/USGS component of the Global Seismic Network

    USGS Publications Warehouse

    Ringler, Adam; Steim, J.M.; Zandt, T; Hutt, Charles R.; Wilson, David; Storm, Tyler

    2016-01-01

    The Streckeisen STS‐1 has been the primary vault‐type seismometer used in the over‐150‐station Global Seismographic Network (GSN). This sensor has long been known for its outstanding vertical, very long‐period (e.g., >100  s period), and low‐noise performance, although the horizontal long‐period noise performance is less well known. The STS‐1 is a limited, important resource, because it is no longer made or supported by the original manufacturer. We investigate the incoherent noise of horizontal‐component sensors, where coherent signals among sensors have been removed, giving an upper bound on the self‐noise of both the STS‐1 and STS‐2 horizontal components. Our findings suggest that a well‐installed STS‐2 could potentially produce data with similar or better incoherent noise levels to that of a horizontal‐component STS‐1. Along with our experimental investigation, we compare background noise levels for a calendar year at Incorporated Research Institutions for Seismology/U.S. Geological Survey network stations, which comprise approximately two‐thirds of the GSN, with collocated STS‐1 and STS‐2 seismometers. The use of an STS‐2‐class of sensor (flat to velocity to 120 s period) to acquire low‐frequency data in surface‐vault installations would allow network operators to focus more attention on improving vertical data. In order to deal with the difference in instrument response shapes between the two instruments, we detail two different time‐domain filters that would allow users to convert broadband STS‐2 data into very broadband data with a response similar to that of an STS‐1 (flat to velocity to 360 s period). We conclude that the complexity of the current primary horizontal vault sensors in the GSN may not be necessary until we are better able to isolate surface horizontal sensors from various noise sources.

  8. A new dataset of Wood Anderson magnitude from the Trieste (Italy) seismic station

    NASA Astrophysics Data System (ADS)

    Sandron, Denis; Gentile, G. Francesco; Gentili, Stefania; Rebez, Alessandro; Santulin, Marco; Slejko, Dario

    2014-05-01

    The standard torsion Wood Anderson (WA) seismograph owes its fame to the fact that historically it has been used for the definition of the magnitude of an earthquake (Richter, 1935). With the progress of the technology, digital broadband (BB) seismographs replaced it. However, for historical consistency and homogeneity with the old seismic catalogues, it is still important continuing to compute the so called Wood Anderson magnitude. In order to evaluate WA magnitude, the synthetic seismograms WA equivalent are simulated convolving the waveforms recorded by a BB instrument with a suitable transfer function. The value of static magnification that should be applied in order to simulate correctly the WA instrument is debated. The original WA instrument in Trieste operated from 1971 to 1992 and the WA magnitude (MAW) estimates were regularly reported in the seismic station bulletins. The calculation of the local magnitude was performed following the Richter's formula (Richter, 1935), using the table of corrections factor unmodified from those calibrated for California and without station correction applied (Finetti, 1972). However, the WA amplitudes were computed as vector sum rather than arithmetic average of the horizontal components, resulting in a systematic overestimation of approximately 0.25, depending on the azimuth. In this work, we have retrieved the E-W and N-S components of the original recordings and re-computed MAW according to the original Richter (1935) formula. In 1992, the WA recording were stopped, due to the long time required for the daily development of the photographic paper, the costs of the photographic paper and the progress of the technology. After a decade of interruption, the WA was recovered and modernized by replacing the recording on photographic paper with an electronic device and it continues presently to record earthquakes. The E-W and N-S components records were memorized, but not published till now. Since 2004, next to the WA (few

  9. Real-time detection, location, and characterization of rockslides using broadband regional seismic networks

    NASA Astrophysics Data System (ADS)

    Manconi, Andrea; Picozzi, Matteo; Coviello, Velio; De Santis, Francesca; Elia, Luca

    2016-07-01

    We propose a new real-time approach to detect, locate, and estimate the volume of rockslides by analyzing waveforms acquired from broadband regional seismic networks. The identification of signals generated by rockslides from other sources, such as natural and/or induced earthquakes, is accomplished by exploiting the ratio between local magnitudes (ML) and duration magnitudes (MD). We found that signals associated with rockslides have ML/MD < 0.8, while for earthquakes ML/MD ≅ 1. In addition, we derived an empirical relationship between MD and rockslide volumes, obtaining a preliminary characterization of rockslide volume within seconds after their occurrence. The key points of this study are presented by testing the hypothesis on a recent rockslide event that occurred in northern Italy. We discuss also the potential evolution of the methodology for early warning and/or rapid response purposes.

  10. One-Station Seismology Without Traditional Seismic Sources (Invited)

    NASA Astrophysics Data System (ADS)

    Tsai, V. C.

    2010-12-01

    Information about the interior of planetary bodies other than the Earth is difficult to obtain. While seismology has been extremely successful on the Earth, there has been a reluctance to use precious payload weight to send a single seismometer aboard a lander. Much of this reluctance focuses on the idea that a single seismometer could not provide useful information about the subsurface. However, this notion relies on old concepts of seismology in which large earthquakes recorded at many stations are a prerequisite for obtaining useful data, whereas a number of new techniques (e.g. cross correlation, deconvolution and spectral analysis applied to noise) have shown that non-traditional sources of seismic waves can potentially be very useful. Furthermore, some of these techniques can be applied to data from a single station. Here, we therefore challenge the old notion of the prerequisites for seismology by demonstrating how a single seismometer that is well-coupled to the ground can potentially deliver useful information about the shallow subsurface and crustal structure (including the presence or absence of liquids there), and even possibly average global structure. The success of these measurements depends on a number of factors, including the type of seismic sources that are available, the temporal variability of these sources, the length of time that the station reports data, and certain properties of the subsurface. After making some order-of-magnitude estimates regarding these parameters, we make a quantitative assessment of what would need to be achieved technologically in order for the measurements to succeed. While this assessment is planet-dependent, our first order conclusions are that shallow reflectors could potentially be imaged with current technology, that crustal reverberations could be analyzed if there exists relatively strong surface activity (e.g. volcanism, large rivers, ice tectonics or active sources), but that deeper structure may be

  11. Broadband Seismic Analyses of the Crust and Noise Sources in Alberta, Canada

    NASA Astrophysics Data System (ADS)

    Shen, Luyi

    Cross-correlation of continuous seismic recordings has been proven effective in extracting the Green's function between two seismic stations. Travel-time and waveform source migration calculations jointly suggest a persistent noise source near Lesser Slave Lake (LSL), a large ice-covered lake in Alberta, Canada, during winter months. Subspace inversions of effective Green's functions from five narrow frequency bands (0.002-0.2 Hz) reveal low velocities in the upper crust beneath Alberta basin, which indicates strong effects from the thick platform sedimentary cover. Consistently low velocities are also observed beneath Wabamun domain but the areal coverage is considerably smaller than the published domain boundaries. The lower-crustal velocities beneath southern Loverna Block is 10% faster than the regional average. As the possible remnant cratonic core of the Hearne province, this northeast-striking anomaly extends to the western part of Medicine Hat Block and contributes to a strong east-west structural gradient in the latter domain.

  12. An Application of the Coda Methodology for Moment-Rate Spectra Using Broadband Stations in Turkey

    SciTech Connect

    Eken Tuna, Kevin Mayeda, Abraham Hofstetter, Rengin Gok, Gonca Orgulu, Niyazi Turkelli

    2004-07-11

    A recently developed coda magnitude methodology was applied to selected broadband stations in Turkey for the purpose of testing the coda method in a large, laterally complex region. As found in other, albeit smaller regions, coda envelope amplitude measurements are significantly less variable than distance-corrected direct wave measurements (i.e., L{sub g} and surface waves) by roughly a factor 3-to-4. Despite strong lateral crustal heterogeneity in Turkey, they found that the region could be adequately modeled assuming a simple 1-D, radially symmetric path correction. After calibrating the stations ISP, ISKB and MALT for local and regional distances, single-station moment-magnitude estimates (M{sub W}) derived from the coda spectra were in excellent agreement with those determined from multistation waveform modeling inversions, exhibiting a data standard deviation of 0.17. Though the calibration was validated using large events, the results of the calibration will extend M{sub W} estimates to significantly smaller events which could not otherwise be waveform modeled. The successful application of the method is remarkable considering the significant lateral complexity in Turkey and the simple assumptions used in the coda method.

  13. Microseismic Monitoring Using Surface and Borehole Seismic Stations in an Oil Field, North Oman

    NASA Astrophysics Data System (ADS)

    El-Hussain, I.; Al-Hashmi, S.; Al-Shijbi, Y.; Al-Saifi, M.; Al-Toubi, K.; Al-Lazki, A.; Al-Kindy, F.

    2009-05-01

    Five shallow borehole seismic stations were installed to monitor microearthquake activities in a carbonate oil field in northern Oman since 1999. This shallow network of seismic station operated continuously until 2002 after which intermittent seismic recording took place due to lack of maintenance and failure of some stations. The objectives of the study are to determine the microseismic parameters in the oil field and to determine the spatial and temporal distribution of these events to evaluate possible triggering mechanism. Well over 400 microearthquakes per year were recorded in the first three years of operation and after that the level of seismic recording fell to less than 200 microearthquakes per year due to failure of some stations. In March 2008, temporary seismic experiment consisting of five near surface seismic stations were installed in the oil field to augment the shallow network station and to evaluate surface installment of seismic instrument to monitor microseismic activities. It has been recognized that microearthquakes data such as size, spatial, and temporal distribution provide information on the pressure waves initiated by either production of or injection of fluids into reservoirs. A total of 44 local microearthquake events were analyzed and located during the temporary seismic stations deployment using a non-linear location software that allows the use of variable accurate velocity model of the subsurface. The events location is confined to oil field reservoir boundary during the recording period and more events occurring at shallow depth. The correlation coefficient between gas production and number of events is the higher compared with the oil production or water injection. The focal plane solution for the largest event in the sequence indicates normal faulting with extensional stress consistent with the existing mapped normal faults in the oil field. Microseismic signal clearly detected by the collocated sensors of the near surface

  14. NX-2G : autonomous BBOBS-NX for a highly mobile broadband seismic observation at the seafloor

    NASA Astrophysics Data System (ADS)

    Shiobara, Hajime; Sugioka, Hiroko; Ito, Aki; Shinohara, Masanao

    2016-04-01

    We had developed the broadband ocean bottom seismometer (BBOBS) and its new generation system (BBOBS-NX), and, with them, several practical observations have been performed to create and establish a new category of the ocean floor broadband seismology, since 1999. Now, our BBOBS and BBOBS-NX data is proved to be at acceptable level for broadband seismic analyses. Especially, the BBOBS-NX is able to obtain the low noise horizontal data comparable to the land station in periods longer than 10 s, which is adequate for modern analyses of the mantle structure. Moreover, the BBOBS(T)-NX is under practical evaluation for the mobile tilt observation at the seafloor, which will enable dense geodetic monitoring. The BBOBS-NX system must be a powerful tool, although, the current system has intrinsic limitation in opportunity of observations due to the necessary use of the submersible vehicle for the deployment and recovery. If we can use this system with almost any kind of vessels, like as the BBOBS (self pop-up system), it should lead us a true breakthrough of seafloor observations in geodynamics. Hereafter, we call the new autonomous BBOBS-NX as NX-2G in short. There are two main problems to be cleared to realize the NX-2G system. The first one is a tilt of the sensor unit on landing, which is larger than the acceptable limit of the sensor (±8°) in 47 % after our 15 free-fall deployments of the BBOBS-NX. As we had no evidence at which moment the tilt occurred, so it was observed during the BBOBS-NX deployment in the last year by attaching a video camera and an acceleration logger those were originally developed for this purpose. The only one result shows that the tilt on landing seemed determined by the final posture of the BBOBS-NX system just before the penetration into the sediment. The second problem is a required force to extract the sensor unit from the sticky clay sediment, which was about 80 kgf in maximum with the current BBOBS-NX system from in-situ measurements

  15. Dynamics of the Oso-Steelhead landslide from broadband seismic analysis

    NASA Astrophysics Data System (ADS)

    Hibert, C.; Stark, C. P.; Ekström, G.

    2015-06-01

    We carry out a combined analysis of the short- and long-period seismic signals generated by the devastating Oso-Steelhead landslide that occurred on 22 March 2014. The seismic records show that the Oso-Steelhead landslide was not a single slope failure, but a succession of multiple failures distinguished by two major collapses that occurred approximately 3 min apart. The first generated long-period surface waves that were recorded at several proximal stations. We invert these long-period signals for the forces acting at the source, and obtain estimates of the first failure runout and kinematics, as well as its mass after calibration against the mass-centre displacement estimated from remote-sensing imagery. Short-period analysis of both events suggests that the source dynamics of the second event is more complex than the first. No distinct long-period surface waves were recorded for the second failure, which prevents inversion for its source parameters. However, by comparing the seismic energy of the short-period waves generated by both events we are able to estimate the volume of the second. Our analysis suggests that the volume of the second failure is about 15-30% of the total landslide volume, giving a total volume mobilized by the two events between 7 × 106 and 10 × 106 m3, in agreement with estimates from ground observations and lidar mapping.

  16. Complex force history of a calving-generated glacial earthquake derived from broadband seismic inversion

    NASA Astrophysics Data System (ADS)

    Sergeant, Amandine; Mangeney, Anne; Stutzmann, Eléonore; Montagner, Jean-Paul; Walter, Fabian; Moretti, Laurent; Castelnau, Olivier

    2016-02-01

    The force applied to the Earth by the calving of two icebergs at Jakobshavn Isbrae, Greenland, has been quantified. The source force history was recovered by inversion of regional broadband seismograms without any a priori constraint on the source time function, in contrast with previous studies. For periods 10-100 s, the three-component force can be obtained from distant stations alone and is proportional to the closest station seismograms. This inversion makes it possible to quantify changes of the source force direction and amplitude as a function of time and frequency. A detailed comparison with a video of the event was used to identify four forces associated with collision, then bottom-out and top-out rotation of the first and second icebergs, and ice mélange motion. Only the two iceberg rotations were identified in previous studies. All four processes are found here to contribute to the force amplitude and variability. Such a complete time-frequency force history provides unique dynamical constraints for mechanical calving models.

  17. Seismotectonic study of Kishtwar region of Jammu Province using local broadband seismic data

    NASA Astrophysics Data System (ADS)

    Pandey, Shiv Jyoti; Bhat, G. M.; Puri, Shveta; Raina, Neha; Singh, Yudhbir; Pandita, S. K.; Verma, Mithila; Bansal, B. K.; Sutar, Anup

    2016-10-01

    Two moderate earthquakes of Mw 5.7 on the first of May and Mw 5.2 on the second of August occurred in the Kishtwar region in the year 2013. Our broadband seismic observatories located in the region recorded these events and the aftershocks. We analyzed these data to understand the seismotectonics of this region. Most of the events were located between 33.03° to 33.29° N latitude and 75.40° to 76.07° E longitude. Focal depths of these shallow earthquakes range from 7 to 12 km and are confined between Panjal Thrust (PT) and Kishtwar Window (KW). Spectral analysis of these events reveals that stress drop, source radius, corner frequency, and moment magnitude varied between 3.3 and 70.1 bars, 0.121 and 3.55 km, 0.397 and 6.06 Hz, and Mw 2.2 and Mw 5.7, respectively. The low stress drop of small-magnitude earthquakes reveals the brittle nature of the upper crust which is coincident with the field observations. The variation of stress drop with magnitude shows positive correlation whereas no such relation was observed between stress drop and depth of focus. The b value calculated (0.83) for the area reveals high stress accumulation within the incompetent rock zones in the area.

  18. Seismic margin review of the Maine Yankee Atomic Power Station: Fragility analysis

    SciTech Connect

    Ravindra, M. K.; Hardy, G. S.; Hashimoto, P. S.; Griffin, M. J.

    1987-03-01

    This Fragility Analysis is the third of three volumes for the Seismic Margin Review of the Maine Yankee Atomic Power Station. Volume 1 is the Summary Report of the first trial seismic margin review. Volume 2, Systems Analysis, documents the results of the systems screening for the review. The three volumes are part of the Seismic Margins Program initiated in 1984 by the Nuclear Regulatory Commission (NRC) to quantify seismic margins at nuclear power plants. The overall objectives of the trial review are to assess the seismic margins of a particular pressurized water reactor, and to test the adequacy of this review approach, quantification techniques, and guidelines for performing the review. Results from the trial review will be used to revise the seismic margin methodology and guidelines so that the NRC and industry can readily apply them to assess the inherent quantitative seismic capacity of nuclear power plants.

  19. Broadband Sound Pressure Field Characteristics of Marine Seismic Sources Used by R/V Polarstern

    NASA Astrophysics Data System (ADS)

    Breitzke, M.; Boebel, O.; El Naggar, S.; Jokat, W.; Kuhn, G.; Niessen, F.; Schenke, H.; Werner, B.; Diebold, J.

    2006-05-01

    Single airguns and airgun arrays of different size and volume are used as sound sources for scientific marine seismic reflection and refraction surveys conducted by R/V Polarstern in the Arctic and Antarctic Ocean. To ensure that these research activities do not affect marine wildlife and particularly marine mammals in the Antarctic Treaty Area south of 60°S knowledge of the sound pressure field of the seismic sources is essential. Therefore, a broadband marine seismic source characterization study was conducted at the Heggernes Acoustic Range in the Herdlefjord, Norway in October 2003. The objectives were (1) to determine the spatial distribution of the sound pressure levels emitted by Polarstern's seismic sources, (2) to compute the source levels assuming a spherical amplitude decay, (3) to determine mitigation radii, within which at least some species of marine mammals might possibly experience behavioral or physiological disturbance due to the received sound pressure levels. The thresholds currently in use to determine mitigation radii are 160 dBRMS re 1 μPa for potential behavioral disturbance and 180 dBRMS re 1 μPa for potential physiological and hearing effects like temporary threshold shifts. To determine the spatial distribution of the sound pressure levels each airgun (array) was shot along a line of 2- 3 km length running between 2 hydrophone chains with receivers in 35, 100, 198 and 267 m depth. A GI-Gun (2.4 l), a G-Gun (8.5 l) and a Bolt PAR CT800 (32.8 l) were deployed as single sources, and 3 GI-Guns (7.4 l), 3 G-Guns (25.6 l) and 8 VLF-Guns (24 l) as arrays. The measurements are complemented by a modeling approach for an 8 G-Gun (68.2 l) and 8 G-Gun+1 Bolt PAR CT800 array (100.1 l). The data analysis includes a determination of peak-peak, zero-peak and RMS-amplitudes, sound exposure levels and amplitude spectra as function of source-receiver distance. The amplitude vs distance graphs, analyzed for the 4 hydrophone depths, show the typical

  20. A broadband multicomponent seismic landstreamer for underground infrastructure planning projects - An example from the Varberg tunnel, southwest Sweden

    NASA Astrophysics Data System (ADS)

    Malehmir, Alireza; Zhang, Fengjiao; Lundberg, Emil; Dehgahnnejad, Mahdieh; Friberg, Olof; Brodic, Bojan; Dose, Christin; Place, Joachim; Svensson, Mats; Moller, Henrik

    2015-04-01

    Over the past few years, demand for infrastructures has continuously increased in Sweden. The authorities are expected to invest significantly on infrastructures especially those that are environmentally friendly and aim at reducing CO2 emission. Due to limited surface accessibility, the country will particularly move towards developing more and more subways, train tunnels, underground highways and bypasses. The focus will then obviously be in major cities where the underground infrastructures have to be constantly developed or expanded to facilitate the daily life and transportation. The degree to which we can understand geological conditions where these structures are going to be constructed also has great economical and environmental effects. What, however, makes urban environment challenging target for geophysical investigations is the various sources of noise and restriction both in time and space, which require the equipment to be versatile and to produce minimal disruption as well as fast to set up and pack. As a part of a nation-wide, an academia-industry partnership, project (TRUST, TRansparent Underground STructure), we have developed a multicomponent broadband digital-based sensor seismic landstreamer system that is particularly geared for noisy environments and areas where high-resolution images of the subsurface are needed. The streamer has been tested for its reliability in various locations (e.g., part of the Stockholm Bypass) and for various targets one which was a planned underground train tunnel in the city of Varberg, southwest Sweden that is the focus of this presentation. Potential targets were bedrock surface, fracture zones, weak and shear zones. During nearly three weeks, totally about 7.5 km long, comprising 25 seismic profiles using a source and receiver spacing of 2-4 m, was acquired. A novel approach in the data acquisition was to combine the landstreamer with wireless sensors in areas where accessibility was restricted and, to provide

  1. Seismic Station Installation Orientation Errors at ANSS and IRIS/USGS Stations

    USGS Publications Warehouse

    Ringler, Adam T.; Hutt, Charles R.; Persfield, K.; Gee, Lind S.

    2013-01-01

    Many seismological studies depend on the published orientations of sensitive axes of seismic instruments relative to north (e.g., Li et al., 2011). For example, studies of the anisotropic structure of the Earth’s mantle through SKS‐splitting measurements (Long et al., 2009), constraints on core–mantle electromagnetic coupling from torsional normal‐mode measurements (Dumberry and Mound, 2008), and models of three‐dimensional (3D) velocity variations from surface waves (Ekström et al., 1997) rely on accurate sensor orientation. Unfortunately, numerous results indicate that this critical parameter is often subject to significant error (Laske, 1995; Laske and Masters, 1996; Yoshizawa et al., 1999; Schulte‐Pelkum et al., 2001; Larson and Ekström, 2002). For the Advanced National Seismic System (ANSS; ANSS Technical Integration Committee, 2002), the Global Seismographic Network (GSN; Butler et al., 2004), and many other networks, sensor orientation is typically determined by a field engineer during installation. Successful emplacement of a seismic instrument requires identifying true north, transferring a reference line, and measuring the orientation of the instrument relative to the reference line. Such an exercise is simple in theory, but there are many complications in practice. There are four commonly used methods for determining true north at the ANSS and GSN stations operated by the USGS Albuquerque Seismological Laboratory (ASL), including gyroscopic, astronomical, Global Positioning System (GPS), and magnetic field techniques. A particular method is selected based on site conditions (above ground, below ground, availability of astronomical observations, and so on) and in the case of gyroscopic methods, export restrictions. Once a north line has been determined, it must be translated to the sensor location. For installations in mines or deep vaults, this step can include tracking angles through the one or more turns in the access tunnel leading to

  2. Mikhnevo: from seismic station no. 1 to a modern geophysical observatory

    NASA Astrophysics Data System (ADS)

    Adushkin, V. V.; Ovchinnikov, V. M.; Sanina, I. A.; Riznichenko, O. Yu.

    2016-01-01

    The Mikhnevo seismic station was founded in accordance with directive no. 1134 RS of the Council of Ministers of the Soviet Union of February 6, 1954. The station, installed south of Moscow, began its operations on monitoring nuclear tests in the United States and England in 1954. For dozens of years this station was the leading experimental base for elaborating new technical solutions and methods for monitoring nuclear explosions, equipped with modern seismological instruments. At present, the focus of activities has been moved from military applications to fundamental geophysical research. The station preserves its leading position in seismological observations due to the development of national high-performance digital instruments and creation of the small-aperture seismic array, the only one in the central part of European Russia, which is capable of recording weak seismic events with M L ≥ 1.5 within a distance of 100 km.

  3. Broadband Seismic Observations of Lone Star Geyser, Yellowstone National Park, Wyoming, USA

    NASA Astrophysics Data System (ADS)

    Nayak, A.; Hurwitz, S.; Johnson, H. E., III; Manga, M.; Gomez, F. G.

    2014-12-01

    Geysers are natural phenomena that episodically erupt water and steam. Geophysical observations at geysers are analyzed to shed light on subsurface multi-phase mass and heat exchange processes and geometries controlling geyser eruptions, which are still are not completely understood. Lone Star Geyser (LSG) in Yellowstone National Park, Wyoming, USA erupts every ~3 hours, with brief episodes (~5-10 min) of water and steam fountaining (preplays) leading up to the main eruption (~28 min), and the discharge evolves from a water-dominated phase to a steam-dominated phase as the main eruption proceeds in time. We describe observations from multiple seismometers deployed around LSG as part of a comprehensive geophysical survey conducted in April 2014. 3-component seismograms were continuously recorded at 250 samples per second by 6 Nanometrics Trillium 120 P/PA broadband seismometers (lower corner frequency at 120 seconds) and Taurus dataloggers at distances ~10 to 25 m from the geyser cone for a period of 3 days. We identify distinct episodes of hydrothermal tremor associated with preplay events and main eruptions. We find that the dominant tremor frequencies during main eruptions are consistently higher (> 10.0 Hz) than those during preplays (> 1.0 Hz) indicating slightly different source locations or processes controlling the two phenomena. Unlike seismic observations at the Old Faithful Geyser, we also observe subtle harmonic tremor and spectral gliding in the frequency range ~1.0-8.0 Hz towards the end of both main eruption and preplay tremor episodes. We interpret long-period pulses on horizontal components of the seismometers located close to the geyser and synchronous with preplays, as pseudo-tilts resulting from deformation of the sinter terrace. We also compare the evolution of hydrothermal tremor in time with synchronous changes in temperature, acoustic emission and discharge for interpretation of the possible tremor source processes.

  4. Performance of an island seismic station for recording T-phases

    SciTech Connect

    Hanson, J. A., LLNL

    1998-05-01

    As part of the International Monitoring System (IMS) a worldwide hydroacoustic network consisting of 6 hydrophone and 5 island seismic stations has been planned which will monitor for underwater or low altitude atmospheric explosions. Data from this network is to be integrated with other IMS networks monitoring the Comprehensive Nuclear Test-Ban Treaty. The seismic (T-phase) stations are significantly less sensitive than hydrophones to ocean borne acoustic waves. T-phase signal strength at seismic stations depends on the amplitude of the signal in the water column, the hydroacoustic-seismic conversion efficiency, and loss on the seismic portion of the path through the island. In order to understand how these factors influence the performance of T-phase stations seismic and hydroacoustic data are examined from instruments currently deployed on or around Ascension Island in the South Atlantic Ocean. T-phase recordings for the last 3 years have been collected from the GSN seismic station ASCN on Ascension Island. Surrounding the island are 5 hydrophones which are part of the U.S. Air Force Missile Impact Locating System (MILS). Data from this system have been obtained for some of the events observed at ASCN. Four of the hydrophones are located within 30 km of the coast while the fifth instrument is 100 km to the south. Amplitude spectral estimates of the signal-to-noise levels (SNL) are computed and generally peak between 3 and 8 Hz for both the seismometer and hydrophone data. The seismic SNL generally decays to 1 between 10 and 15 Hz while the hydrophone SNL is still large well above 20 Hz. The ratios of the hydrophone-to-seismometer SNL, at their peak in energy, range between 10 and 100 (20-40 dB) unless a hydrophone is partially blocked by the Ascension Island landmass.

  5. Estimating Seismic Moment From Broadband P-Waves for Tsunami Warnings.

    NASA Astrophysics Data System (ADS)

    Hirshorn, B. F.

    2006-12-01

    The Richard H. Hagemeyer Pacific Tsunami Warning Center (PTWC), located in Ewa Beach, Oahu, Hawaii, is responsible for issuing local, regional, and distant tsunami warnings to Hawaii, and for issuing regional and distant tsunami warnings to the rest of the Pacific Basin, exclusive of the US West Coast. The PTWC must provide these tsunami warnings as soon as technologically possible, based entirely on estimates of a potentially tsunamigenic earthquake's source parameters. We calculate the broadband P-wave moment magnitude, Mwp, from the P or pP wave velocity seismograms [Tsuboi et al., 1995, 1999]. This method appears to work well for regional and teleseismic events [ Tsuboi et al (1999], Whitmore et al (2002), Hirshorn et al (2004) ]. Following Tsuboi, [1995], we consider the displacement record of the P-wave portion of the broadband seismograms as an approximate source time function and integrate this record to obtain the moment rate function, Mo(t), and the moment magnitude [Hanks and Kanamori, 1972] as a function of time, Mw(t). We present results for Mwp for local, regional, and teleseismic broad band recordings for earthquakes in the Mw 5 to 9.3 range. As large Hawaii events are rare, we tested this local case using other Pacific events in the magnitude 5.0 to 7.5 range recorded by nearby stations. Signals were excluded, however, if the epicentral distance was so small (generally less than 1 degree) that there was contamination by the S-wave too closely following the P-waves. Scatter plots of Mwp against the Harvard Mw for these events shows that Mwp does predict Mw well from seismograms recorded at local, regional, and teleseismic distances. For some complex earthquakes, eg. the Mw 8.4(HRV) Peru earthquake of June 21, 2001, Mwp underestimates Mw if the first moment release is not the largest. Our estimates of Mwp for the Mw 9.3 Summatra-Andaman Island's earthquake of December 26, 2004 and for the Mw 8.7 (HRV) Summatra event of March 28, 2005, were Mwp 8

  6. Using Seismic Signals as a Quality Assessment Tool of USArray stations at the Array Network Facility

    NASA Astrophysics Data System (ADS)

    Astiz, L.; Eakins, J. A.; Martynov, V. G.; Vernon, F. L.; Newman, R. L.; Reyes, J. C.; Cox, T. A.; Karasu, G. H.

    2009-12-01

    Full deployment of the 400 Transportable Array (TA) stations of the USArray Earthscope project was reached in September 2007. The original array footprint has rolled eastward at a rate of 200 stations per year. The Array Network Facility (ANF) is responsible for the delivery of all TA data (seismic, state of health and metadata) to the IRIS Data Management Center (DMC). In addition, the ANF provides station command and control; verification and distribution of metadata; remotely accessible world wide web interfaces for Array Operations Facility (AOF) personnel to access network and station state of health information; and quality control for all seismic data. ANF seismic analysts review individual seismic events recorded by the USArray, and to-date have produced over 2.5 million arrival picks from more than 40,000 local, regional and teleseismic events since April 2004. In the last two years, as the TA has moved away from the seismically active west coast of the United States, most of the local and regional events recorded are man-made events. The arrival picks are available in IMS format at the DMC and as compressed CSS3.0 relational databases from the ANF website. The eyes-on-data approach of these seismic signals by ANF analysts in quasi-real time allows for data quality monitoring of all deployed TA stations. This approach also allows the ANF to quickly discover problems at the stations as the network evolves given that the USArray currently records about 25 seismic events per day and that large teleseismic earthquakes (M > 6.5) are recorded at nearly all USArray stations. We use an empirical approach to compare body and surface wave recordings at a particular station with the robust stack of the nearest neighbors’ recordings to monitor continuing station performance. Using this empirical approach we will compare particle motion of P and S waves of the largest 30 shallow & deep earthquakes recorded by USArrray stations to verify sensor orientation. We will

  7. The "Jerk" Method for Predicting Intrusions and Eruptions of Piton De La Fournaise (La Réunion Island) from the Analysis of the Broadband Seismological Rer Station

    NASA Astrophysics Data System (ADS)

    Roult, G. C.; Beauducel, F.; Ferrazzini, V.; Boissier, P.; Villeneuve, N.

    2014-12-01

    The predictability of volcanic eruptions remains a challenging problem and forecast of volcano behavior (intrusion versus eruption) is a difficult task. Since 1979, the Volcano Observatory of Piton de la Fournaise (OVPF) maintains SP and BB seismic stations, tiltmeters, extensometers and GPS stations. In addition, the RER GEOSCOPE broadband station was installed in 1986, 8.5 km north of the summit crater. The analysis of 83 seismic crises from December 1985 to December 2010 (preceding 54 eruptions, 26 intrusions, 2 summit pit craters,1 caldera collapse) allowed us to identify short-term long period seismic transients (period > 100 s) for most events (Roult et al., 2012). These precursors observed on the horizontal components are tilt signals induced by the inflation/deflation of the volcano. We analyzed 17 eruptions and 7 intrusions spanning the 2005-2010 period with the aim of distinguishing whether an injection of magma will stop or if it can evolve towards an eruption. Transient signature is an acceleration step that can be large or not, with slopes more or less steep according to the acceleration rate. We show a clear differentiation between the acceleration rate of the intrusions (low rate) and the acceleration rate of the eruptions (high rate). With a ratio estimated to 7, the acceleration rate allows to determine a threshold value and to discriminate between intrusive and eruptive events. The real-time calculation of the ground acceleration of the horizontal components of the RER station after removal of the theoretical tide effect is integrated since April 2014 to the Piton de la Fournaise volcano monitoring. In June 2014, the "JERK"method predicted an eruption 50 minutes before the eruption onset. We applied the "material failure prediction" of Voight and Cornelius (1991) with the aim to predict the onset time of the eruptions. Preliminary tests on the 17 eruptions of the 2005-2010 period have shown that the summit eruptions were relatively well predicted

  8. Could the IMS Infrasound Stations Support a Global Network of Small Aperture Seismic Arrays?

    NASA Astrophysics Data System (ADS)

    J, Gibbons, Steven; Kværna, Tormod; Mykkeltveit, Svein

    2015-04-01

    The infrasound stations of the International Monitoring System are arrays consisting of up to 15 sites and with apertures of up to 3 km. The arrays are distributed remarkably uniformly over the globe and provide excellent coverage of South America, Africa, and Antarctica. This is to say that there are many infrasound arrays in regions many thousands of kilometers from the closest seismic array. Several infrasound arrays are in the immediate vicinity of existing 3-component seismic stations and these provide us with examples of how typical seismic signals look at these locations. We can make idealized estimates of the predicted performance of seismic arrays, consisting of seismometers at each site of the infrasound arrays, by duplicating the signals from the 3-C stations at all sites of the array. However, the true performance of seismic arrays at these sites will depend both upon Signal-to-Noise Ratios of seismic signals and the coherence of both signal and noise between sensors. These properties can only be determined experimentally. Recording seismic data of sufficient quality at many of these arrays may require borehole deployments since the microbarometers in the infrasound arrays are often situated in vaults placed in soft sediments. The geometries of all the current IMS infrasound arrays are examined and compared and we demonstrate that, from a purely geometrical perspective, essentially all the array configurations would provide seismic arrays with acceptable slowness resolution for both regional and teleseismic phase arrivals. Seismic arrays co-located with the infrasound arrays in many regions would likely enhance significantly the seismic monitoring capability in parts of the world where only 3-component stations are currently available. Co-locating seismic and infrasound sensors would facilitate the development of seismic arrays that share the infrastructure of the infrasound arrays, reducing the development and operational costs. Hosting countries might

  9. Teleseismic SKS splitting beneath East Antarctica using broad-band stations around Soya Coast

    NASA Astrophysics Data System (ADS)

    Usui, Y.; Kanao, M.

    2006-12-01

    We observed shear wave splitting of SKS waves from digital seismographs that are recorded at 5 stations around Soya Coast in the Lutzow-Holm Bay, East Antarctica. Their recording systems are composed of a three-component broadband seismometer (CMG-40T), a digital recording unit and a solar power battery supply. The events used were selected from 1999 to 2004 and phase arrival times were calculated using the IASPEI91 earth model (Kennet, 1995). In general, we chose the data from earthquakes with m>6.0 and a distance range 85° < Δ < 130° for the most prominent SKS waves We used the methods of Silver and Chan (1991) for the inversion of anisotropy parameters and estimated the splitting parameters φ (fast polarization direction) and δt (delay time between split waves) assuming a single layer of hexagonal symmetry with a horizontal symmetry axis. The weighted averages of all splitting parameters (φ, δt) for each station are AKR (30±4, 1.30±0.2), LNG (58±6, 1.27±0.2), SKL (67±10, 0.94±0.2), SKV (40±6, 1.28±0.3) and TOT (52±8, 1.26±0.3), where the weights are inversely proportional to the standard deviations for each solution. As compared to typical delay times of SKS waves which show 1.2s (Silver and Chan 1991; Vinnik et al., 1992), the result shows generally the same value. In previous study, Kubo and Hiramatsu (1998) estimate the splitting parameter for Syowa station (SYO), where is located near our using stations in East Antarctica, and the results are (49±3, 0.70±0.1). Although it is consistent with our results for fast polarization direction, δt for our results are large relatively to those of SYO. The difference may be due to either different incident angle or more complex anisotropic structure. We found that fast polarization direction is systematically parallel to coast line in the Lutzow-Holm Bay, East Antarctica, which is consistent with NE-SW paleo compressional stress. The absolute plate motion based on the HS2-NUVEL1 (Gripp and Gordon

  10. A very low-cost and adaptable DIY seismic station

    NASA Astrophysics Data System (ADS)

    Mendez Chazara, Nahum; Castiñeiras, Pedro

    2016-04-01

    . Obviously, there can be also different configurations to fit different needs: From horizontal geophones, to the use of accelerometers to substitute the geophone and miniaturize even less the size of the seismic station. Also, the data can be gathered only by an Arduino board, but then it needs a card reader/writer and a real-time clock (RTC) circuit in order to correctly timestamp the data. In the first semester of 2016, we plan to build several units and deploy them in the field over the Bajo Segura Fault (Spain) and test them over different conditions to better assess the quality of the data.

  11. The Piton de la Fournaise activity from 1985 to 2010. Search and analysis of short-term precursors from the broad-band seismological RER station

    NASA Astrophysics Data System (ADS)

    Roult, G. C.; Peltier, A.; Taisne, B.; Staudacher, T.; Ferrazzini, V.; Di Muro, A.

    2012-12-01

    Piton de la Fournaise volcano (La Réunion Island) is one of the most active basaltic volcanoes, with an average of one eruption every 10 months. This study provides the first exhaustive compilation of all volcanic events (intrusions, eruptions, seismic crises) and related parameters at Piton de la Fournaise in the 1985-2010 period. This compilation has been correlated with the analysis of the records from the very broad-band seismological RER station (Geoscope network), located 8.5 km north of the summit. Our approach allowed us to identify short-term long period seismic precursors for most eruptions and intrusions. After a signal filtering process that consists in removing the instrumental response and the theoretical Earth tides effect, these precursors can be distributed into 4 classes that depend on their waveform and are globally considered as tilt related with magma transfer inside the sub-aerial part of the volcano edifice. The shapes and characteristics of these transient phenomena (time delay, duration or class) exhibit particular features that can be partly related to other simple eruption or intrusion parameters (location, altitude, volume). Statistical analyses of all events (intrusions and eruptions) are then derived. Estimates of acceleration rates of tilt signal at the RER station have been retrieved for eruptions and intrusions, with the challenge of providing a way to differentiate one from the other in real-time. Acceleration rates seem to correlate with eruptive lava flow volume and a threshold value can be determined allowing us to discriminate between intrusions and eruptions, illustrating the interest of analyzing them for real time monitoring. Our study highlights the additional role of external factors like loading and unloading related to the rainy season and stress field evolution due to Earth tides in influencing magma propagation and volcanic activity.

  12. Pseudo-reflection imaging of the Lunar Moho beneath the Apollo seismic stations using deep-moonquake seismic interferometry

    NASA Astrophysics Data System (ADS)

    Nishitsuji, Yohei; Rowe, Charlotte; Wapenaar, Kees; Draganov, Deyan

    2016-04-01

    In 30 years following NASA's Apollo missions, numerous geophysical methods have been applied to determine the depth of the Lunar Moho. These methods, such as travel-time analysis and gravity inversion, have yielded inconsistent estimates. Here, we apply a seismic interferometry technique using body waves. We use deep moonquakes recorded by the Apollo stations to retrieve zero-offset reflection responses beneath each seismic station on the Nearside of the Moon. We call this application deep-moonquake seismic interferometry (DMSI). We present here the first pseudo-reflection imaging of the Lunar Moho, which we interpret to reside at around 50 km depth. Our interpretation agrees with JAXA's SELENE result, and with earlier travel-time studies. Our DMSI results also show lateral inhomogeneity beneath the Moho, suggesting strong scattering within a zone characterized by seismic velocity that exhibits little variation at our resolution scale (0.2-2.0 Hz). This zone is where most of the shallow moonquakes are presumed to be occurring.

  13. Seismic Tomography of Siyazan - Shabran Oil and Gas Region Of Azerbaijan by Data of The Seismic Stations

    NASA Astrophysics Data System (ADS)

    Yetirmishli, Gurban; Guliyev, Ibrahim; Mammadov, Nazim; Kazimova, Sabina; Ismailova, Saida

    2016-04-01

    The main purpose of the research was to build a reliable 3D model of the structure of seismic velocities in the earth crust on the territory of Siyazan-Shabran region of Azerbaijan, using the data of seismic telemetry stations spanning Siyazan-Shabran region (Siyazan, Altiagaj, Pirgulu, Guba, Khinalig, Gusar), including 7 mobile telemetry seismic stations. Interest to the problem of research seismic tomography caused by applied environmental objectives, such as the assessment of geological risks, engineering evaluation (stability and safety of wells), the task of exploration and mining operations. In the study region are being actively developed oil fields, and therefore, there is a risk of technogenic earthquakes. It was performed the calculation of first arrival travel times of P and S waves and the corresponding ray paths. Calculate 1D velocity model which is the initial model as a set of horizontal layers (velocity may be constant or changed linearly with depth on each layer, gaps are possible only at the boundaries between the layers). Have been constructed and analyzed the horizontal sections of the three-dimensional velocity model at different depths of the investigated region. By the empirical method was proposed density model of the sedimentary rocks at depths of 0-8 km.

  14. Investigation of the Seismic Nucleation Phase of Large Earthquakes Using Broadband Teleseismic Data

    NASA Astrophysics Data System (ADS)

    Burkhart, Eryn Therese

    The dynamic motion of an earthquake begins abruptly, but is often initiated by a short interval of weak motion called the seismic nucleation phase (SNP). Ellsworth and Beroza [1995, 1996] concluded that the SNP was detectable in near-source records of 48 earthquakes with moment magnitude (Mw), ranging from 1.1 to 8.1. They found that the SNP accounted for approximately 0.5% of the total moment and 1/6 of the duration of the earthquake. Ji et al [2010] investigated the SNP of 19 earthquakes with Mw greater than 8.0 using teleseismic broadband data. This study concluded that roughly half of the earthquakes had detectable SNPs, inconsistent with the findings of Ellsworth and Beroza [1995]. Here 69 earthquakes of Mw 7.5-8.0 from 1994 to 2011 are further examined. The SNP is clearly detectable using teleseismic data in 32 events, with 35 events showing no nucleation phase, and 2 events had insufficient data to perform stacking, consistent with the previous analysis. Our study also reveals that the percentage of the SNP events is correlated with the focal mechanism and hypocenter depths. Strike-slip earthquakes are more likely to exhibit a clear SNP than normal or thrust earthquakes. Eleven of 14 strike-slip earthquakes (78.6%) have detectable NSPs. In contrast, only 16 of 40 (40%) thrust earthquakes have detectable SNPs. This percentage also became smaller for deep events (33% for events with hypocenter depth>250 km). To understand why certain thrust earthquakes have a visible SNP, we examined the sediment thickness, age, and angle of the subducting plate of all thrust earthquakes in the study. We found that thrust events with shallow (600 m) on the subducting plate tend to have clear SNPs. If the SNP can be better understood in the future, it may help seismologists better understand the rupture dynamics of large earthquakes. Potential applications of this work could attempt to predict the magnitude of an earthquake seconds before it begins by measuring the SNP, vastly

  15. Sequential dome-collapse nuées ardentes analyzed from broadband seismic data, Merapi Volcano, Indonesia

    USGS Publications Warehouse

    Brodscholl, A.; Kirbani, S.B.; Voight, B.

    2000-01-01

    The broadband data were evaluated using the assumption that avalanches with the same source areas and descent paths exhibit a linear relation between source volume and recorded seismic-amplitude envelope area. A result of the analysis is the determination of the volume of selected individual events. From the field surveys, the total volume of the collapsed dome lava is 2.6 Mm3. Discounting the volumetric influence of rockfalls, the average size of the 44 nuées ardentes is therefore about 60,000 m3. The largest collapse event at 10:54 is estimated to involve 260,000 m3, based on an analysis of the seismicity. The remaining 23 phase I events averaged 60,000 m3, with the total volume of all phase I events accounting for 63% of the unstable dome. The 20 phase II events comprised 37% of the total volume and averaged 47,000 m3. The methods described here can be put to practical use in real-time monitoring situations. Broadband data were essential in this study primarily because of the wide dynamic range.

  16. Station corrections for the Katmai Region Seismic Network

    USGS Publications Warehouse

    Searcy, Cheryl K.

    2003-01-01

    Most procedures for routinely locating earthquake hypocenters within a local network are constrained to using laterally homogeneous velocity models to represent the Earth's crustal velocity structure. As a result, earthquake location errors may arise due to actual lateral variations in the Earth's velocity structure. Station corrections can be used to compensate for heterogeneous velocity structure near individual stations (Douglas, 1967; Pujol, 1988). The HYPOELLIPSE program (Lahr, 1999) used by the Alaska Volcano Observatory (AVO) to locate earthquakes in Cook Inlet and the Aleutian Islands is a robust and efficient program that uses one-dimensional velocity models to determine hypocenters of local and regional earthquakes. This program does have the capability of utilizing station corrections within it's earthquake location proceedure. The velocity structures of Cook Inlet and Aleutian volcanoes very likely contain laterally varying heterogeneities. For this reason, the accuracy of earthquake locations in these areas will benefit from the determination and addition of station corrections. In this study, I determine corrections for each station in the Katmai region. The Katmai region is defined to lie between latitudes 57.5 degrees North and 59.00 degrees north and longitudes -154.00 and -156.00 (see Figure 1) and includes Mount Katmai, Novarupta, Mount Martin, Mount Mageik, Snowy Mountain, Mount Trident, and Mount Griggs volcanoes. Station corrections were determined using the computer program VELEST (Kissling, 1994). VELEST inverts arrival time data for one-dimensional velocity models and station corrections using a joint hypocenter determination technique. VELEST can also be used to locate single events.

  17. Placement of Base Stations in Broadband Power Line Communications Access Networks by Means of Multi-criteria Optimization

    NASA Astrophysics Data System (ADS)

    Haidine, Abdelfatteh; Lehnert, Ralf

    Broadband Power Line Communications (B-PLC) technology is an alternative for broadband access networks, allowing bit rates up to currently 200Mbps. This technique uses the wiring of the low-voltage grid in order to offer to the users the telecommunications services, such as Internet, VoIP, VoD, etc. The B-PLC design process is sub-divided into two parts: the Generalized Base Station Placement (GBSP) problem and the PLC Channel Allocation Problem (P-CAP). This paper focuses on GBSP that is modeled as multi-criteria combinatorial optimization problem. Based on our published mathematical modeling, this paper supplies more numerical experiments for the evaluation of Multi-Objective Evolutionary Algorithms (MOEAs) in solving GBSP. Their performance is compared with the single-objective optimization.

  18. Discovery of slow earthquakes by dense high-sensitivity broadband borehole seismic observation network in Japan, NIED Hi-net

    NASA Astrophysics Data System (ADS)

    Obara, K.

    2007-12-01

    National Research Institute for Earth Science and Disaster Prevention (NIED) has constructed the nation-wide high-sensitivity seismograph network (Hi-net) with 700 borehole stations, which uniformly covers the Japanese Islands with a spacing of 20-30 km. The borehole sensor is composed of three-component high-sensitivity velocity seismometer, three-component strong motion accelerometer and horizontal component high-sensitivity accelerometer which is available to measure the ground tilt and long-period seismic waves. The sensor vessel is placed at the bottom of the borehole deeper than 100m. There are four advantages of Hi-net; high sensitivity, high signal-to-noise ratio, broadband property of sensors and high density of stations. As a result, detection capability for micro earthquakes has been dramatically improved and some new geophysical phenomena have been discovered. Most remarkable discovery by Hi-net is wide variety of slow earthquakes; non-volcanic deep low- frequency tremors (LFT) [Obara, 2002], short-term slow slip events (SSE) [Obara et al., 2004], and very low- frequency (VLF) earthquakes [Ito et al., 2007]. These slow earthquakes occur simultaneously with a certain recurrence interval at the transition zone on the deeper plate interface along the strike of the subducting Philippine Sea plate, southwest Japan. The tremor is characterized by randomly wave trains lasting for hours to weeks with a predominant frequency of around 2 Hz. The tremor activity is clustered spatially and temporally within the narrow belt-like zone. Peak of tremor activity recurs with a time interval of six months accompanying to the short-term SSE lasting for a several days. VLF earthquake has a predominant period of 20s and occurs coincident with peak of tremors. During the active stage, the source of LFT migrates with a propagation velocity of around 10km/day along the strike of the plate geometry at the downdip side of the locked seismogenic zone. The space-time property of

  19. Seismic response analysis of NAGRA-Net stations using advanced geophysical techniques

    NASA Astrophysics Data System (ADS)

    Poggi, Valerio; Edwards, Benjamin; Dal Moro, Giancarlo; Keller, Lorenz; Fäh, Donat

    2015-04-01

    In cooperation with the National Cooperative for the Disposal of Radioactive Waste (Nagra), the Swiss Seismological Service (SED) has recently completed the installation of ten new seismological observation stations, three of them including a co-located borehole sensor. The ultimate goal of the project is to densify the existing Swiss Digital Seismic Network (SDSNet) in northern Switzerland, in order to improve the detection of very-low magnitude events and to improve the accuracy of future location solutions. This is strategic for unbiased monitoring of micro seismicity at the locations of proposed nuclear waste repositories. To further improve the quality and usability of the recordings, a seismic characterization of the area surrounding the installation area was performed at each site. The investigation consisted of a preliminary geological and geotechnical study, followed by a seismic site response analysis by means of state-of-the-art geophysical techniques. For the borehole stations, in particular, the characterization was performed by combining different types of active seismic methods (P-S refraction tomography, surface wave analysis, Vertical Seismic Profiling - VSP) with ambient vibration based approaches (wavelet decomposition, H/V spectral ratio, polarization analysis, three-component f-k analysis). The results of all analyses converged to the definition of a mean velocity profile for the site, which was later used for the computation of engineering parameters (travel time average velocity and quarter-wavelength parameters) and the analytical SH-wave transfer function. Empirical site-amplification functions are automatically determined for any station connected to the Swiss seismic networks. They are determined based on building statistical models of systematic site-specific effects in recordings of small earthquakes when compared to the Swiss stochastic ground-motion model. Computed site response is validated through comparison with these empirical

  20. Optimizing Multi-Station Template Matching to Identify and Characterize Induced Seismicity in Ohio

    NASA Astrophysics Data System (ADS)

    Brudzinski, M. R.; Skoumal, R.; Currie, B. S.

    2014-12-01

    As oil and gas well completions utilizing multi-stage hydraulic fracturing have become more commonplace, the potential for seismicity induced by the deep disposal of frac-related flowback waters and the hydraulic fracturing process itself has become increasingly important. While it is rare for these processes to induce felt seismicity, the recent increase in the number of deep injection wells and volumes injected have been suspected to have contributed to a substantial increase of events = M 3 in the continental U.S. over the past decade. Earthquake template matching using multi-station waveform cross-correlation is an adept tool for investigating potentially induced sequences due to its proficiency at identifying similar/repeating seismic events. We have sought to refine this approach by investigating a variety of seismic sequences and determining the optimal parameters (station combinations, template lengths and offsets, filter frequencies, data access method, etc.) for identifying induced seismicity. When applied to a sequence near a wastewater injection well in Youngstown, Ohio, our optimized template matching routine yielded 566 events while other template matching studies found ~100-200 events. We also identified 77 events on 4-12 March 2014 that are temporally and spatially correlated with active hydraulic fracturing in Poland Township, Ohio. We find similar improvement in characterizing sequences in Washington and Harrison Counties, which appear to be related to wastewater injection and hydraulic fracturing, respectively. In the Youngstown and Poland Township cases, focal mechanisms and double difference relocation using the cross-correlation matrix finds left-lateral faults striking roughly east-west near the top of the basement. We have also used template matching to determine isolated earthquakes near several other wastewater injection wells are unlikely to be induced based on a lack of similar/repeating sequences. Optimized template matching utilizes

  1. Seismo-acoustic analysis of the ocean swell sources observed with Romanian infrasound array and seismic stations

    NASA Astrophysics Data System (ADS)

    Ghica, Daniela; Grecu, Bogdan; Popa, Mihaela

    2015-04-01

    Romanian Plostina infrasound array (IPLOR) is deployed in the central part of the country, in Vrancea region. Presently, IPLOR array configuration includes 6 elements equipped with Chaparral Physics sensors and with aperture of about 2.5 km. For the purpose of assessing the IPLOR performance in observing various types of infrasound sources, over five years of data (since June 2009 to present) were processed. Signal interactive analysis was performed using WinPMCC software. The detection results show that the station response was gradually improved, as the number of array elements increased from three to six, and wind noise reduction conditions were enhanced. A larger number of detected signals and a better array resolution at lower frequency were noticed as well. Microbaroms - the interaction of ocean swell with the atmosphere - represent a relevant type of infrasonic source present in the IPLOR detection plots, for which the signal characterization has been enhanced with the array upgrading process. IPLOR detection capability related to this energetic long-period infrasound waves, which propagate over large distances, shows an alternating behavior, being strongly influenced by the upper atmospheric winds, i.e. seasonally dependent stratospheric winds. The ocean swell can be considered as a seismo-acoustic source, leaving an imprint on both seismic and infrasonic recordings. The interaction with the atmosphere generates infrasound (microbarom), while the interaction with the sea floor emits seismic signal (microseism). Microbaroms have a sinusoidal wave character with a dominant period of 5 s. Due to low damping at this period in stratospheric wave duct, microbaroms are observed over large distance ranges up to a few thousand kilometres. Microseisms occur as an increasing of seismic background noise between 2 and 20 s; in this range, primary and secondary peaks, at 5 and 14 s, are observed. Common broad-band seismic data, recorded with Romanian dense seismic

  2. Real-time forecast of aftershocks from a single seismic station signal

    NASA Astrophysics Data System (ADS)

    Lippiello, E.; Cirillo, A.; Godano, G.; Papadimitriou, E.; Karakostas, V.

    2016-06-01

    The evaluation of seismic hazard in the hours following large earthquakes is strongly affected by biases due to difficulties in determining earthquake location. This leads to the huge incompleteness of instrumental catalogs. Here we show that if, on the one hand, the overlap of aftershock coda waves hides many small events, on the other hand, it leads to a well-determined empirical law controlling the decay of the amplitude of the seismic signal at a given site. The fitting parameters of this law can be related to those controlling the temporal decay of the aftershock number, and it is then possible to obtain short-term postseismic occurrence probability from a single recorded seismic signal. We therefore present a novel procedure which, without requiring earthquake location, produces more accurate and almost real-time forecast, in a site of interest, directly from the signal of a seismic station installed at that site.

  3. A method to establish seismic noise baselines for automated station assessment

    USGS Publications Warehouse

    McNamara, D.E.; Hutt, C.R.; Gee, L.S.; Benz, H.M.; Buland, R.P.

    2009-01-01

    We present a method for quantifying station noise baselines and characterizing the spectral shape of out-of-nominal noise sources. Our intent is to automate this method in order to ensure that only the highest-quality data are used in rapid earthquake products at NEIC. In addition, the station noise baselines provide a valuable tool to support the quality control of GSN and ANSS backbone data and metadata. The procedures addressed here are currently in development at the NEIC, and work is underway to understand how quickly changes from nominal can be observed and used within the NEIC processing framework. The spectral methods and software used to compute station baselines and described herein (PQLX) can be useful to both permanent and portable seismic stations operators. Applications include: general seismic station and data quality control (QC), evaluation of instrument responses, assessment of near real-time communication system performance, characterization of site cultural noise conditions, and evaluation of sensor vault design, as well as assessment of gross network capabilities (McNamara et al. 2005). Future PQLX development plans include incorporating station baselines for automated QC methods and automating station status report generation and notification based on user-defined QC parameters. The PQLX software is available through the USGS (http://earthquake. usgs.gov/research/software/pqlx.php) and IRIS (http://www.iris.edu/software/ pqlx/).

  4. A multievent study of broadband electrons observed by the DMSP satellites and their relation to red aurora observed at midlatitude stations

    SciTech Connect

    Shiokawa, K.; Meng, C.; Reeves, G.D.; Rich, F.J.; Yumoto, K.

    1997-07-01

    Broadband electrons during magnetic storms are characterized by an unusually intense flux of precipitating electrons in the broadband energy range from 30 eV to 30 keV near the equatorward edge of the auroral oval (47{degree}{endash}66{degree} magnetic latitude). Broadband electrons were first reported by {ital Shiokawa} {ital et al.} [1996]. In this paper, we report a multievent study of broadband electrons, using particle data obtained by the Defense Meteorological Satellite Program (DMSP) satellites during 23 magnetic storms from January 1989 through May 1992. Twelve broadband electron events are identified. Most of them are observed in the night sector, but some are observed in the morning sector. Particle data for successive polar passes of the DMSP multisatellites are used to show that broadband electrons generally last for less than 30 min and that for some events, they precipitate over a wide range of local times simultaneously. On the basis of a quantitative calculation of optical emissions from electrons in the neutral atmosphere, we conclude that broadband electrons are a possible cause of red auroras observed at midlatitude ground stations. We suggest that broadband electrons are associated with certain substorms during the main phase of magnetic storms. This conjecture comes from observations of H component positive bays and Pi 2 pulsations observed at low-latitude magnetic stations and from magnetic field variations observed at geosynchronous satellites. We conclude that the magnetospheric source of broadband electrons lies within the inner part of the plasma sheet. This conclusion is based on the facts that broadband electrons appear in latitudes where plasma sheet particles were observed before the event and that broadband electrons are observed poleward of the subauroral ion drifts, a position that corresponds to the inner edge of the injected particle layer during storms. (Abstract Truncated)

  5. Analysis of Background Seismic Noise Recorded at the Amundsen-Scott South Pole Station, Antarctica

    NASA Astrophysics Data System (ADS)

    Anderson, K. R.; Aster, R.; Beaudoin, B. C.; Butler, R.

    2006-12-01

    A small array of high frequency seismometers was recently placed around the Amundsen-Scott South Pole Station in order to characterize seismic noise generated by the station during operations. This week long experiment, titled, "South Pole Analysis of Machines" or SPAM was conducted in January of 2006 using equipment provided by IRIS PASSCAL to sample the high frequency noise sources generated at the NSF's research base. These data will be correlated to those observed at the ultra quiet GSN seismic station (QSPA) located 5 miles from the base. The purpose of the experiment is to show that although the QSPA sensors are 5 miles away and nearly 1000 feet deep in the ice, there is still a risk of contamination of the signals by cultural noise from the South Pole research base. A Quiet Sector was established around the QSPA station in order to minimize vibrational noise sources, but there is interest in moving some experiments out into the Quiet Sector. Characterizing the noise sources will help us determine the potential reduction in data quality expected at the QSPA station as experiments move closer to the site. Sensors were placed next to the power generators, aircraft taxiway, large antenna towers, as well as at the base of the new station itself. Sensors were also placed between the research base and the QSPA station to get an idea of the propagation of the noise toward the QSPA station. Several high frequency noise sources are clearly seen on all array elements with a number of very clear spectral lines above 1 Hz. These are primarily associated with snow moving tractors and power generators. Smaller signals are seen that may be related to wind loading on the new South Pole elevated station along with harmonics that appear to be correlated with large air handling equipment in the station. Also evident are air operations with landings, takeoffs, taxi and idling C-130's evident. Although greatly attenuated, almost all of these signals are observed at the QSPA

  6. Calibration of Regional Seismic Stations in the Middle East with Shots in Turkey

    SciTech Connect

    Toksoz, M N; Kuleli, S; Gurbuz, C; Kalafat, D; Nekler, T; Zor, K; Yilmazer, M; Ogutcu, Z; Schultz, C A; Harris, D B

    2003-07-21

    The objective of this project is to calibrate regional travel-times and propagation characteristics of seismic waves in Turkey and surrounding areas in the Middle East in order to enhance detection and location capabilities in the region. Important data for the project will be obtained by large calibration shots in central and eastern Turkey. The first, a two-ton shot, was fired in boreholes near Keskin in central Anatolia on 23 November 2002. The explosives were placed in 14 holes, each 80 m deep, arranged in concentric circular arrays. Ninety temporary seismic stations were deployed within a 300 km radius around the shot. The permanent stations of the Turkish National Seismic Network provided a good azimuthal coverage as well as three radial traverses. Most stations within a radius of 200 km recorded the shot. Travel-time data have been analyzed to obtain a detailed crustal model under the shot and along the profiles. The model gives a 35 km thick crust, characterized by two layers with velocities of 5.0 and 6.4 km/s. The P{sub n} velocity was found to be 7.8 km/s. The crustal thickness decreases to the north where the profile crosses the North Anatolian fault. There is a slight increase in crustal velocities, but no change in crustal thickness to the west. Data analysis effort is continuing to refine the regional velocity models and to obtain station corrections.

  7. Data from deployment of temporary seismic stations in northern Norway and Finland

    SciTech Connect

    Maercklin, N; Mykkeltveit, S; Schweitzer, J; Harris, D B; Rock, D W

    2005-02-11

    This short contribution is a description of data now available in NORSAR's data archives from a temporary deployment during 2002-2004 of six seismic stations in northern Norway and Finland. Explosions in underground as well as open-pit mines in the Khibiny massif of the Kola Peninsula of northwestern Russia are conducted on a frequent and relatively regular basis. It was decided to supplement the network of permanent stations in northern Fennoscandia and northwest Russia with temporarily deployed stations, in order to record these explosions, as well as other mining explosions and natural events occurring in this general area. As shown in Fig. 6.4.1, the six temporary stations were deployed along two profile lines, extending westwards from the Khibini massif. The rationale for this deployment was to collect data to examine distance as well as azimuthal dependence of seismic discriminants. As can be seen from Fig. 6.4.1 the southernmost of the two profile lines runs through the permanent seismic array ARCES in northern Norway.

  8. Engineering for Autonomous Seismic Stations at the IRIS PASSCAL Instrument Center

    NASA Astrophysics Data System (ADS)

    Anderson, K. R.; Carpenter, P.; Beaudoin, B. C.; Parker, T.; Hebert, J.; Childs, D.; Chung, P.; Reusch, A. M.

    2015-12-01

    The NSF funded Incorporated Research Institutions for Seismology (IRIS) through New Mexico Tech operates the PASSCAL Instrument Center (PIC) in Socorro New Mexico. The engineering effort at the PIC seeks to optimize seismic station operations for all portable experiments, include those in extremely remote and harsh polar environments. Recent advances have resulted in improved station design, allowing improved operational efficiencies, data quality return and reduction in station logistics associated with installation, maintenance and decommissioning of stations. These include: Battery and power system designs. Incorporating primary Lithium Thionyl Chloride (LTC) technology with rechargeable Lithium Iron Phosphate (LiFePO4) batteries allows systems to operate in areas with long-term solar autonomy (high latitudes). Development includes charge controller systems to switch between primary and secondary technologies efficiently. Enclosures: Engineered solutions to efficiently manage waste heat, maintain operational environment and provide light-weight and durable housing for seismic instrumentation. Communications: In collaboration with Xeos Technologies Inc., we deliver Iridium-based SOH/Command and Control telemetry as well as full bandwidth seismic data communications in high latitude environments at low power requirements. Smaller-lighter-instrumentation: Through the GEOICE MRI, we are working with Nanometrics on next generation "all-in-one" seismic systems that can be deployed in polar environments - easing logistics, minimizing installation time and improving data quality return for these expensive deployments. All autonomous station designs are openly and freely available at the IRIS PASSCAL webpage (www.passcal.nmt.edu/polar/design-drawings). More information on GEOICE and data quality from various seismometer emplacements will be presented in other posters at this AGU meeting.

  9. Simulation Of Broadband Seismic Wave Propagation In A Deep Mine in Sudbury Ontario Canada

    NASA Astrophysics Data System (ADS)

    Saleh, R.; Chen, H.; Milkereit, B.; Liu, Q.

    2014-12-01

    In an active underground mine, amplitudes and travel times of seismic events are critical parameters that have to be determined at various locations. These parameters are useful to better understand the process of spatial and temporal stress distributions in a mine. In this study, variations of travel time and amplitude of seismic waves derived from the conventional constant velocity models are compared to the ones derived from 3D variable velocity model. The results show a significant variation in seismic energy distribution at the mine due to presence of very strong elastic contrast, and the observed complexity of the propagated seismic waves require the use of a variable velocity model. An active deep mine located in Sudbury Ontario Canada hosted this study. Dense 3D arrays of geophones, which are distributed around ore-bodies, have been monitoring controlled production blasts and microseismic events since the mine has started production. It is shown here that the conventional empirical method used to calculate peak particle velocities and accelerations (PPVs/PPAs), tends to underestimate the intensity of seismic waves in stopes or areas close to blast sites. This could be corrected if a more realistic model was implemented. Comparing the travel time information from recorded events in the past few years showed the temporal changes in the mine velocity model as mining progressed, thus updating the velocity model of the mine is needed if better accuracy of event location is required. In this study, a 2D/3D finite difference modeling method is used.

  10. Geologic interpretation of seismic data, relocation of Route 2, Stations 138-155 in Lancaster, Mass.

    USGS Publications Warehouse

    May, James E.; Linehan, Rev. Daniel

    1950-01-01

    The proposed relocation of the Concord-Westminster Highway, Route 2, in Lancaster, Mass., requires a long, deep cut between stations 138 and 155. A preliminary seismic survey was made of the site in October 1949. At that time five transverses were made along the base-line, and three transverse to it. This work showed an anomalous situation in the vicinity of shot point E. In order to obtain the required additional data to resolve these anomalies, four more seismic transverses were made in November 1949. Two of these were run along the base-line between station 138+52 and station 145+12 in such a way as to yield, in conjugation with the preliminary survey, depth data of a 660-foot transverse. One of the primary functions of this long line was to obtain a reliable bedrock velocity. The other two transverses were transverse to the long transverse. This report comprises all of the seismic and geologic work performed at this site. The work was done as a part of a cooperative program of the Massachusetts Department of Public Works and the United States Geological Survey.

  11. Studies of Seismic Sources in Antarctica Using an Extensive Deployment of Broadband Seismographs

    NASA Astrophysics Data System (ADS)

    Lough, Amanda Colleen

    This dissertation is the first comprehensive study reporting the seismicity of Antarctica utilizing year-round recordings from autonomous instruments installed on the continent itself. I first examine the general seismic nature of the continent using locally deployed seismographs in both East Antarctica and West Antarctica. I detect and locate seismic events using the traditional first arriving impulsive P and S waves as well as events classified as 'slow' earthquakes with no impulsive P-waves. I find evidence of tectonic events in East Antarctica (representing intraplate earthquakes within a stable craton), icequake events in the Transantarctic Mountains (associated with active alpine glaciers), and icequake events at calving glaciers along the coastline. In West Antarctica I find tectonic earthquakes, icequakes, and tectonic events related to volcanism. I do not find evidence of tectonic events in West Antarctica that would indicate rifting is currently active. I also find two main sources of 'slow' seismicity: calving along Vanderford glacier and tidally modulated stick-slip motion of the Whillans Ice Stream. I further examine two types of events found through my review of the seismicity of Antarctica. I show that a cluster of events located in West Antarctica near the Marie Byrd Land linear volcanic chain the Executive Committee Range (ECR) are deep long period seismic events associated with the ongoing volcanism of the ECR. I provide several lines of evidence including the age progression of the exposed volcanic line as well as radar images featuring a recent ash layer supporting the continued magmatic activity in the ECR. My final investigation is into a new type of icequake in East Antarctica associated with wind-glazed small-scale crevasse features. The wave trains are dominated by surface wave energy and an apparent lack of body wave energy. I demonstrate that these events are sourced in the upper firn layers and can be used to determine firn thickness in

  12. Acoustic-Seismic Coupling of Broadband Signals - Analysis of Potential Disturbances during CTBT On-Site Inspection Measurements

    NASA Astrophysics Data System (ADS)

    Liebsch, Mattes; Altmann, Jürgen

    2015-04-01

    For the verification of the Comprehensive Nuclear Test Ban Treaty (CTBT) the precise localisation of possible underground nuclear explosion sites is important. During an on-site inspection (OSI) sensitive seismic measurements of aftershocks can be performed, which, however, can be disturbed by other signals. To improve the quality and effectiveness of these measurements it is essential to understand those disturbances so that they can be reduced or prevented. In our work we focus on disturbing signals caused by airborne sources: When the sound of aircraft (as often used by the inspectors themselves) hits the ground, it propagates through pores in the soil. Its energy is transferred to the ground and soil vibrations are created which can mask weak aftershock signals. The understanding of the coupling of acoustic waves to the ground is still incomplete. However, it is necessary to improve the performance of an OSI, e.g. to address potential consequences for the sensor placement, the helicopter trajectories etc. We present our recent advances in this field. We performed several measurements to record sound pressure and soil velocity produced by various sources, e.g. broadband excitation by jet aircraft passing overhead and signals artificially produced by a speaker. For our experimental set-up microphones were placed close to the ground and geophones were buried in different depths in the soil. Several sensors were shielded from the directly incident acoustic signals by a box coated with acoustic damping material. While sound pressure under the box was strongly reduced, the soil velocity measured under the box was just slightly smaller than outside of it. Thus these soil vibrations were mostly created outside the box and travelled through the soil to the sensors. This information is used to estimate characteristic propagation lengths of the acoustically induced signals in the soil. In the seismic data we observed interference patterns which are likely caused by the

  13. Verifying single-station seismic approaches using Earth-based data: Preparation for data return from the InSight mission to Mars

    NASA Astrophysics Data System (ADS)

    Panning, Mark P.; Beucler, Éric; Drilleau, Mélanie; Mocquet, Antoine; Lognonné, Philippe; Banerdt, W. Bruce

    2015-03-01

    The planned InSight mission will deliver a single seismic station containing 3-component broadband and short-period sensors to the surface of Mars in 2016. While much of the progress in understanding the Earth and Moon's interior has relied on the use of seismic networks for accurate location of sources, single station approaches can be applied to data returned from Mars in order to locate events and determine interior structure. In preparation for the data return from InSight, we use a terrestrial dataset recorded at the Global Seismic Network station BFO, located at the Black Forest Observatory in Germany, to verify an approach for event location and structure determination based on recordings of multiple orbit surface waves, which will be more favorable to record on Mars than Earth due to smaller planetary radius and potentially lower background noise. With this approach applied to events near the threshold of observability on Earth, we are able to determine epicentral distance within approximately 1° (corresponding to ∼60 km on Mars), and origin time within ∼30 s. With back azimuth determined from Rayleigh wave polarization, absolute locations are determined generally within an aperture of 10°, allowing for localization within large tectonic regions on Mars. With these locations, we are able to recover Earth mantle structure within ±5% (the InSight mission requirements for martian mantle structure) using 1D travel time inversions of P and S travel times for datasets of only 7 events. The location algorithm also allows for the measurement of great-circle averaged group velocity dispersion, which we measure between 40 and 200 s to scale the expected reliable frequency range of the InSight data from Earth to Mars data. Using the terrestrial data, we are able to resolve structure down to ∼200 km, but synthetic tests demonstrate we should be able to resolve martian structure to ∼400 km with the same frequency content given the smaller planetary size.

  14. A High-Sensitivity Broad-Band Seismic Sensor for Shallow Seismic Sounding of the Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Pike, W. Thomas; Standley, Ian M.; Banerdt, W. Bruce

    2005-01-01

    The recently undertaken Space Exploration Initiative has prompted a renewed interest in techniques for characterizing the surface and shallow subsurface (0-10s of meters depth) of the Moon. There are several reasons for this: First, there is an intrinsic scientific interest in the subsurface structure. For example the stratigraphy, depth to bedrock, density/porosity, and block size distribution all have implications for the formation of, and geological processes affecting the surface, such as sequential crater ejecta deposition, impact gardening, and seismic settling. In some permanently shadowed craters there may be ice deposits just below the surface. Second, the geotechnical properties of the lunar surface layers are of keen interest to future mission planners. Regolith thickness, strength, density, grain size and compaction will affect construction of exploration infrastructure in terms of foundation strength and stability, ease of excavation, radiation shielding effectiveness, as well as raw material handling and processing techniques for resource extraction.

  15. Seismo-volcano source localization with triaxial broad-band seismic array

    NASA Astrophysics Data System (ADS)

    Inza, L. A.; Mars, J. I.; Métaxian, J. P.; O'Brien, G. S.; Macedo, O.

    2011-10-01

    Seismo-volcano source localization is essential to improve our understanding of eruptive dynamics and of magmatic systems. The lack of clear seismic wave phases prohibits the use of classical location methods. Seismic antennas composed of one-component (1C) seismometers provide a good estimate of the backazimuth of the wavefield. The depth estimation, on the other hand, is difficult or impossible to determine. As in classical seismology, the use of three-component (3C) seismometers is now common in volcano studies. To determine the source location parameters (backazimuth and depth), we extend the 1C seismic antenna approach to 3Cs. This paper discusses a high-resolution location method using a 3C array survey (3C-MUSIC algorithm) with data from two seismic antennas installed on an andesitic volcano in Peru (Ubinas volcano). One of the main scientific questions related to the eruptive process of Ubinas volcano is the relationship between the magmatic explosions and long-period (LP) swarms. After introducing the 3C array theory, we evaluate the robustness of the location method on a full wavefield 3-D synthetic data set generated using a digital elevation model of Ubinas volcano and an homogeneous velocity model. Results show that the backazimuth determined using the 3C array has a smaller error than a 1C array. Only the 3C method allows the recovery of the source depths. Finally, we applied the 3C approach to two seismic events recorded in 2009. Crossing the estimated backazimuth and incidence angles, we find sources located 1000 ± 660 m and 3000 ± 730 m below the bottom of the active crater for the explosion and the LP event, respectively. Therefore, extending 1C arrays to 3C arrays in volcano monitoring allows a more accurate determination of the source epicentre and now an estimate for the depth.

  16. Pattern recognition applied to seismic signals of Llaima volcano (Chile): An evaluation of station-dependent classifiers

    NASA Astrophysics Data System (ADS)

    Curilem, Millaray; Huenupan, Fernando; Beltrán, Daniel; San Martin, Cesar; Fuentealba, Gustavo; Franco, Luis; Cardona, Carlos; Acuña, Gonzalo; Chacón, Max; Khan, M. Salman; Becerra Yoma, Nestor

    2016-04-01

    Automatic pattern recognition applied to seismic signals from volcanoes may assist seismic monitoring by reducing the workload of analysts, allowing them to focus on more challenging activities, such as producing reports, implementing models, and understanding volcanic behaviour. In a previous work, we proposed a structure for automatic classification of seismic events in Llaima volcano, one of the most active volcanoes in the Southern Andes, located in the Araucanía Region of Chile. A database of events taken from three monitoring stations on the volcano was used to create a classification structure, independent of which station provided the signal. The database included three types of volcanic events: tremor, long period, and volcano-tectonic and a contrast group which contains other types of seismic signals. In the present work, we maintain the same classification scheme, but we consider separately the stations information in order to assess whether the complementary information provided by different stations improves the performance of the classifier in recognising seismic patterns. This paper proposes two strategies for combining the information from the stations: i) combining the features extracted from the signals from each station and ii) combining the classifiers of each station. In the first case, the features extracted from the signals from each station are combined forming the input for a single classification structure. In the second, a decision stage combines the results of the classifiers for each station to give a unique output. The results confirm that the station-dependent strategies that combine the features and the classifiers from several stations improves the classification performance, and that the combination of the features provides the best performance. The results show an average improvement of 9% in the classification accuracy when compared with the station-independent method.

  17. Seasonal changes in H/V spectral ratio at high-latitude seismic stations

    NASA Astrophysics Data System (ADS)

    Lee, R. F.; Abbott, R. E.; Knox, H. A.; Pancha, A.

    2014-12-01

    We present results demonstrating seasonal variations in the Horizontal-to-Vertical Spectral Ratio (HVSR) at high-latitude seismic stations. We analyze data from two sites at Poker Flat Research Range, near Fairbanks, Alaska. From the first site, we analyze 3 stations installed by Sandia National Labs (SNL) in a valley with marshy summer conditions. We also analyze the PASSCAL Instrument Center station PIC2, which is installed on rock approximately 3.2 km from the SNL stations. These stations continuously record data at 125 (SNL) and 200 (PIC2) samples per second. Seasonal changes in HVSR at high frequencies (> 20 Hz) appear to be caused by impedance contrasts between frozen and thawed ground. Thawed active layers are known to have slower shear-wave velocities than frozen layers or bedrock. An estimate of active layer thickness at each station is obtained from the quarter-wavelength approximation. We verify the accuracy of this technique by obtaining ground-truth measurements at the sites for both thickness and shear-wave velocity. We use physical probing for the thickness measurements and active-source Refraction-Microtremor (ReMi) surveys for the shear-wave velocities. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

  18. Long range transmission loss of broadband seismic pulses in the Arctic under ice-free conditions.

    PubMed

    Thode, Aaron; Kim, Katherine H; Greene, Charles R; Roth, Ethan

    2010-10-01

    In 2008 the Louis S. St-Laurent (LSSL) surveyed deep Arctic waters using a three-airgun seismic source. Signals from the seismic survey were detected between 400 km and 1300 km range on a directional autonomous acoustic recorder deployed in water 53 m deep off the Alaskan North Slope. Observations of received signal levels between 10-450 Hz versus LSSL range roughly fit a cylindrical transmission loss model plus 0.01 dB/km attenuation in deep ice-free waters, and fit previous empirical models in ice-covered waters. The transition between ice-free and ice-covered propagation conditions shifted 200 km closer to the recorder during the survey. PMID:20968323

  19. Cerreto di Spoleto (Umbria-Italy): Seismic amplification at the ENEA local array stations

    SciTech Connect

    Rinaldis, Dario

    2008-07-08

    The Nerina valley, where Borgo Cerreto is located, is surrounded by the Apennine mount chain at the top of which lies the historical centre of Cerreto di Spoleto. The study is part of a research project aiming at analysing natural disasters and their impact on the Italian cultural heritage. Within the framework of this research project, local seismic records were analysed for both the carbonate ridge and the bordering alluvial valley. The choice of Cerreto di Spoleto as a test site derives from the analysis of Italian seismic hazard maps, obtained in terms of peak ground velocity and taking into account regional geology. The maps highlight the considerable seismic hazard which characterises the Apennine belt and its possible increase due to the effect of alluvial deposits. To this aim, ENEA installed in the 80's an accelerometric array (CODISMA up to 2000 and, in the following years, ETNA; for more detailed description see [1]. The 14 October event, was recorded both at the roof of CSM and at BCT stations. This is important to check the features observed comparing the FAS of acceleration at CSM and BCT during the 26 September events. Unfortunately the station at CSM basement did not record the above mentioned events but several aftershocks were recorded at each array station. Velocimetric records of both ambient noise and small-magnitude earthquakes were analysed in order to identify amplification conditions. The analysis was carried out in the time domain, through directional energy evaluation, and in the frequency domain, through H/V spectral ratios and spectral ratios with respect to a reference station.

  20. Investigating relationships between the seismic "nucleation" phases and breakaway phases of recent Mw 8 earthquakes using global broadband seismic observations

    NASA Astrophysics Data System (ADS)

    Ji, C.

    2012-12-01

    It is known that the far field P wave velocity observations of large earthquakes frequently start with a small interval of weak motion, which was described as "fore-shock", "pre-shock", or seismic nucleation phase (SNP) by various researchers, e.g, Ellsworth and Beroza (1995). The energetic ground motion immediately following this interesting phase was named as "breakaway" phase. Recent global surveys indicate that for about 50% of Mw>7.5 earthquakes their SNP could be observed teleseismically and the distribution of the earthquakes with SNP appears to be correlated with the tectonic environment and focal mechanisms (Ji et al, 2010; Burkhart and Ji, 2011). Here, a multiple double-couple (MDC) algorithm is developed to quantitatively investigate the relationship between the SNPs and "breakaway" phases of 22 Mw>8 earthquakes since 1990. Our preliminary analysis indicates that the average moment acceleration during the first 4 s of the 2011 Mw 9.1 Tohoku earthquake is only about 2% of that associating with subsequent "breakaway" rupture stage. As the rupture of moderate or large earthquakes often initiate at the vicinity of one of their high slip fault patches, i.e., asperities (Mai et al., 2005), this kind of big discrepancies might shed the light on the intrinsic differences between the asperity and the weak zone in its vicinity, as hypothesized by the asperity theory (e.g., Kanamori, 1981).

  1. Broadband calibration of the R/V Marcus G. Langseth four-string seismic sources

    NASA Astrophysics Data System (ADS)

    Tolstoy, M.; Diebold, J.; Doermann, L.; Nooner, S.; Webb, S. C.; Bohnenstiehl, D. R.; Crone, T. J.; Holmes, R. C.

    2009-08-01

    The R/V Marcus G. Langseth is the first 3-D seismic vessel operated by the U.S. academic community. With up to a four-string, 36-element source and four 6-km-long solid state hydrophone arrays, this vessel promises significant new insights into Earth science processes. The potential impact of anthropogenic sound sources on marine life is an important topic to the marine seismic community. To ensure that operations fully comply with existing and future marine mammal permitting requirements, a calibration experiment was conducted in the Gulf of Mexico in 2007-2008. Results are presented from deep (˜1.6 km) and shallow (˜50 m) water sites, obtained using the full 36-element (6600 cubic inches) seismic source. This array configuration will require the largest safety radii, and the deep and shallow sites provide two contrasting operational environments. Results show that safety radii and the offset between root-mean-square and sound exposure level measurements were highly dependent on water depth.

  2. Crustal deformation in the south-central Andes backarc terranes as viewed from regional broad-band seismic waveform modelling

    NASA Astrophysics Data System (ADS)

    Alvarado, Patricia; Beck, Susan; Zandt, George; Araujo, Mario; Triep, Enrique

    2005-11-01

    The convergence between the Nazca and South America tectonic plates generates a seismically active backarc region near 31°S. Earthquake locations define the subhorizontal subducted oceanic Nazca plate at depths of 90-120 km. Another seismic region is located within the continental upper plate with events at depths <35 km. This seismicity is related to the Precordillera and Sierras Pampeanas and is responsible for the large earthquakes that have caused major human and economic losses in Argentina. South of 33°S, the intense shallow continental seismicity is more restricted to the main cordillera over a region where the subducted Nazca plate starts to incline more steeply, and there is an active volcanic arc. We operated a portable broad-band seismic network as part of the Chile-Argentina Geophysical Experiment (CHARGE) from 2000 December to 2002 May. We have studied crustal earthquakes that occurred in the back arc and under the main cordillera in the south-central Andes (29°S-36°S) recorded by the CHARGE network. We obtained the focal mechanisms and source depths for 27 (3.5 < Mw < 5.3) crustal earthquakes using a moment tensor inversion method. Our results indicate mainly reverse focal mechanism solutions in the region during the CHARGE recording period. 88 per cent of the earthquakes are located north of 33°S and at middle-to-lower crustal depths. The region around San Juan, located in the western Sierras Pampeanas, over the flat-slab segment is dominated by reverse and thrust fault-plane solutions located at an average source depth of 20 km. One moderate-sized earthquake (event 02-117) is very likely related to the northern part of the Precordillera and the Sierras Pampeanas terrane boundary. Another event located near Mendoza at a greater depth (~26 km) (event 02-005) could also be associated with the same ancient suture. We found strike-slip focal mechanisms in the eastern Sierras Pampeanas and under the main cordillera with shallower focal depths of ~5

  3. Modernization of the Slovenian National Seismic Network

    NASA Astrophysics Data System (ADS)

    Vidrih, R.; Godec, M.; Gosar, A.; Sincic, P.; Tasic, I.; Zivcic, M.

    2003-04-01

    The Environmental Agency of the Republic of Slovenia, the Seismology Office is responsible for the fast and reliable information about earthquakes, originating in the area of Slovenia and nearby. In the year 2000 the project Modernization of the Slovenian National Seismic Network started. The purpose of a modernized seismic network is to enable fast and accurate automatic location of earthquakes, to determine earthquake parameters and to collect data of local, regional and global earthquakes. The modernized network will be finished in the year 2004 and will consist of 25 Q730 remote broadband data loggers based seismic station subsystems transmitting in real-time data to the Data Center in Ljubljana, where the Seismology Office is located. The remote broadband station subsystems include 16 surface broadband seismometers CMG-40T, 5 broadband seismometers CMG-40T with strong motion accelerographs EpiSensor, 4 borehole broadband seismometers CMG-40T, all with accurate timing provided by GPS receivers. The seismic network will cover the entire Slovenian territory, involving an area of 20,256 km2. The network is planned in this way; more seismic stations will be around bigger urban centres and in regions with greater vulnerability (NW Slovenia, Krsko Brezice region). By the end of the year 2002, three old seismic stations were modernized and ten new seismic stations were built. All seismic stations transmit data to UNIX-based computers running Antelope system software. The data is transmitted in real time using TCP/IP protocols over the Goverment Wide Area Network . Real-time data is also exchanged with seismic networks in the neighbouring countries, where the data are collected from the seismic stations, close to the Slovenian border. A typical seismic station consists of the seismic shaft with the sensor and the data acquisition system and, the service shaft with communication equipment (modem, router) and power supply with a battery box. which provides energy in case

  4. Seismic risk assessment as applied to the Zion Nuclear Generating Station

    SciTech Connect

    Wells, J.

    1984-08-01

    To assist the US Nuclear Regulatory Commission (NRC) in its licensing and evaluation role, the NRC funded the Seismic Safety Margins Research Program (SSMRP) at Lawrence Livermore National Laboratory (LLNL) with the goal of developing tools and data bases to evaluate the risk of earthquake caused radioactive release from a commercial nuclear power plant. This paper describes the SSMRP risk assessment methodology and the results generated by applying this methodology to the Zion Nuclear Generating Station. In addition to describing the failure probabilities and risk values, the effects of assumptions about plant configuration, plant operation, and dependence will be given.

  5. Broad-band calibration of marine seismic sources used by R/V Polarstern for academic research in polar regions

    NASA Astrophysics Data System (ADS)

    Breitzke, Monika; Boebel, Olaf; El Naggar, Saad; Jokat, Wilfried; Werner, Berthold

    2008-08-01

    Air guns and air-gun arrays of different volumes are used for scientific seismic surveys with R/V Polarstern in polar regions. To assess the potential risk of these research activities on marine mammal populations, knowledge of the sound pressure field of the seismic sources is essential. Therefore, a broad-band (0-80 kHz) calibration study was conducted at the Heggernes Acoustic Range, Norway. A GI (2.4 l), a G (8.5 l) and a Bolt gun (32.8 l) were deployed as single sources, 3 GI (7.4 l), 3 G (25.6 l) and 8 VLF™ Prakla-Seismos air guns (24.0 l) as arrays. Each configuration was fired along a line of 3-4 km length running between two hydrophone chains with receivers in 35, 100, 198 and 263 m depth. Peak-to-peak, zero-to-peak, rms and sound exposure levels (SEL) were analysed as functions of range. They show the typical dipole-like directivity of marine seismic sources with amplitude cancellation close to the sea surface, higher amplitudes in greater depths, and sound pressure levels which continuously decrease with range. Levels recorded during the approach are lower than during the departure indicating a shadowing effect of Polarsterns's hull. Backcalculated zero-to-peak source levels range from 224-240 dB re 1 μPa @ 1 m. Spectral source levels are highest below 100 Hz and amount to 182-194 dB re 1 μPa Hz-1. They drop off continuously with range and frequency. At 1 kHz they are ~30 dB, at 80 kHz ~60 dB lower than the peak level. Above 1 kHz amplitude spectra are dominated by Polarstern's self-noise. From the rms and sound exposure levels of the deepest hydrophone radii for different thresholds are derived. For a 180 dB rms-level threshold radii maximally vary between 200 and 600 m, for a 186 dB SEL threshold between 50 and 300 m.

  6. Extracting seismic attenuation coefficients from cross-correlations of ambient noise at linear triplets of stations

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri

    2015-11-01

    We develop and apply an algorithm for deriving interstation seismic attenuation from cross-correlations of ambient noise recorded by linear arrays. Theoretical results on amplitude decay due to attenuation are used to form a linear least-square inversion for interstation QR values of Rayleigh surface waves propagating along linear arrays having three or more stations. The noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength. The inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross-correlation functions within a given frequency band. The background attenuation between noise sources and receivers is effectively cancelled with this method. The site amplification factors are assumed constant (or following similar patterns) in the frequency band of interest. The inversion scheme is validated with synthetic tests using ambient noise generated by ray-theory-based calculations with heterogeneous attenuation and homogenous velocity structure. The interstation attenuation and phase velocity dispersion curves are inverted from cross-correlations of the synthetic data. The method is then applied to triplets of stations from the regional southern California seismic network crossing the Mojave section of the San Andreas fault, and a dense linear array crossing the southern San Jacinto Fault zone. Bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse Q values. The results for the regional stations yield QR values around 25 for a frequency band 0.2-0.36 Hz. The results for the San Jacinto fault zone array give QR values of about 6-30 for frequencies in the range 15-25 Hz.

  7. The seismic wave absorption in the crust and upper mantle in the vicinity of the Kislovodsk seismic station

    NASA Astrophysics Data System (ADS)

    Pavlenko, V. A.; Pavlenko, O. V.

    2016-07-01

    The Q-factor estimates of the Earth's crust and upper mantle as the functions of frequency ( Q( f)) are obtained for the seismic S-waves at frequencies up to 35 Hz. The estimates are based on the data for 40 earthquakes recorded by the Kislovodsk seismic station since 2000. The magnitudes of these events are M W > 3.8, the sources are located in the depth interval from 1 to 165 km, and the epicentral distances range from 100 to 300 km. The Q-factor estimates are obtained by the methods developed by Aki and Rautian et al., which employ the suppression of the effects of the source radiation spectrum and local site responses in the S-wave spectra by the coda waves measured at a fixed lapse time (time from the first arrival). The radiation pattern effects are cancelled by averaging over many events whose sources are distributed in a wide azimuthal sector centered at the receiving site. The geometrical spreading was specified in the form of a piecewise-continuous function of distance which behaves as 1/ R at the distances from 1 to 50 km from the source, has a plateau at 1/50 in the interval from 50-70 km to 130-150 km, and decays as 1 {√ R } beyond 130-150 km. For this geometrical spreading model and some of its modifications, the following Q-factor estimates are obtained: Q( f) 85 f 0.9 at the frequencies ranging from 1 to 20 Hz and Q( f) 75 f 1.0 at the frequencies ranging from 1 to 35 Hz.

  8. Streaky noise in seismic normal mode band observed at Syowa Station, Antarctica

    NASA Astrophysics Data System (ADS)

    Hayakawa, H.; Shibuya, K.; Doi, K.; Aoyama, Y.

    2010-12-01

    Background free oscillations are known as continuous and global signals on noise level in seismic normal mode band. These were found from record of superconducting gravimeter (SG) at Syowa Station, Antarctica in 1998 [Nawa et al. 1998], and then were confirmed at various sites. Other unknown slightly broad spectrum peaks were also found as streak on spectrogram of Syowa SG data in seismic normal mode band. But the feature is not found in gravimeter and seismometer records from any other sites, including IDA gravimeter record at SPA station, Antarctica. New SG (SG058), that is the third generation at Syowa Station, has started to observe since January 2010. The second generation SG (CT43, 2004-2009) had strong drift. The auxiliary barometer was less resolution (0.1 hPa) and its pressure record had a lot of steps and spikes occurring frequently by housing problem. To study in seismic normal mode band, high quality pressure data is needed to remove atmospheric pressure effect to gravity from SG data because a nominal admittance factor for its effect is -3 nm/s^2/hPa. The new barometer of SG058 system has a resolution of 0.001 hPa, and the housing problem has been fixed. In this study, we investigated the unknown streaky noise in seismic normal mode band using spectrograms of the new SG and other data observed at Syowa Station. The slightly broad spectrum peaks are clearly found at 2.5, 3.5, 7.6, 8.2 13.2, 16.7 mHz from the SG data during January - May 2010. Strength of these peaks shows time variation and it is not necessarily for phase to agree with each others. These unknown peaks are not intrinsic noise of the first generation SG (TT70, 1993 - 2003) but are local or regional signal (noise) around Syowa Station. The atmospheric pressure doesn’t have this steaky feature. The sea level variation causes noise level of Syowa SG data to be high by the effect of attraction and loading [Nawa et al. 2003]. Because the noise spectral peaks less than 3 mHz are removed by

  9. Passive seismic experiment - A summary of current status. [Apollo-initiated lunar surface station data

    NASA Technical Reports Server (NTRS)

    Latham, G. V.; Dorman, H. J.; Horvath, P.; Ibrahim, A. K.; Koyama, J.; Nakamura, Y.

    1978-01-01

    The data set obtained from the four-station Apollo seismic network including signals from approximately 11,800 events, is surveyed. Some refinement of the lunar model will result, but its gross features remain the same. Attention is given to the question of a small, molten lunar core, the answer to which remains dependent on analysis of signals from a far side impact. Seventy three sources of repeating, deep moonquakes have been identified, thirty nine of which have been accurately located. Concentrated at depths from 800 to 1000 km, the periodicities of these events have led to the hypothesis that they are generated by tidal stresses. Lunar seismic data has also indicated that the meteoroid population is ten times lower than originally determined from earth based observations. Lunar seismic activity is much lower and mountainous masses show no sign of sinking, in contrast to earth, as a result of the lunar crust being four times thicker. While much work remains to be done, significant correlation between terrestrial and lunar observations can be seen.

  10. The 16 August 1997 Novaya Zemlya seismic event as viewed from GSN stations KEV and KBS

    SciTech Connect

    Hartse, H.E.

    1997-11-01

    Using current and historic seismic records from Global Seismic Network stations KEV and KBS, the authors find that S minus P arrival time comparisons between nuclear explosions and the 16 August 1997 seismic event (m{sub b} {approx} 3.6) from near Novaya Zemlya clearly indicate that (relative to KEV) the 16 August event occurred at least 80 km east of the Russian test site. Including S minus P arrival times from KBS constrains the location to beneath the Kara Sea and in good agreement with previously reported locations, over 100 km southeast of the test site. From an analysis of P{sub n}/S{sub n} waveform ratios at frequencies above 4 Hz, they find that the 16 August event falls within the population of regional earthquakes and is distinctly separated from Novaya Zemlya and other northern Eurasian nuclear explosion populations. Thus, given its location and waveform characteristics, they conclude the 16 August event was an earthquake. The 16 August event was not detected at teleseismic distances, and thus, this event provides a good example of the regional detection, location, and identification efforts that will be required to monitor the Comprehensive Test Ban Treaty below m{sub b} {approx} 4.

  11. Fault Characterization in the Sea of Marmara (Turkey) Using OBS and Land Seismic Stations

    NASA Astrophysics Data System (ADS)

    Pinar, Ali; Yamamoto, Yojiro; Comoglu, Mustafa; Polat, Remzi; Turhan, Fatih; Takahashi, Narumi; Kalafat, Dogan; Citak, Seckin

    2016-04-01

    The fault segments of the North Anatolian fault (NAF) occurring between Tekirdag basin and Kumburgaz basin are investigated using 15 Ocean Bottom Seismic (OBS) stations. The OBS stations were deployed closely around the fault trace of NAF. During the observation period from September, 2014 until July, 2015 more than one thousand microearthquakes were determined. No uniform seismicity pattern was observed along strike and along dip of the fault segments in an area spanning 100 km from East to West of Marmara Sea. The western fault segments exhibit relatively higher and deeper seismic activity while the eastern segment show shallower and relatively lower seismic activity. Integrating the first motion polarity data from the land based stations of Kandilli Observatory and Earthquake Research Institute (KOERI) with the polarity data acquired from the OBS stations the focal mechanisms of 173 micro-earthquakes were determined. Most of the fault plane solutions indicate predominantly strike-slip mechanism. Several clusters of events are identified along the E-W extending NAF. We derive a focal mechanism for the individual events whenever the number of the polarities are sufficient. In addition, simultaneous inversion of the polarities in a cluster are done to retrieve a stress tensor along with focal mechanisms of the individual events in a cluster. A unique cluster of focal mechanisms was obtained from the events taking place in Western High (WH) region located between Tekirdag Basin (TB) and Central Basin (CB). Several features of this cluster are noticeable; 1) the site is the most seismically active part in Marmara Sea, 2) the site is the locus of the deepest events in the Sea of Marmara, 3) the shallower part of this segment is seismically less active, 4) two subgroups of P-axes of focal mechanisms exist; one oriented NW-SE and other oriented in N-S direction despite the proximity of the location of the events giving clues on the faulting dynamics. The N-S oriented P

  12. Eruption dynamics at Mount St. Helens imaged from broadband seismic waveforms: Interaction of the shallow magmatic and hydrothermal systems

    USGS Publications Warehouse

    Waite, G.P.; Chouet, B.A.; Dawson, P.B.

    2008-01-01

    The current eruption at Mount St. Helens is characterized by dome building and shallow, repetitive, long-period (LP) earthquakes. Waveform cross-correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks. Stacked spectra of these events display multiple peaks between 0.5 and 2 Hz that are common to most stations. Lower-amplitude very-long-period (VLP) events commonly accompany the LP events. We model the source mechanisms of LP and VLP events in the 0.5-4 s and 8-40 s bands, respectively, using data recorded in July 2005 with a 19-station temporary broadband network. The source mechanism of the LP events includes: 1) a volumetric component modeled as resonance of a gently NNW-dipping, steam-filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2) a vertical single force attributed to movement of the overlying dome. The VLP source, which also includes volumetric and single-force components, is 250 m deeper and NNW of the LP source, at the SW edge of the 1980s lava dome. The volumetric component points to the compression and expansion of a shallow, magma-filled sill, which is subparallel to the hydrothermal crack imaged at the LP source, coupled with a smaller component of expansion and compression of a dike. The single-force components are due to mass advection in the magma conduit. The location, geometry and timing of the sources suggest the VLP and LP events are caused by perturbations of a common crack system.

  13. Estimation of Broadband Ground Motion at Ocean-bottom Strong-motion Stations for the 2003 Tokachi-oki Earthquake

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Takenaka, H.; Hirata, K.; Watanabe, T.

    2004-12-01

    The 2003 Tokachi-oki earthquake (MJMA8.0) occurred on September 25, 2003 (UT). In this study, we reproduce the broadband ground motion from the earthquake using near-field strong-motion records (accelerograms) at three ocean-bottom stations (KOB1, KOB2 and KOB3) on the sea floor off Kushiro, Hokkaido, installed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The distance and direction from the epicenter to KOB1, KOB2 and KOB3 are 28 km, east-southeast and 83 km,east and 80 km, east-northeast, respectively. Three components (x, y, z) strong motion observation system, enclosed within a cylindrical pressure housing, can record ground motion in broadband frequency range up to DC. The x component is parallel to the axis of the cylinder which is almost horizontal. Since it is suspected that the strong-motion observation systems themselves had moved during the main shock, a simple time-integration of the original acceleration results in wrong velocity and displacement ground motion. So we apply the following processing to the data: We assume that the motion of each strong-motion seismometer can be represented by (1) rotation around the cylinder axis (i.e., roll), (2) tilting of the cylinder (i.e., pitch), and (3) parallel motion. To estimate rotation and tilting, we first use a median-filter for the original records. After the compensation of these movements, the rotated records are integrated into velocity ones. Next, we follow the base-line correction method of Boore (2001) and obtain the ground motion using the amount of submarine upheaval estimated from the two seabed tsunami sensors near KOB1 and KOB3 by Hirata and Baba (2004). By this approach we have successfully obtained broadband velocity and displacement ground motion including DC components. The maximum horizontal (vector resultant) and vertical velocities at KOB1 and KOB3 are estimated to be approximately 160 cm/s, 40 cm/s and 130 cm/s, 20 cm/s, while the corresponding maximum

  14. Supershear rupture in the 24 May 2013 Mw 6.7 Okhotsk deep earthquake: Additional evidence from regional seismic stations

    NASA Astrophysics Data System (ADS)

    Zhan, Zhongwen; Shearer, Peter M.; Kanamori, Hiroo

    2015-10-01

    Zhan et al. (2014a) reported supershear rupture during the Mw 6.7 aftershock of the 2013 Mw 8.3 Sea of Okhotsk deep earthquake, relying heavily on the regional station PET, which played a critical role in constraining the vertical rupture dimension and rupture speed. Here we include five more regional stations and find that the durations of the source time functions derived from these stations are consistent with Zhan et al.'s supershear rupture model. Furthermore, to reduce the nonuniqueness of deconvolution and combine the bandwidths of different stations, we conduct a joint inversion of the six regional stations for a single broadband moment-rate function (MRF). The best fitting MRF, which explains all the regional waveforms well, has a smooth shape without any temporal gaps. The Mw 6.7 Okhotsk deep earthquake is more likely a continuous supershear rupture than a dynamically triggered doublet.

  15. Basin-scale Green's functions from the ambient seismic field recorded by MeSO-net stations

    NASA Astrophysics Data System (ADS)

    Viens, Loïc.; Koketsu, Kazuki; Miyake, Hiroe; Sakai, Shin'ichi; Nakagawa, Shigeki

    2016-04-01

    Seismic waves propagating through the Earth can be significantly affected by velocity structures such as sedimentary basins. We investigate the propagation characteristics of seismic waves across the Kanto basin, Japan, using Green's functions extracted from the ambient seismic field. We use two stations situated on the eastern and southern edges of the basin as virtual sources, and approximately 420 stations, which are mainly a part of the Metropolitan Seismic Observation network (MeSO-net), as receivers. Using seismometers aligned along two straight lines with the virtual sources, we find that several types of waves can be recovered, each with different sensitivities to the layers that compose the basin. We also show that after amplitude calibration, the extracted Green's functions can accurately simulate the seismic waves of two moderate Mw 4-5 shallow earthquakes that occurred close to the virtual sources. Furthermore, we find that the distribution of the 5% damped pseudovelocity response at a period of 6 s computed from the records of each event and the Green's function waveforms have similar amplification patterns. This study supports the fact that dense networks recording continuously the ambient seismic field in metropolitan areas can be used to accurately assess seismic hazard at high spatial resolution.

  16. Chances and limits of single-station seismic event clustering by unsupervised pattern recognition

    NASA Astrophysics Data System (ADS)

    Sick, Benjamin; Guggenmos, Matthias; Joswig, Manfred

    2015-06-01

    Automatic classification of local seismic events which are only recorded at single stations poses great challenges because of weak hypocentre constraints. This study investigates how single-station event clusters relate to geographic hypocentre regions and common source processes. Typical applications arise in local seismic networks where reliable ground truth by a dense temporal network precedes or follows a sparse (permanent) installation. The seismic signals for this study comprise a 3-month subset from a field campaign to map subduction below northern Chile (PISCO '94). Due to favourable ground noise conditions in the Atacama desert, the data set contains an abundance of shallow and deeper earthquakes, and many quarry explosions. Often event signatures overlap, posing a challenge to any signal processing scheme. Pattern recognition must work on reduced seismograms to restrict parameter dimensionality. Continuous parameter extraction based on noise-adapted spectrograms was chosen instead of discrete representation by, for example, amplitudes, onset times or spectral ratios to ensure consideration of potentially hidden features. Visualization of the derived feature vectors for human inspection and template matching algorithms was hereby possible. Because event classes shall comprise earthquake regions regardless of magnitude, clustering based on amplitudes is prevented by proper normalization of feature vectors. Principal component analysis is applied to further reduce the number of features used to train a self-organizing map (SOM). The SOM will topologically arrange prototypes of each event class in a 2-D map. Overcoming the restrictions of this black-box approach, the arranged prototypes could be transformed back to spectrograms to allow for visualization and interpretation of event classes. The final step relates prototypes to ground-truth information, confirming the potential of automated, coarse-grain hypocentre clustering based on single-station

  17. Siting of USArray Seismic Stations in North Carolina and southern Virginia: Experience of NC-1 Team

    NASA Astrophysics Data System (ADS)

    Martin, P.; Howard, J.; Horne, T.

    2012-12-01

    The USArray component of the EarthScope, a transportable array of 400 seismometers installed in a grid about 70 km apart, is in the next two years entering its final stage with station deployment along the Atlantic coast of the United States. Here, we present the experience of the student-faculty team from North Carolina Central University (NCCU) in finding and documenting the suitable sites for the twenty five USArray stations in North Carolina and southern Virginia. The ideal sites are easily accessible yet far from traffic and other sources of noise, with good cell phone coverage, sun exposure and out of flood-prone areas. Although the initial selection of potential locations was done using geospatial mapping and analysis software provided by EarthScope, finding and finalizing the sites involved driving more then 1,000 miles each week for over two months inspecting possible site locations. Aside from driving, the majority of time was spent talking about the EarthScope project and hosting of USArray stations to mostly reluctant landowners. In addition to facing various challenges in finding appropriate sites due to land use issues, such as suburban sprawl of central North Carolina, or topography factors, such as low lying flood prone coastal areas, by far the major challenge was finding the landowners willing to host the seismic station for the necessary three years. In addition to involving students from an HBCU in seismology related project and increasing the visibility of NCCU geophysics program in the University and local community through publicity releases in local media and on university web site, the project had an important outreach component. As North Carolina is located along the seismically quiet, passive Atlantic margin, most residents are not familiar with earthquakes and seismology and the siting experience provided students an opportunity to practice explaining the earthquake research to the general public. The dialog also highlighted science

  18. Seismic reflection exploration of geothermal reservoir at Naval Air Station (NAS) Fallon, Nevada

    NASA Astrophysics Data System (ADS)

    Alay G., Gebregiorgis

    The Primary objective of this study is to increase geologic and tectonic understanding of the geothermal resources at the Naval Air Station (NAS) Fallon, Nevada. The seismic reflection method is employed to study faults, fractures and other tectonic structures in the subsurface in order to identify geothermal drill targets. The efficiency of geothermal systems is strongly dependent on water circulation. Discrete faults may be permeable and provide pathways for water flow depending on the fracture density. It is therefore desirable to detect and map faults and fracture zones and characterize their physical properties when evaluating a geothermal prospect. The seismic data for this project were provided by the NAS environmental research program in Ridgecrest, CA. However, the data collection information was not available so the work includes determining the line geometry and mapping shot points to field files in order to process the data. ProMAX 2D(TM) is the software used to determine the geometry and to process the data. Data processing includes eliminating noise, datum and refraction statics, trace muting, bandpass filter, automatic gain control, amplitude recovery, CMP sorting, velocity analysis and NMO correction, stacking and migration. The results of this study indicate the presence of thick basin fill including Tertiary and Quaternary sediments underlain by Tertiary basalts which are interpreted to be capping rocks for the geothermal reservoirs. This seismic reflection study also reveals the presence of strongly fractured pre-Tertiary basement complex with their top at about 1500m on the north and west and about 900 m on the eastern and southern part of the study area.

  19. The effect of the velocity model, stations geometry, seismic phases and environmental noise level on earthquake location quality

    NASA Astrophysics Data System (ADS)

    D'Alessandro, Antonino; D'Anna, Giuseppe

    2016-04-01

    The precision and accuracy in the estimation of focal parameters mainly depend by the seismic network features and by the velocity model used in the localization process. The number and geometry of the stations that detect a seismic event heavily affect the quality of the localization. To well constrain a hypocenter it is essential that a sufficient number of stations, near and around the epicenter, recording with good signal to noise ratio the event. Large azimuthal gap or the lack of stations near the epicenter can lead to a mistaken location. Low signal to noise ratio due to high-level environmental noise, can lead to large errors in the seismic phases picking thus compromising the precision of the hypocentral location. A not optimized velocity model may lead to strongly biased location affected by important systematic errors. In this work, by means of numerical simulation, will be investigated the effects of these parameters on the quality of the hypocenter estimation. With this goal were simulated different stations geometries, characterized also by different levels of environmental noise, and earthquakes location was carry out by introducing random and systematic errors in both velocity model and seismic phases arrival times. The results of simulations were summarized in focal parameters errors maps.

  20. SEISMIC DATA FOR NUCLEAR EXPLOSION MONITORING IN THE ARABIAN PENINSULA

    SciTech Connect

    Rodgers, A; Al-Amri, A

    2004-07-08

    We report results from the third and final year of our project (ROA0101-35) to collect seismic event and waveform data recorded in and around the Arabian Peninsula. This effort involves several elements. We are working with King Abdulaziz City for Science and Technology to collect data from the Saudi National Seismic Network, that consists of 38 digital three-component stations (27 broadband and 11 short-period). We have an ongoing collaboration with the Kuwait Institute for Scientific Research, which runs the eight station Kuwait National Seismic Network. We installed two temporary broadband stations in the United Arab Emirates (funded by NNSA NA-24 Office of Non-Proliferation & International Security). In this paper we present a summary of data collected under these efforts including integration of the raw data into LLNL's Seismic Research Database and preliminary analysis of souce parameters and earth structure.

  1. Seismic-monitoring changes and the remote deployment of seismic stations (seismic spider) at Mount St. Helens, 2004-2005: Chapter 7 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

    USGS Publications Warehouse

    McChesney, Patrick J.; Couchman, Marvin R.; Moran, Seth C.; Lockhart, Andrew B.; Swinford, Kelly J.; LaHusen, Richard G.; Sherrod, David R.; Scott, William E.; Stauffer, Peter H.

    2008-01-01

    The instruments in place at the start of volcanic unrest at Mount St. Helens in 2004 were inadequate to record the large earthquakes and monitor the explosions that occurred as the eruption developed. To remedy this, new instruments were deployed and the short-period seismic network was modified. A new method of establishing near-field seismic monitoring was developed, using remote deployment by helicopter. The remotely deployed seismic sensor was a piezoelectric accelerometer mounted on a surface-coupled platform. Remote deployment enabled placement of stations within 250 m of the active vent.

  2. The installation campaign of 9 seismic stations around the KTB site to test anisotropy detection by the Receiver Function Technique

    NASA Astrophysics Data System (ADS)

    Bianchi, I.; Anselmi, M.; Apoloner, M. T.; Qorbani, E.; Gribovski, K.; Bokelmann, G.

    2015-09-01

    The project at hand is a field test around the KTB (Kontinentale Tiefbohrung) site in the Oberpfalz, Southeastern Germany, at the northwestern edge of the Bohemian Massif. The region has been extensively studied through the analysis of several seismic reflection lines deployed around the drilling site. The deep borehole had been placed into gneiss rocks of the Zone Erbendorf-Vohenstrauss. Drilling activity lasted from 1987 to 1994, and it descended down to a depth of 9101 m. In our experiment, we aim to recover structural information as well as anisotropy of the upper crust using the receiver function technique. This retrieved information is the basis for comparing the out-coming anisotropy amount and orientation with information of rock samples from up to 9 km depth, and with high-frequency seismic experiments around the drill site. For that purpose, we installed 9 seismic stations, and recorded seismicity continuously for two years from June 2012 to July 2014.

  3. A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985-2010 period. Search and analysis of short-term precursors from a broad-band seismological station

    NASA Astrophysics Data System (ADS)

    Roult, Geneviève; Peltier, Aline; Taisne, Benoît; Staudacher, Thomas; Ferrazzini, Valérie; Di Muro, Andrea

    2012-10-01

    Piton de la Fournaise volcano (La Réunion Island) is one of the most active basaltic volcanoes, with an average of one eruption every 10 months. This study provides the first exhaustive compilation of all volcanic events (intrusions, eruptions, seismic crises) and related parameters at Piton de la Fournaise in the 1985-2010 period. This compilation has been correlated with the analysis of the records from the very broad-band seismological RER station (Geoscope network), located 8.5 km north of the summit. Our approach allowed us to identify short-term long period seismic precursors for most eruptions and intrusions. After a signal filtering process that consists in removing the instrumental response and the theoretical Earth tides effect, these precursors can be distributed into 4 classes that depend on their waveform and are globally considered as tilt related with magma transfer inside the sub-aerial part of the volcano edifice. The shapes and characteristics of these transient phenomena (time delay, duration or class) exhibit particular features that can be partly related to other simple eruption or intrusion parameters (location, altitude, volume). Statistical analyses of all events (intrusions and eruptions) are then derived. Estimates of acceleration rates of tilt signal at the RER station have been retrieved for eruptions and intrusions, with the challenge of providing a way to differentiate one from the other in real-time. Acceleration rates seem to correlate with eruptive lava flow volume and a threshold value can be determined allowing us to discriminate between intrusions and eruptions, illustrating the interest of analyzing them for real-time monitoring. The correlation with the initial seismic crisis marking the opening of magma ascent path was investigated, showing that the delay between the RER transient phenomenon and the start of the seismic crisis has been increasing since the major caldera formation event of 2007. This longer delay may be due to

  4. Continuous H/V Spectral Ratio Analysis of Ambient Noise Recorded by Stationary Seismic Stations to Improve Microzonation Results Obtained by Mobile Stations

    NASA Astrophysics Data System (ADS)

    Van Noten, K.; Lecocq, T.; Meyer, L.; Molron, J.; Camelbeeck, T.

    2015-12-01

    Estimating the resonance frequency and amplification factor of unconsolidated sediments by H/V spectral ratio (HVSR) analysis of seismic ambient noise has been widely used since Nakamura's proposal in 1989. The fundamental frequency (f0) usually correlates well with the thickness of unconsolidated sediments above the bedrock. To measure f0 properly, Nakamura suggested to perform microzonation surveys at night when the artificial microtremor is small and does not fully disrupt the ambient seismic noise. As nightly fieldwork is not always a reasonable demand, we propose an alternative workflow of Nakamura's technique to improve the quality of HVSR results obtained by ambient noise measurements of mobile stations during the day. This new workflow includes the automated H/V calculation of one year of continuous seismic data of a stationary/permanent station located nearby the sites selected for microzonation. By means of an automated python script, the daily, weekly, monthly and seasonally variations of the fundamental frequency and the H/V amplitude at the site where the stationary station is installed are evaluated. Continuous HVSR analysis of sites with constant bedrock depth shows that the changes in the determined f0 and H/V amplitude are dominantly caused by the human behaviour which is stored in the ambient seismic noise (e.g. later onset of traffic in a weekend, quiet Sundays, differences between daily/nightly activity,…). This continuous analysis allows the characterisation of the deviation of the measured f0 to the true f0 throughout the whole year! Consequently, as mobile stations are affected by the same variation of the ambient noise, a correction factor can be applied on the calculated f0 of individual measurements during the microzonation survey and a proper Vs can be estimated. In this presentation, we apply this workflow to two different case studies; i.e. a rural site with a shallow bedrock depth of 30 m and an urban site (Brussels, capital of

  5. Seismic noise level variation in South Korea

    NASA Astrophysics Data System (ADS)

    Sheen, D.; Shin, J.

    2008-12-01

    The variations of seismic background noise in South Korea have been investigated by means of power spectral analysis. The Korea Institute of Geoscience and Mineral Resources (KIGAM) and the Korea Meteorological Administation (KMA) have national wide seismic networks in South Korea, and, in the end of 2007, there are 30 broadband stations which have been operating for more than a year. In this study, we have estimated the power spectral density of seismic noise for 30 broadband stations from 2005 to 2007. Since we estimate PSDs from a large dataset of continuous waveform in this study, a robust PSD estimate of McNamara and Buland (2004) is used. In the frequency range 1-5 Hz, the diurnal variations of noise are observed at most of stations, which are especially larger at coastal stations and at insular than at inland. Some stations shows daily difference of diurnal variations, which represents that cultural activities contribute to the noise level of a station. The variation of number of triggered stations, however, shows that cultural noise has little influence on the detection capability of seismic network in South Korea. Seasonal variations are observed well in the range 0.1-0.5 Hz, while much less found in the frequency range 1-5 Hz. We observed that strong peaks in the range 0.1-0.5 Hz occur at the summer when Pacific typhoons are close to the Korean Peninsula.

  6. Sources of high frequency seismic noise: insights from a dense network of ~250 stations in northern Alsace (France)

    NASA Astrophysics Data System (ADS)

    Vergne, Jerome; Blachet, Antoine; Lehujeur, Maximilien

    2015-04-01

    Monitoring local or regional seismic activity requires stations having a low level of background seismic noise at frequencies higher than few tenths of Hertz. Network operators are well aware that the seismic quality of a site depends on several aspects, among them its geological setting and the proximity of roads, railways, industries or trees. Often, the impact of each noise source is only qualitatively known which precludes estimating the quality of potential future sites before they are tested or installed. Here, we want to take advantage of a very dense temporary network deployed in Northern Alsace (France) to assess the effect of various kinds of potential sources on the level of seismic noise observed in the frequency range 0.2-50 Hz. In September 2014, more than 250 seismic stations (FairfieldNodal@ Zland nodes with 10Hz vertical geophone) have been installed every 1.5 km over a ~25km diameter disc centred on the deep geothermal sites of Soultz-sous-Forêts and Rittershoffen. This region exhibits variable degrees of human imprints from quite remote areas to sectors with high traffic roads and big villages. It also encompasses both the deep sedimentary basin of the Rhine graben and the piedmont of the Vosges massif with exposed bedrock. For each site we processed the continuous data to estimate probability density functions of the power spectral densities. At frequencies higher than 1 Hz most sites show a clear temporal modulation of seismic noise related to human activity with the well-known variations between day and night and between weekdays and weekends. Moreover we observe a clear evolution of the spatial distribution of seismic noise levels with frequency. Basically, between 0.5 and 4 Hz the geological setting modulates the level of seismic noise. At higher frequencies, the amplitude of seismic noise appears mostly related to the distance to nearby roads. Based on road maps and traffic estimation, a forward approach is performed to model the induced

  7. Physically based probabilistic seismic hazard analysis using broadband ground motion simulation: a case study for the Prince Islands Fault, Marmara Sea

    NASA Astrophysics Data System (ADS)

    Mert, Aydin; Fahjan, Yasin M.; Hutchings, Lawrence J.; Pınar, Ali

    2016-08-01

    The main motivation for this study was the impending occurrence of a catastrophic earthquake along the Prince Island Fault (PIF) in the Marmara Sea and the disaster risk around the Marmara region, especially in Istanbul. This study provides the results of a physically based probabilistic seismic hazard analysis (PSHA) methodology, using broadband strong ground motion simulations, for sites within the Marmara region, Turkey, that may be vulnerable to possible large earthquakes throughout the PIF segments in the Marmara Sea. The methodology is called physically based because it depends on the physical processes of earthquake rupture and wave propagation to simulate earthquake ground motion time histories. We included the effects of all considerable-magnitude earthquakes. To generate the high-frequency (0.5-20 Hz) part of the broadband earthquake simulation, real, small-magnitude earthquakes recorded by a local seismic array were used as empirical Green's functions. For the frequencies below 0.5 Hz, the simulations were obtained by using synthetic Green's functions, which are synthetic seismograms calculated by an explicit 2D /3D elastic finite difference wave propagation routine. By using a range of rupture scenarios for all considerable-magnitude earthquakes throughout the PIF segments, we produced a hazard calculation for frequencies of 0.1-20 Hz. The physically based PSHA used here followed the same procedure as conventional PSHA, except that conventional PSHA utilizes point sources or a series of point sources to represent earthquakes, and this approach utilizes the full rupture of earthquakes along faults. Furthermore, conventional PSHA predicts ground motion parameters by using empirical attenuation relationships, whereas this approach calculates synthetic seismograms for all magnitudes of earthquakes to obtain ground motion parameters. PSHA results were produced for 2, 10, and 50 % hazards for all sites studied in the Marmara region.

  8. The current state of seismic monitoring in Switzerland

    NASA Astrophysics Data System (ADS)

    Clinton, J. F.; Haslinger, F.; Diehl, T.; Cauzzi, C.; Plenkers, K.; Kästli, P.; Fäh, D.; Wiemer, S.

    2013-12-01

    The Swiss Seismological Service at ETH Zurich (SED) operates both the national strong motion and broadband permanent seismic networks in Switzerland, as well as supporting local real-time densifications related to projects (such as geothermal explorations and major tunneling) and a mobile pool for national and international deployments related to research and aftershock studies. This submission provides an overview of the current status of network monitoring in Switzerland. A digital high gain network has been operating since 1974 and was upgraded to a continuously recording realtime modern 24 bit broadband network comprising 30 stations from 1999-2002, with station spacing averaging ~30km across the nation. Various improvements and densifications since then have raised the number of broadband sensors to 45 and added co-located strong motion sensors at 13 sites. A notable recent densification is in the NE of Switzerland, where the Swiss National Cooperative for the Disposal of Radioactive Waste (Nagra) have funded an additional 10 broadband stations (including 3 100-200m deep borehole short period stations) in order to reduce the earthquake detection threshold and increase location accuracy in regions that are identified as potential deep nuclear waste storage sites. A strong motion network has been maintained since 1990, comprising 70 12-16 bit triggered sensors located predominantly in free-field urban sites but also including arrays on dams. The free-field network is in the midst of an upgrade (2009-2018), with 30 new stations already installed from the eventual 100 new free-field 24-bit real-time continuous stations. A project has just begun to upgrade the Swiss broadband network, which will co-locate strong-motion sensors at existing broadband sites; assess and implement improvements of installation quality, e.g. by shallow post-hole installations rather than surface vaults; and potentially fill remaining gaps in station coverage. The seismic network has

  9. Seismic azimuthal anisotropy in the oceanic lithosphere and asthenosphere from broadband surface wave analysis of OBS array records at 60 Ma seafloor

    NASA Astrophysics Data System (ADS)

    Takeo, A.; Kawakatsu, H.; Isse, T.; Nishida, K.; Sugioka, H.; Ito, A.; Shiobara, H.; Suetsugu, D.

    2016-03-01

    We analyzed seismic ambient noise and teleseismic waveforms of nine broadband ocean bottom seismometers deployed at a 60 Ma seafloor in the southeastward of Tahiti island, the South Pacific, by the Tomographic Investigation by seafloor ARray Experiment for the Society hotspot project. We first obtained one-dimensional shear wave velocity model beneath the array from average phase velocities of Rayleigh waves at a broadband period range of 5-200 s. The obtained model shows a large velocity reduction at depths between 40 and 80 km, where the lithosphere-asthenosphere boundary might exist. We then estimated shear wave azimuthal anisotropy at depths of 20-100 km by measuring azimuthal dependence of phase velocities of Rayleigh waves. The obtained model shows peak-to-peak intensity of the azimuthal anisotropy of 2%-4% with the fastest azimuth of NW-SE direction both in the lithosphere and asthenosphere. This result suggests that the ancient flow frozen in the lithosphere is not perpendicular to the strike of the ancient mid-ocean ridge but is roughly parallel to the ancient plate motion at depths of 20-60 km. The fastest azimuths in the current asthenosphere are subparallel to current plate motion at depths of 60-100 km. Additional shear wave splitting analysis revealed possible perturbations of flow in the mantle by the hot spot activities and implied the presence of azimuthal anisotropy in the asthenosphere down to a depth of 190-210 km.

  10. Seismic Catalogue and Seismic Network in Haiti

    NASA Astrophysics Data System (ADS)

    Belizaire, D.; Benito, B.; Carreño, E.; Meneses, C.; Huerfano, V.; Polanco, E.; McCormack, D.

    2013-05-01

    with ONEV and BME, installed 4 seismic stations with financial support from the Inter-American Development Bank and the Haitian Government. The 4 stations include strong motion and broad-band sensors, complementing the 8 sensors initially installed. The stations communicate via SATMEX5 with the Canadian HUB, which sends the data back to Haiti with minimum delay. In the immediate future, data transfer will be improved with the installation of a main antenna for data reception and the Seismic Warning Center of Port-au-Prince. A bidirectional satellite communication is considered of fundamental importance for robust real-time data transmission that is not affected in the case of a catastrophic event.

  11. Live multi-station teleconferences at the First Biennial Congress of the Asian-Pacific Hepato-Pancreato-Biliary Association via academic broadband Internet.

    PubMed

    Shimizu, Shuji; Han, Ho-Seong; Okamura, Koji; Yamaguchi, Koji; Tanaka, Masao

    2008-01-01

    Telecommunication is useful, but it is not widely accepted in medicine, partly because image quality is often inadequate for medical use and partly because an initial investment in special equipment is necessary. We conducted live multi-station teleconferences at the First Biennial Congress of the Asian-Pacific Hepato-Pancreato-Biliary Association (APHPBA), using a new telemedicine system which transmits original-quality images in a simple and economical manner. The venue in Japan was linked to Hong Kong, Singapore, and Manila for an endoscopic surgery session, and to Seoul, Beijing, and Taipei for a pancreas transplant session. A digital video transport system (DVTS), which transforms digital video signals directly to Internet protocol, was set up at each station. The presentations were smooth and clear, and were followed by interactive discussion between the four stations for each session. Although our system requires a broadband Internet connection of at least 30 Mbps, a high-speed academic network has been established already in many countries in the Asia-Pacific region and is readily used for research and educational purposes. Application of this high-performance but user-friendly system can make teleconferences more useful and exciting. Telecommunication based on DVTS and a high-speed academic network should revolutionize the future of such conferences as the APHPBA, as well as those in other fields and locations.

  12. A New Standard Installation Method of the Offline Seismic Observation Station in Heavy Snowfall Area of Tohoku Region

    NASA Astrophysics Data System (ADS)

    Hirahara, S.; Nakayama, T.; Hori, S.; Sato, T.; Chiba, Y.; Okada, T.; Matsuzawa, T.

    2015-12-01

    Soon after the 2011 Tohoku earthquake, seismic activity of Tohoku region, NE Japan is induced in the inland area of Akita prefecture and the border area between Fukushima and Yamagata prefectures. We plan to install a total of 80 offline seismic observation stations in these areas for studying the effect of megathrust earthquake on the activities of inland earthquakes. In our project, maintenance will be held twice-a-year for 4 years from 2015 by using 2.0Hz short-period 3-component seismometer, KVS-300 and ultra-low-power data logger, EDR-X7000 (DC12V 0.08W power supply). We installed seismometer on the rock surface or the slope of the natural ground at the possible sites confirmed with low noise level to obtain distinct seismic waveform data. We report an improvement in installation method of the offline seismic observation station in the heavy snowfall area of Tohoku region based on the retrieved data. In the conventional method, seismometer was installed in the hand-dug hole of a slope in case it is not waterproof. Data logger and battery were installed in the box container on the ground surface, and then, GPS antenna was installed on the pole fixed by stepladder. There are risks of the inclination of seismometer and the damage of equipment in heavy snowfall area. In the new method, seismometer is installed in the robust concrete box on the buried basement consists of precast concrete mass to keep its horizontality. Data logger, battery, and GPS antenna are installed on a high place by using a single pole with anchor bolt and a pole mount cabinet to enhance their safety. As a result, total costs of installation are kept down because most of the equipment is reusable. Furthermore, an environmental burden of waste products is reduced.

  13. The Applicability of Incoherent Array Processing to IMS Seismic Array Stations

    NASA Astrophysics Data System (ADS)

    Gibbons, S. J.

    2012-04-01

    The seismic arrays of the International Monitoring System for the CTBT differ greatly in size and geometry, with apertures ranging from below 1 km to over 60 km. Large and medium aperture arrays with large inter-site spacings complicate the detection and estimation of high frequency phases since signals are often incoherent between sensors. Many such phases, typically from events at regional distances, remain undetected since pipeline algorithms often consider only frequencies low enough to allow coherent array processing. High frequency phases that are detected are frequently attributed qualitatively incorrect backazimuth and slowness estimates and are consequently not associated with the correct event hypotheses. This can lead to missed events both due to a lack of contributing phase detections and by corruption of event hypotheses by spurious detections. Continuous spectral estimation can be used for phase detection and parameter estimation on the largest aperture arrays, with phase arrivals identified as local maxima on beams of transformed spectrograms. The estimation procedure in effect measures group velocity rather than phase velocity and the ability to estimate backazimuth and slowness requires that the spatial extent of the array is large enough to resolve time-delays between envelopes with a period of approximately 4 or 5 seconds. The NOA, AKASG, YKA, WRA, and KURK arrays have apertures in excess of 20 km and spectrogram beamforming on these stations provides high quality slowness estimates for regional phases without additional post-processing. Seven arrays with aperture between 10 and 20 km (MJAR, ESDC, ILAR, KSRS, CMAR, ASAR, and EKA) can provide robust parameter estimates subject to a smoothing of the resulting slowness grids, most effectively achieved by convolving the measured slowness grids with the array response function for a 4 or 5 second period signal. The MJAR array in Japan recorded high SNR Pn signals for both the 2006 and 2009 North Korea

  14. Performance of the primary seismic array stations of the IMS network for the year 2015 Part II): An Analyst's perspective

    NASA Astrophysics Data System (ADS)

    Jonathan, Ezekiel; Kebede, Fekadu

    2016-04-01

    Verification of the CTBT is partly dependent on the ability of the automatic system to detect and present correct attributes for all phases that are detected at the stations. This helps in building of more accurate automatic event solutions and thus reducing the work load and time for interactive analysis whilst increasing the quality of bulletins issued out to member states so that they can decide if there are any treaty violations. During interactive analysis automatic event solutions are refined and/or re-estimated by checking the correctness of the associated phase identity, phase arrival time, azimuth and slowness using raw waveform data. This refinement procedure leads analysts to rename, associate, disassociate and manually add seismic arrivals. The final event solution is accepted or rejected based on the existing rules, guidelines and procedures. In addition, new event solutions are built using unassociated signal detections and the raw waveform data during scanning. In this study differences between seismic phases associated to automatically produced SEL3 bulletin and the Late Event Bulletin (LEB) obtained through interactive analysis are investigated using data from all primary seismic array stations of the International Monitoring System (IMS) network during the year 2015. The performance of the network is evaluated from an analyst's perspective by looking at the number of phases that are renamed, manually added, associated, and disassociated by analysts during interactive analysis. The observed differences do shed some light on analysts workload as well as the performance of the primary seismic array of the IMS network. For example, the results indicate that for the Waramunga array station in Australia (WRA) out of a total of 41175 detections associated to saved events in 2015, 13305 (32.3%) of them were renamed during interactive analysis and 7667 were automatic detections that were associated to events by analysts. 1174 detections were manually added

  15. How to make robust splitting measurements for single-station analysis and three-dimensional imaging of seismic anisotropy

    NASA Astrophysics Data System (ADS)

    Monteiller, Vadim; Chevrot, Sébastien

    2010-07-01

    We quantify errors on splitting intensity measurements produced by incoherent noise on horizontal components through a detailed analysis of synthetic seismograms and of SKS and SKKS waves recorded by four permanent broad-band stations. We find that these errors are quite significant, even on high-quality records, because the measurement procedure involves the comparison of radial and transverse components, which are both contaminated by noise. To decrease the level of noise in the data, it is thus recommended to average splitting intensities from waves coming from the same backazimuth. Alternatively, one can analyse stacked radial and transverse components after applying a Wiener filter, which standardizes the waveforms. This is found to be equivalent because the measure of splitting intensity is a linear process. The utilization of Wiener filters reduces variations of apparent splitting resulting from differences in frequency content of the waveforms. It is possible to determine splitting parameters (splitting delays and fast directions) from azimuthal variations of splitting intensity at a particular station. Tests on synthetic seismograms demonstrate that this approach gives unbiased and robust estimates of splitting parameters, in contrast to the Silver and Chan method, which only works on the rare records that have very large signals on their transverse components. The Wolfe and Silver method does not suffer from this limitation and gives the same results as the multichannel splitting intensity method. Analysis of splitting intensities at stations BDFB, BGCA, CAN and ERM gives fast directions that are generally in excellent agreement with those determined with the Wolfe and Silver method. However, at some stations, azimuthal variations of splitting intensities reveal features that are not well captured by the sinusoidal variation representing the average anisotropy beneath the station. This suggests that small-scale lateral variations of anisotropy are present

  16. A fast topographic characterization of seismic station locations in Iran through integrated use of digital elevation models and GIS

    NASA Astrophysics Data System (ADS)

    Karimzadeh, Sadra; Miyajima, Masakatsu; Kamel, Batoul; Pessina, Vera

    2015-10-01

    We present topographic slope positions of seismic stations within four independent networks (IGUT, IIEES, GSI, and BHRC) in Iran through integrated use of digital elevation models and GIS. Since topographic amplification factor (TAF) due to ground surface irregularity could be one of the reasons of earthquake wave amplification and unexpected damage of structures located on the top of ridges in many previous studies, the ridge stations in the study area are recognized using topographic position index (TPI) as a spatial-based scale-dependent approach that helps in classification of topographic positions. We also present the correlation between local topographic positions and V {/s 30} along with Voronoi tiles of two networks (IGUT and IIEES). The obtained results can be profitably used in seismology to establish homogeneous subnetworks based on Voronoi tiles with precise feedback and in the formulation of new ground motion prediction equations with respect to topographic position and topographic amplification factor.

  17. On the seismic design of piping for fossil fired power stations

    SciTech Connect

    Lazzeri, L.

    1996-12-01

    The seismic design criteria are briefly reviewed: the importance of the yielding phenomena on the seismic response is presented. The decisive importance of ductility is confirmed by the field observations. The ductility causes reduction in the response with flattening of the peaks. Some analyses are performed on several piping systems in static equivalent conditions with ZPA loading. Such analyses assume some ductility in the system. Problems are found only for very flexible systems.

  18. A single-station method for the detection, classification and location of fin whale calls using ocean-bottom seismic stations.

    PubMed

    Matias, Luis; Harris, Danielle

    2015-07-01

    Passive seismic monitoring in the oceans uses long-term deployments of Ocean Bottom Seismometers (OBSs). An OBS usually records the three components of ground motion and pressure, typically at 100 Hz. This makes the OBS an ideal tool to investigate fin and blue whales that vocalize at frequencies below 45 Hz. Previous applications of OBS data to locate whale calls have relied on single channel analyses that disregard the information that is conveyed by the horizontal seismic channels. Recently, Harris, Matias, Thomas, Harwood, and Geissler [J. Acoust. Soc. Am. 134, 3522-3535 (2013)] presented a method that used all four channels recorded by one OBS to derive the range and azimuth of fin whale calls. In this work, the detection, classification, and ranging of calls using this four-channel method were further investigated, focusing on methods to increase the accuracy of range estimates to direct path arrivals. Corrections to account for the influences of the sound speed in the water layer and the velocity structure in the top strata of the seabed were considered. The single station method discussed here is best implemented when OBSs have been deployed in deep water on top of seabed strata with low P-wave velocity. These conditions maximize the ability to detect and estimate ranges to fin whale calls. PMID:26233048

  19. A single-station method for the detection, classification and location of fin whale calls using ocean-bottom seismic stations.

    PubMed

    Matias, Luis; Harris, Danielle

    2015-07-01

    Passive seismic monitoring in the oceans uses long-term deployments of Ocean Bottom Seismometers (OBSs). An OBS usually records the three components of ground motion and pressure, typically at 100 Hz. This makes the OBS an ideal tool to investigate fin and blue whales that vocalize at frequencies below 45 Hz. Previous applications of OBS data to locate whale calls have relied on single channel analyses that disregard the information that is conveyed by the horizontal seismic channels. Recently, Harris, Matias, Thomas, Harwood, and Geissler [J. Acoust. Soc. Am. 134, 3522-3535 (2013)] presented a method that used all four channels recorded by one OBS to derive the range and azimuth of fin whale calls. In this work, the detection, classification, and ranging of calls using this four-channel method were further investigated, focusing on methods to increase the accuracy of range estimates to direct path arrivals. Corrections to account for the influences of the sound speed in the water layer and the velocity structure in the top strata of the seabed were considered. The single station method discussed here is best implemented when OBSs have been deployed in deep water on top of seabed strata with low P-wave velocity. These conditions maximize the ability to detect and estimate ranges to fin whale calls.

  20. Single-Station Passive Seismic Stratigraphy for the characterization of subsurface structure of the Valtellina valley (central Alps, northern Italy)

    NASA Astrophysics Data System (ADS)

    Mele, M.; Bini, A.; Bassi, S.; Giudici, M.; Monti, M.; Azzola, M.

    2012-04-01

    The reconstruction of the subsurface structure of alpine valleys plays a key-role in the evaluation of their genesis, entrenchment and tectonic evolution. As a matter of fact, their characterization is strictly dependent on borehole data (water wells, shallow geognostic logs) and land based, deep seismic reflection/refraction lines; unfortunately, the availability of these datasets is often limited by economic and logistical limitations. In this work the subsurface structure of the Valtellina buried valley (central Alps, northern Italy) was investigated by the means of Single-Station Passive Seismic Stratigraphy (S-SPSS), which yields the 1D shear velocity (Vs) profiles, based on the Horizontal to Vertical Spectral Ratios (HVSR) of microtremors produced by Raleigh waves trapped in the ground and provided by measurements of the resonance frequencies produced by a layered seismic stratigraphy. The study area is the central part of Valtellina, W-E oriented along the Insubric line and drained by the Adda river. The sedimentary succession is known by shallow (

  1. Seismic excitation by space shuttles

    USGS Publications Warehouse

    Kanamori, H.; Mori, J.; Sturtevant, B.; Anderson, D.L.; Heaton, T.

    1992-01-01

    Shock waves generated by the space shuttles Columbia (August 13, 1989), Atlantis (April 11, 1991) and Discovery (September 18, 1991) on their return to Edwards Air Force Base, California, were recorded by TERRAscope (Caltech's broadband seismic network), the Caltech-U.S.G.S Southern California Seismic Network (SCSN), and the University of Southern California (USC) Los Angeles Basin Seismic Network. The spatial pattern of the arrival times exhibits hyperbolic shock fronts from which the path, velocity and altitude of the space shuttle could be determined. The shock wave was acoustically coupled to the ground, converted to a seismic wave, and recorded clearly at the broadband TERRAscope stations. The acoustic coupling occurred very differently depending on the conditions of the Earth's surface surrounding the station. For a seismic station located on hard bedrock, the shock wave (N wave) was clearly recorded with little distortion. Aside from the N wave, very little acoustic coupling of the shock wave energy to the ground occurred at these sites. The observed N wave record was used to estimate the overpressure of the shock wave accurately; a pressure change of 0.5 to 2.2 mbars was obtained. For a seismic station located close to the ocean or soft sedimentary basins, a significant amount of shock wave energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave. A distinct topography such as a mountain range was found effective to couple the shock wave energy to the ground. Shock wave energy was also coupled to the ground very effectively through large man made structures such as high rise buildings and offshore oil drilling platforms. For the space shuttle Columbia, in particular, a distinct pulse having a period of about 2 to 3 seconds was observed, 12.5 s before the shock wave, with a broadband seismograph in Pasadena. This pulse was probably excited by the high rise buildings in downtown Los Angeles which were

  2. The development of the Moldova digital seismic network

    NASA Astrophysics Data System (ADS)

    Ilies, I.; Ionescu, C.; Grigore, A. G.

    2009-04-01

    The Republic of Moldova is located in the seismically active region, about 70% of its area is predisposed to shaking intensity 7 - 8 points MSK. Focal zones of the primary seismic danger to the territory of the Republic of Moldova are: Vrancea zone - for the whole of its territory and Dobrogea zone - for the southern part. Monitoring of seismic instrumentation in the republic is provided by the Center of Experimental Seismology, Institute of Geology and Seismology, Academy of Sciences of Moldova. According to the seismic zoning map of the Republic of Moldova, seismic stations "Cahul, Leova" and "Giurgiulesti" located in 8 - degree zone, the central regional station "Chisinau" - in 7 - degree, a station "Soroca" - in 6 - degree zone MSK scale. The development of seismic network since 2004, going through a transition to a modern digital recording, improving working conditions for staff and the construction of new buildings for seismic stations, equipping the new network equipment and improve the methods of collecting and processing seismic data. The works to modernize the network of seismic stations in Moldova were initiated in 2003 with the acquisition of the first three axial digital accelerometer. The device was installed initially in Chisinau, and from it we received the first digital recordings of earthquakes from September 27 and October 27, 2004. In joint efforts with National Institute of Research and Development for Earth Physics from Bucharest, Romania, four seismic stations from Republic of Moldavia was upgraded by broadband and strong motion sensors connected at Q 330 digital recorders that issue continuous recording and real time data stream. Starting from spring of 2008, real time seismic data exchange between IGG Republic of Moldavia and NIEP Romania is running using internet connection.

  3. Landslide seismic magnitude

    NASA Astrophysics Data System (ADS)

    Lin, C. H.; Jan, J. C.; Pu, H. C.; Tu, Y.; Chen, C. C.; Wu, Y. M.

    2015-11-01

    Landslides have become one of the most deadly natural disasters on earth, not only due to a significant increase in extreme climate change caused by global warming, but also rapid economic development in topographic relief areas. How to detect landslides using a real-time system has become an important question for reducing possible landslide impacts on human society. However, traditional detection of landslides, either through direct surveys in the field or remote sensing images obtained via aircraft or satellites, is highly time consuming. Here we analyze very long period seismic signals (20-50 s) generated by large landslides such as Typhoon Morakot, which passed though Taiwan in August 2009. In addition to successfully locating 109 large landslides, we define landslide seismic magnitude based on an empirical formula: Lm = log ⁡ (A) + 0.55 log ⁡ (Δ) + 2.44, where A is the maximum displacement (μm) recorded at one seismic station and Δ is its distance (km) from the landslide. We conclude that both the location and seismic magnitude of large landslides can be rapidly estimated from broadband seismic networks for both academic and applied purposes, similar to earthquake monitoring. We suggest a real-time algorithm be set up for routine monitoring of landslides in places where they pose a frequent threat.

  4. ANSS Backbone Station Quality Assessment

    NASA Astrophysics Data System (ADS)

    Leeds, A.; McNamara, D.; Benz, H.; Gee, L.

    2006-12-01

    In this study we assess the ambient noise levels of the broadband seismic stations within the United States Geological Survey's (USGS) Advanced National Seismic System (ANSS) backbone network. The backbone consists of stations operated by the USGS as well as several regional network stations operated by universities. We also assess the improved detection capability of the network due to the installation of 13 additional backbone stations and the upgrade of 26 existing stations funded by the Earthscope initiative. This assessment makes use of probability density functions (PDF) of power spectral densities (PSD) (after McNamara and Buland, 2004) computed by a continuous noise monitoring system developed by the USGS- ANSS and the Incorporated Research Institutions in Seismology (IRIS) Data Management Center (DMC). We compute the median and mode of the PDF distribution and rank the stations relative to the Peterson Low noise model (LNM) (Peterson, 1993) for 11 different period bands. The power of the method lies in the fact that there is no need to screen the data for system transients, earthquakes or general data artifacts since they map into a background probability level. Previous studies have shown that most regional stations, instrumented with short period or extended short period instruments, have a higher noise level in all period bands while stations in the US network have lower noise levels at short periods (0.0625-8.0 seconds), high frequencies (8.0- 0.125Hz). The overall network is evaluated with respect to accomplishing the design goals set for the USArray/ANSS backbone project which were intended to increase broadband performance for the national monitoring network.

  5. Broad Band Data and Noise Observed with Surface Station and Borehole Station

    NASA Astrophysics Data System (ADS)

    Tunc, Suleyman; Ozel, Oguz; Safa Arslan, Mehmet; Behiye Akşahin, Bengi; Hatipoglu, Mustafa; Cagin Yalcintepe, Ragip; Ada, Samim; Meral Ozel, Nurcan

    2016-04-01

    Marmara region tectonically is very active and many destructive earthquakes happened in the past. North Anatolian Fault Zone crosses the Marmara region and it has three branches. The northern branch passes through Marmara Sea and expected future large earthquake will happen along this fault zone. There is a gap in seismic network in the Marmara region at offshore and onshore areas. We have started broadband borehole seismographic observations to obtain the detailed information about fault geometry and its stick-slip behavior beneath the western Marmara Sea, as a part of the MARsite collaborative Project, namely "New Directions in Seismic Hazard Assessment through Focused Earth Observation in the Marmara Supersite-MARsite". The target area western Marmara of Turkey. In the beginning of the project, we installed eight Broadband surface station around Marmara Sea in April 2014. Then, we added broadband sensor and broadband surface sensor at the same location in November 2014. In this study, we developed a Matlab application to calculate Power Spectral Density against the New Low Noise Model (NLNM) and New High Noise Model (NHNM) determined for one-hour segments of the data. Also we compared ambient noise of broadband borehole sensor and surface broadband sensor.

  6. Seismic Noise Levels Across Antarctica

    NASA Astrophysics Data System (ADS)

    Anthony, R. E.; Aster, R. C.; Wiens, D. A.; Nyblade, A.; Rowe, C. A.

    2011-12-01

    We utilize recently collected west (POLENET) and east Antarctic (AGAP) seismic data from temporary seismic networks, along with existing long-term and previous temporary Antarctic deployments of seismographs to characterize seismic noise across Antarctica, including substantial previously unsampled regions of the continental interior. Power spectral density spectra (PSD) at each broadband station are comprehensively calculated over 1.5 hour, continuous, overlapping time windows to assess noise levels across a period band of ~0.05 to 100 seconds period are estimated and compared to the Peterson (1993) global high- and low- noise models and to noise levels detected elsewhere on Earth. Analysis over hourly to decadal time periods using PSD probability density functions (PDFs; e.g., McNamara and Buland, 2004) allows for the statistical assessment of noise as a function of frequency and time. We assess the resulting time-dependent seismic noise spectral map of the continent in the context of optimizing the location and distribution of future long-term seismic stations in Antarctica. We also assess transient and seasonal variation in primary (~16 s) and secondary (~8 s) microseism peaks, which are both sensitive to near-coastal storms and wave state and to the annual formation and breakup of sea ice.

  7. Systematic Site Characterization at Seismic Stations combined with Empirical Spectral Modeling: critical data for local hazard analysis

    NASA Astrophysics Data System (ADS)

    Michel, Clotaire; Hobiger, Manuel; Edwards, Benjamin; Poggi, Valerio; Burjanek, Jan; Cauzzi, Carlo; Kästli, Philipp; Fäh, Donat

    2016-04-01

    The Swiss Seismological Service operates one of the densest national seismic networks in the world, still rapidly expanding (see http://www.seismo.ethz.ch/monitor/index_EN). Since 2009, every newly instrumented site is characterized following an established procedure to derive realistic 1D VS velocity profiles. In addition, empirical Fourier spectral modeling is performed on the whole network for each recorded event with sufficient signal-to-noise ratio. Besides the source characteristics of the earthquakes, statistical real time analyses of the residuals of the spectral modeling provide a seamlessly updated amplification function w.r. to Swiss rock conditions at every station. Our site characterization procedure is mainly based on the analysis of surface waves from passive experiments and includes cross-checks of the derived amplification functions with those obtained through spectral modeling. The systematic use of three component surface-wave analysis, allowing the derivation of both Rayleigh and Love waves dispersion curves, also contributes to the improved quality of the retrieved profiles. The results of site characterisation activities at recently installed strong-motion stations depict the large variety of possible effects of surface geology on ground motion in the Alpine context. Such effects range from de-amplification at hard-rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the Swiss reference rock velocity model. The derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling. Although many sites are found to exhibit 1D behavior, our procedure allows the detection and qualification of 2D and 3D effects. All data collected during the site characterization procedures in the last 20 years are gathered in a database, implementing a data model proposed for community use at the European scale through NERA and EPOS (www.epos-eu.org). A web stationbook derived from it

  8. Low frequency signals analysis from broadband seismometers records

    NASA Astrophysics Data System (ADS)

    Hsu, Po-Chin

    2016-04-01

    Broadband seismometers record signals over a wide frequency band, in which the high-frequency background noise is usually associated with human activities, such as cars, trains and factory-related activities. Meanwhile, the low-frequency signals are generally linked to the microseisms, atmospheric phenomena and oceanic wave movement. In this study, we selected the broadband seismometer data recorded during the pass of the typhoons with different moving paths, such as Doksuri in 2012, Trami and Kong-Rey in 2013, Hagibis and Matmo in 2014. By comparing the broadband seismic data, the meteorological information, and the marine conditions, we attempt to understand the effect of the meteorological conditions on the low-frequency noise. The result shows that the broadband station located along the southwestern coast of Taiwan usually have relatively higher background noise value, while the inland stations were characterized by lower noise energy. This rapid decay of the noise energy with distance from the coastline suggest that the low frequency noise could be correlated with the oceanic waves. In addition, the noise energy level increases when the distance from the typhoon and the station decreases. The enhanced frequency range is between 0.1~0.3 Hz, which is consistent with the effect caused by the interference of oceanic waves as suggested by the previous studies. This observation indicates that when the pass of typhoon may reinforce the interaction of oceanic waves and caused some influence on the seismic records. The positive correlation between the significant wave height and the noise energy could also give evidence to this observation. However, we found that the noise energy is not necessarily the strongest when the distance from typhoon and the station is the shortest. This phenomenon seems to be related to the typhoon path. When the typhoon track is perpendicular to the coastline, the change of noise energy is generally more significantly; whereas less energy

  9. Towards the Establishment of the Hawaii Integrated Seismic Network for Tsunami, Seismic, and Volcanic Hazard Mitigation

    NASA Astrophysics Data System (ADS)

    Shiro, B. R.; Koyanagi, S. K.; Okubo, P. G.; Wolfe, C. J.

    2006-12-01

    The NOAA Pacific Tsunami Warning Center (PTWC) located in `Ewa Beach, Hawai`i, provides warnings to the State of Hawai`i regarding locally generated tsunamis. The USGS Hawaiian Volcano Observatory (HVO) located in Hawai`i National Park monitors earthquakes on the island of Hawai`i in order to characterize volcanic and earthquake activity and hazards. In support of these missions, PTWC and HVO operate seismic networks for rapidly detecting and evaluating earthquakes for their tsunamigenic potential and volcanic risk, respectively. These existing seismic networks are comprised mostly of short-period vertical seismometers with analog data collection and transmission based on decades-old technology. The USGS National Strong Motion Program (NSMP) operates 31 accelerometers throughout the state, but none currently transmit their data in real time. As a result of enhancements to the U.S. Tsunami Program in the wake of the December 2004 Indian Ocean tsunami disaster, PTWC is upgrading and expanding its seismic network using digital real-time telemetry from broadband and strong motion accelerometer stations. Through new cooperative agreements with partners including the USGS (HVO and NSMP), IRIS, University of Hawai`i, and Germany's GEOFON, the enhanced seismic network has been designed to ensure maximum benefit to all stakeholders. The Hawaii Integrated Seismic Network (HISN) will provide a statewide resource for tsunami, earthquake, and volcanic warnings. Furthermore, because all data will be archived by the IRIS Data Management Center (DMC), the HISN will become a research resource to greater scientific community. The performance target for the enhanced HISN is for PTWC to provide initial local tsunami warnings within 90 seconds of the earthquake origin time. This will be accomplished using real-time digital data transmission over redundant paths and by implementing contemporary analysis algorithms in real-time and near-real-time. Earthquake location, depth, and

  10. The Southern Kansas Seismic Network

    NASA Astrophysics Data System (ADS)

    Terra, F. M.

    2015-12-01

    Historically aseismic Harper and Sumner counties in Southern Kansas experienced a dramatic increase in seismicity beginning in early 2014, coincident with the development of new oil production in the Mississippi Lime Play. In order to better understand the potential relationships between seismicity and oil development, the USGS installed a real-time telemetered seismic network in cooperation with the Kansas Geological Survey, the Kansas Corporation Commission, the Kansas Department of Health and Environment, Harper County, and the Oklahoma Geological Survey. The network began operation in March 2014 with an initial deployment of 5 NetQuakes accelerometers and by July 2014 had expanded to include 10 broadband sites. The network currently has 14 stations, all with accelerometers and 12 with broadband seismometers. The network has interstation spacing of 15 - 25 km and typical azimuthal gap of 80 for well-located events. Data are continuously streamed to IRIS at 200 samples per second from most sites. Earthquake locations are augmented with additional stations from the USGS National Network, Oklahoma Geological Survey Seismic Network, Kansas Seismic Monitoring Network and the Enid Oklahoma Network. Since the spring of 2014 over 7500 earthquakes have been identified with data from this network, 1400 of which have been manually timed and cataloged. Focal depths for earthquakes typically range between 2 and 7 km. The catalog is available at earthquake.usgs.gov/earthquakes/search/ under network code 'Ismpkansas'. The network recorded the largest known earthquake in Harper County, Mw 4.3, on October 2, 2014 and in Sumner County, Mw 4.9, on November 12, 2014. Recorded ground motions at the epicenter of the October earthquake were 0.70 g (PGA) and 12 cm/s (PGV). These high ground motion values agree with near-source recordings made by other USGS temporary deployments in the U. S. midcontinent, indicating a significant shaking hazard from such shallow, moderate

  11. Ambient seismic noise levels: A survey of the permanent and temporary seismographic networks in Morocco, North Africa

    NASA Astrophysics Data System (ADS)

    El Fellah, Y.; Khairy Abd Ed-Aal, A.; El Moudnib, L.; Mimoun, H.; Villasenor, A.; Gallart, J.; Thomas, C.; Elouai, D.; Mimoun, C.; Himmi, M.

    2013-12-01

    Abstract The results, of a conducted study carried out to analyze variations in ambient seismic noise levels at sites of the installed broadband stations in Morocco, North Africa, are obtained. The permanent and the temporary seismic stations installed in Morocco of the Scientific Institute ( IS, Rabat, Morocco), institute de Ciencias de la Tierra Jaume almera (ICTJA, Barcelona, Spain) and Institut für Geophysik (Munster, Germany) were used in this study. In this work, we used 23 broadband seismic stations installed in different structural domains covering all Morocco from south to north. The main purposes of the current study are: 1) to present a catalog of seismic background noise spectra for Morocco obtained from recently installed broadband stations, 2) to assess the effects of experimental temporary seismic vault construction, 3) to determine the time needed for noise at sites to stabilize, 4) to establish characteristics and origin of seismic noise at those sites. We calculated power spectral densities of background noise for each component of each broadband seismometer deployed in the different investigated sites and then compared them with the high-noise model and low-noise Model of Peterson (1993). All segments from day and night local time windows were included in the calculation without parsing out earthquakes. The obtained results of the current study could be used forthcoming to evaluate permanent station quality. Moreover, this study could be considered as a first step to develop new seismic noise models in North Africa not included in Peterson (1993). Keywords Background noise; Power spectral density; Model of Peterson; Scientific Institute; Institute de Ciencias de la Tierra Jaume almera; Institut für Geophysik

  12. Improved characterization of local seismicity using the Dubai Seismic Network, United Arab Emirates

    NASA Astrophysics Data System (ADS)

    Al Khatibi, Eman; Abou Elenean, K. M.; Megahed, A. S.; El-Hussain, I.

    2014-08-01

    In April 2006, Dubai Municipality established a broadband seismological network in Dubai Emirate, United Arab Emirates (UAE). This network was the first seismic network in UAE and consists of four remote seismic stations to observe local and regional seismic activity that may have an effect on Dubai Emirate and the surrounding areas. The network exchanges real-time data with the National Center of Meteorology and Seismology in Abu Dhabi, the Earthquake Monitoring Center in Oman and imports in real-time data from few Global Seismic Network stations, which increases the aperture of the network. In April 2012, Dubai Municipality installed an additional five free-field strong motion stations inside the urban area to estimate and publish real-time ShakeMaps for public and decision makers. Although the local seismic activity from April 2006 to June 2013 reflects low seismic activity with the Emirate, it indicates active tectonics in the relatively aseismic northern Oman Mountains region. A few inland clusters of micro-to-small earthquakes have been identified with the new network. A clear cluster of small-to-moderate earthquakes took place in the eastern part of UAE to the east of Masafi, while two clusters of micro-to-small earthquakes took place at Wadi Nazwa and northern Huwaylat. Focal mechanisms of few well recorded earthquakes in this region indicate normal faulting, generally trending NE in parallel to the transition shear zone between the collision at Zagros and the subduction at the Makran zone.

  13. Pre-instrumental seismicity in Central Africa using felt seisms recorded mainly at the meteorological stations of DRC, Rwanda and Burundi during the colonial period

    NASA Astrophysics Data System (ADS)

    Mulumba, J.-L.; Delvaux, D.

    2012-04-01

    Seismic hazard assessment and mitigation of catastrophes are primarily based on the identification and characterization of seismically active zones. These tasks still rely heavily on the existing knowledge of the seismic activity over the longest possible time period. The first seismic network in Equatorial Africa (IRSAC network) was operated from the Lwiro scientific base on the western shores of Lake Kivu between 1953 and 1963. Before this installation, the historical record of seismic activity in Central Africa is sparse. Even for the relatively short period concerned, spanning only 50-60 years, the historical record is far from being complete. A first attempt has been made by Herrinckx (1959) who compiled a list 960 felt seisms recorded at the meteorological stations between 1915 and 1954 in Congo, Rwanda and Burundi. They were used to draw a density map of felt seisms per square degree. We completed this data base by exploiting the meteorological archives and any available historical report to enlarge the database which now reaches 1513 entries between 1900 and 1959. These entries have been exanimate in order to identify possible historical seismic events. Those are defined by 3 or more quasi-simultaneous records observed over a relatively short distance (a few degrees of latitude/longitude) within a short time difference (few hours). A preliminary list of 115 possible historical seisms has been obtained, identified by 3 to 15 different stations. The proposed location is taken as the average latitude and longitude of the stations where the felt seisms were recorded. Some of the most important ones are associated to aftershocks that have been felt at some stations after the main shocks. The most recent felt seisms have been also recorded instrumentally, which helps to validate the procedure followed. The main difficulties are the magnitude estimation and the possible spatial incompleteness of the recording of felt seism evidence at the margin of the observation

  14. Application of continuous seismic-reflection techniques to delineate paleochannels beneath the Neuse River at US Marine Corps Air Station, Cherry Point, North Carolina

    USGS Publications Warehouse

    Cardinell, Alex P.

    1999-01-01

    A continuous seismic-reflection profiling survey was conducted by the U.S. Geological Survey on the Neuse River near the Cherry Point Marine Corps Air Station during July 7-24, 1998. Approximately 52 miles of profiling data were collected during the survey from areas northwest of the Air Station to Flanner Beach and southeast to Cherry Point. Positioning of the seismic lines was done by using an integrated navigational system. Data from the survey were used to define and delineate paleochannel alignments under the Neuse River near the Air Station. These data also were correlated with existing surface and borehole geophysical data, including vertical seismic-profiling velocity data collected in 1995. Sediments believed to be Quaternary in age were identified at varying depths on the seismic sections as undifferentiated reflectors and lack the lateral continuity of underlying reflectors believed to represent older sediments of Tertiary age. The sediments of possible Quaternary age thicken to the southeast. Paleochannels of Quaternary age and varying depths were identified beneath the Neuse River estuary. These paleochannels range in width from 870 feet to about 6,900 feet. Two zones of buried paleochannels were identified in the continuous seismic-reflection profiling data. The eastern paleochannel zone includes two large superimposed channel features identified during this study and in re-interpreted 1995 land seismic-reflection data. The second paleochannel zone, located west of the first paleochannel zone, contains several small paleochannels near the central and south shore of the Neuse River estuary between Slocum Creek and Flanner Beach. This second zone of channel features may be continuous with those mapped by the U.S. Geological Survey in 1995 using land seismic-reflection data on the southern end of the Air Station. Most of the channels were mapped at the Quaternary-Tertiary sediment boundary. These channels appear to have been cut into the older sediments

  15. The Geoscope Seismic Network

    NASA Astrophysics Data System (ADS)

    Leroy, N.; Stutzmann, E.; Maggi, A.; Vallee, M.; Pardo, C.

    2014-12-01

    The GEOSCOPE observatory provides 32 years of continuous broadband data to the scientific community. The 31 GEOSCOPE stations are installed in 19 countries, across all continents and on islands throughout the oceans. They are equipped with three component very broadband seismometers (STS1 or STS2) and 24 or 26 bit digitizers (Q330HR). Seismometers are installed with warpless base plates, which decrease long period noise on horizontal components by up to 15dB. In most stations, a pressure gauge and a thermometer are also installed. In 2014, we upgraded 4 stations: SSB in France, CAN in Australia, ROCAM in Rodrigues and ECH in France. 27 stations send data in real or near real time to the GEOSCOPE Data Center and to tsunami warning centers. Continuous data of all stations are collected in real time or with a delay by the IPGP Data Center in Paris where they are validated, archived and made available to the international scientific community through different interfaces including web services (see details on http://geoscope.ipgp.fr). In 2015, GEOSCOPE data will also be available through the French national data center RESIF. Seismic noise level of the continuous data are computed every 24 hours and accessible via the geoscope web site. GEOSCOPE data are also validated by comparing real and synthetic body wave waveforms using the SCARDEC method (Vallee et al., 2011). The information on earthquake characteristics, on GEOSCOPE data available for each event and on the waveform fit for each channel are available through the geoscope web portal.

  16. Quantifying Similarity in Seismic Polarizations

    NASA Astrophysics Data System (ADS)

    Eaton, D. W. S.; Jones, J. P.; Caffagni, E.

    2015-12-01

    Measuring similarity in seismic attributes can help identify tremor, low S/N signals, and converted or reflected phases, in addition to diagnosing site noise and sensor misalignment in arrays. Polarization analysis is a widely accepted method for studying the orientation and directional characteristics of seismic phases via. computed attributes, but similarity is ordinarily discussed using qualitative comparisons with reference values. Here we introduce a technique for quantitative polarization similarity that uses weighted histograms computed in short, overlapping time windows, drawing on methods adapted from the image processing and computer vision literature. Our method accounts for ambiguity in azimuth and incidence angle and variations in signal-to-noise (S/N) ratio. Using records of the Mw=8.3 Sea of Okhotsk earthquake from CNSN broadband sensors in British Columbia and Yukon Territory, Canada, and vertical borehole array data from a monitoring experiment at Hoadley gas field, central Alberta, Canada, we demonstrate that our method is robust to station spacing. Discrete wavelet analysis extends polarization similarity to the time-frequency domain in a straightforward way. Because histogram distance metrics are bounded by [0 1], clustering allows empirical time-frequency separation of seismic phase arrivals on single-station three-component records. Array processing for automatic seismic phase classification may be possible using subspace clustering of polarization similarity, but efficient algorithms are required to reduce the dimensionality.

  17. EXPLOITING REAL TIME DATA FROM THE MONTEREY OCEAN FLOOR BROADBAND OBSERVATORY (MOBB)

    NASA Astrophysics Data System (ADS)

    Romanowicz, B. A.; Taira, T.; Dolenc, D.; McGill, P. R.; Neuhauser, D. S.

    2009-12-01

    The Monterey Ocean Bottom Broadband (MOBB) observatory has been acquiring broadband seismic data and auxiliary channels (differential pressure and current meter) since its installation on the ocean floor in Monterey Bay, at 1000 m water depth and 40 km off-shore. Operating autonomously for almost 7 years, the system was successfully connected to the MARS cable (www.mbari.org/mars) on February 26th, 2009, via a 3.6 km extension cable from the MARS science node. The system works as designed and is currently streaming data from seismic, pressure, and water-current sensors to the Berkeley Seismological Laboratory, where it joins data from other broadband stations on land and is archived at the Northern California Earthquake Data Center. The availability of real-time MOBB broadband seismic data provides an opportunity for improving earthquake-monitoring capability in central California, particularly near the Santa Cruz Mountains segment of the San Andreas fault, and the San Gregorio fault. While buried in the mud, MOBB is affected by oceanic sources of noise, which are particularly strong in the infragravity wave band, and care must be taken to reduce this background noise in post-processing. We present examples of data analysis and illustrate how MOBB contributes to the determination of source parameters and regional structure.

  18. Geologic interpretation of seismic data relocation Route 1, cut, Stations 34-52, Copper Mine Road area and northern portion of Ballard Estate in Topsfield, Mass.

    USGS Publications Warehouse

    May, James E.; Linehan, Rev. Daniel

    1950-01-01

    Relocation of the Newburyport Turnpike, Route 1, in Topsfield, Mass., will require a long relatively deep cut between stations 34 and 52. In order to obtain preliminary information on the depths to bedrock and on the nature of the subsurface materials at this site, reconnaissance seismic work was performed in October 1949. Because this reconnaissance work indicated that bedrock might be relatively near the surface over an extensive area where cuttings were to be made, a more detailed seismic study of the area was made in November 1949. The results of both the reconnaissance and detailed seismic work are included in this report. The work was done as part of a cooperative program of the Massachusetts Department of Public Works and the U.S. Geological Survey.

  19. Ceboruco Volcano Seismicity Study using a 3D Single Digital Station

    NASA Astrophysics Data System (ADS)

    Rodriguez-Uribe, M. C.; Nunez-Cornu, F. J.; Nava Pichardo, F. A.; Suarez-Plascencia, C.; Escudero Ayala, C. R.

    2011-12-01

    The Ceboruco stratovolcano (2,280 m.a.s.l.) is located in Nayarit, Mexico, at the west of the Mexican volcanic belt and towards the Sierra de San Pedro southeast. It last eruptive activity was in 1875, and during the following five years it presents superficial activity such as vapor emissions, ash falls and riodacític composition lava flows along the southeast side. We use data recorded from March 2003 to July 2008 at the CEBN triaxial short period digital station located at the southwest side of the volcano. Our final data set consist of 139 volcanic earthquakes. We classified them according waveform characteristics of the east-west horizontal component. We obtained four groups: impulsive arrivals, extended coda, bobbin form, and wave package amplitude modulation earthquakes. The extended coda is the group with more earthquakes and present durations of 50 seconds. Using the moving particle technique, we read the P and S wave arrival times and estimate azimuth arrivals. A P-wave velocity of 3.0 km/s was used to locate the earthquakes, the hypocenters are below the volcanic building within a circular perimeter of 5 km of radius and its depths are calculated relative to the CEBN elevation as follows. The impulsive arrivals earthquakes present hypocenters between 0 and 1 km while the other groups between 0 and 4 km. The epicenters show similar directions as the tectonic structures of the area (Tepic-Zacoalco Graben and regional faults). Results suggest fluid activity inside the volcanic building that could be related to fumes on the volcano. We conclude that the Ceboruco volcano is active. Therefore, it should be continuously monitored due to the risk that represent to the surrounding communities and economic activities.

  20. Seismic Noise Analysis and Reduction through Utilization of Collocated Seismic and Atmospheric Sensors at the GRO Chile Seismic Network

    NASA Astrophysics Data System (ADS)

    Farrell, M. E.; Russo, R. M.

    2013-12-01

    gain insight into how local atmospheric conditions couple with the ground to generate seismic noise, and to explore strategies for reducing this noise post data collection. Comparison of spectra of atmospheric data streams to the three broadband seismic channels for continuous signals recorded during May and June of 2013 shows high coherence between infrasound signals and time variation of air pressure (dP/dt) that we calculated from the air pressure data stream. Coherence between these signals is greatest for the east-west component of the seismic data in northern Chile. Although coherence between seismic, infrasound, and dP/dt is lower for all three seismic channels at other GRO Chile stations, for some of the data streams coherence can jump as much as 6 fold for certain frequency bands, with a common 3-fold increase for periods shorter than 10 seconds and the occasional 6-fold increase at long or very long periods.

  1. Seismicity of southern Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Lavayssiere, A.; Gallacher, R. J.; Keir, D.; Ebinger, C. J.; Drooff, C.; Khalfan, M.; Bull, J. M.

    2015-12-01

    Global seismic networks document frequent and unusually deep earthquakes in East African rift sectors lacking central volcanoes. The deep seismicity means that we can use earthquakes to probe the geometry and kinematics of fault systems throughout the crust, and to understand the distribution of strain between large offset border fault systems and intrabasinal faults. The southern Tanganyika rift zone has the highest seismicity rate within East Africa during the period 1973-present, yet earlier temporary seismometer networks have been too sparse in space and time to relocate earthquakes with location and depth errors of < 5-10 km. We address this issue by recording seismicity of southern Lake Tanganyika since June 2014 using a network at 12 broadband seismic stations. The distribution of earthquakes shows that deformation primarily occurs on large offset border faults beneath the lake. Subsidiary earthquake activity occurs along the subparrallel Rukwa graben, and beneath the NE-SW striking Mweru rift. The distribution of earthquakes suggests the southern end of lake Tanganyika is characterized by a network of intersecting NNW and NE striking faults. The depths of earthquakes are distributed throughout the crust, consistent with the relatively strong lithosphere.

  2. A multi-station matched filter and coherent network processing approach to the automatic detection and relative location of seismic events

    NASA Astrophysics Data System (ADS)

    Gibbons, Steven J.; Näsholm, Sven Peter; Kværna, Tormod

    2014-05-01

    Correlation detectors facilitate seismic monitoring in the near vicinity of previously observed events at far lower detection thresholds than are possible using the methods applied in most existing processing pipelines. The use of seismic arrays has been demonstrated to be highly beneficial in pressing down the detection threshold, due to superior noise suppression, and also in eliminating vast numbers of false alarms by performing array processing on the multi-channel output of the correlation detectors. This last property means that it is highly desirable to run continuous detectors for sites of repeating seismic events on a single-array basis for many arrays across a global network. Spurious detections for a given signal template on a single array can however still occur when an unrelated wavefront crosses the array from a very similar direction to that of the master event wavefront. We present an algorithm which scans automatically the output from multiple stations - both array and 3-component - for coherence between the individual station correlator outputs that is consistent with a disturbance in the vicinity of the master event. The procedure results in a categorical rejection of an event hypothesis in the absence of support from stations other than the one generating the trigger and provides a fully automatic relative event location estimate when patterns in the correlation detector outputs are found to be consistent with a common event. This coherence-based approach removes the need to make explicit measurements of the time-differences for single stations and this eliminates a potential source of error. The method is demonstrated for the North Korea nuclear test site and the relative event location estimates obtained for the 2006, 2009, and 2013 events are compared with previous estimates from different station configurations.

  3. Earth Analog Seismic Deployment for InSight's Mars seismic installation

    NASA Astrophysics Data System (ADS)

    Kedar, S.; Bradford, S. C.; Clayton, R. W.; Davis, P. M.; Ervin, J.; Kawamura, T.; Lognonne, P. H.; Lorenz, R. D.; Mimoun, D.; Murdoch, N.; Roberson, T.; Stubailo, I.; Van Buren, D.

    2014-12-01

    InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) is a NASA Discovery Program mission that will place a single geophysical lander on Mars to study its deep interior. InSight's main experiment is the Seismic Experiment for Interior Structure (SEIS), which will robotically place a broadband seismometer provided by the French Space Agency (CNES) on the Martian surface. SEIS will operate on the surface for a full Mars year. Installing and operating a seismometer on Mars imposes constraints rarely considered in terrestrial seismic installations. The InSight project has therefore conducted a terrestrial analog field deployment exercise to better understand and prepare for the distinctive challenges that placing a broadband seismometer in a Mars-like configuration and environment would pose. The exercise was conducted in two phases at NASA's Goldstone facility in the Southern California Mojave desert. In the first phase we have installed a surface geophysical station including a broadband seismometer, a microbarometer, anemometer, and thermal sensors in a configuration resembling the InSight's geophysical station. The site was located in an exposed location with rough surface and subsurface terrain. It was in close proximity to Goldstone permanent seismic station (GSC) that provided a ground-truth measurement. In the second phase, the installation was moved to a dry lakebed where the geophysical conditions mimic the expected geophysical environment of InSight's target landing site on Mars. We will present a summary of lessons learned so far from our analog deployment exercise. The data analysis emphasizes several aspects of key importance to the InSight mission: (1) Exploring strategies to mitigate environmental noise sources; (2) Recognizing noise sources that might be introduced by the InSight lander (solar panel flutter); (3) Identifying weak geophysical signals with low SNR above the environmental noise; (4) Using non tectonic

  4. Geologic interpretations of seismic data Route 128 (Northern Circumferential Highway) cut, and Hopkins Street grade separation stations 1-18 in Wakefield, Mass.

    USGS Publications Warehouse

    May, James E.; Lineham, Rev. Daniel

    1950-01-01

    The completion of a segment of the Northern Circumferential Highway, Route 126, in Wakefield, Mass., requires an underpass bridge at Hopkins Street, Station 5+50. The plan of the project shows approximately 1800 feet if approach cuts between stations 1 and 18. In October 1945 a preliminary seismic study was made of a segment of this cut between stations 6+50 and 13+30. Four profiles were made at this time and a report was submitted by Newton E. Chute and Rev. Daniel Linhan (file report of January 15). This work showed a relatively shallow (in general, 6 to 12 feet in depth) somewhat irregular bedrock surface between stations 6+50 and 13+50. That data indicated that much of this segment of the cut will be in bedrock. In order to obtain more complete data for the preparation of detailed estimates on the amount of bedrock to be excavated for this segment of the cut, and also to obtain sufficient data for the unexplored segment of the cut, 21 additional seismic traverses were made in September 1949. The present report contains only the results obtained from this later work. The work was performed as a part of a cooperative program of the Massachusetts Department of Public Works and the United States Geological Survey.

  5. Monitoring seismic velocity changes caused by the 2014 Northern Aegean earthquake using continuous ambient noise records

    NASA Astrophysics Data System (ADS)

    Evangelidis, Christos; Daskalakis, Emmanouil; Tsogka, Chrysoula

    2016-04-01

    The 24 May 2014 Northern Aegean earthquake (6.9 Mw), an event on the Northern Aegean Trough (NAT), ruptured on two different fault segments with a total ruptured length of ~100 km. For the second delayed segment, rupture propagated eastward from the hypocenter for ˜65 km with a supershear velocity (5.5 km/s). Low-aftershock seismicity on the supershear segment implies a simple and linear fault geometry there. An effort to monitor temporal seismic velocity changes across the ruptured area of the Northern Aegean earthquake is underway. In recent years, neighboring seismic broadband stations near active faults have been successfully used to detect such changes. The crosscorrelation functions (CCF) of ambient noise records between stations yields the corresponding traveltimes for those inter-station paths. Moreover, the auto-correlation functions (ACF) at each station produce the seismic responce for a coincident source and receiver position. Possible temporal changes of the measured traveltimes from CCFs and ACFs correspond to seismic velocity changes. Initially, we investigate the characteristics and sources of the ambient seismic noise as recorded at permanent seismic stations installed around NAT at the surrounding islands and in mainland Greece and Turkey. The microseismic noise levels show a clear seasonal variation at all stations. The noise levels across the double frequency band (DF; period range 4-8 s) reflect the local sea-weather conditions within a range of a few hundred kilometers. Three years of continuous seismic records framing the main shock have been analysed from ~15 stations within a radius of 100 km from the epicentre. We observe a clear decrease of seismic velocities most likely corresponding to the co-seismic shaking. The spatial variation of this velocity drop is imaged from all inter-station paths that correspond to CCF measurements and for station sites that correspond to ACF measurements. Thus, we explore a possible correlation between co-seismic

  6. UNIBRA - the German contribution to the AlpArray Seismic Network

    NASA Astrophysics Data System (ADS)

    Friederich, Wolfgang; Korn, Michael; Meier, Thomas; Plenefisch, Thomas; Ritter, Joachim; Rümpker, Georg; Thomas, Christine; Tilmann, Frederik; Wassermann, Joachim

    2016-04-01

    AlpArray is a European initiative to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system (cited from the AlpArray Science Plan). The core of the AlpArray project is a dense seismic network covering the entire Alpine region including its forelands. The network is composed of about 600 broadband seismic sensors of which 280 are operated permanently by national institutions and the remaining 320 are deployed temporarily by project partners for a time span of at least 2 years. In a joint effort, German universities contribute 71 temporary stations to the AlpArray Seismic Network, of which 55 are located in southern Germany and 16 in Austria. The instrumentation of the stations is heterogeneous and comprises Streckeisen, Nanometrics and Guralp sensors operated with EarthData, Nanometrics and Quanterra data loggers. The instruments are installed in remote areas and rarely used buildings with power supply. Some stations transfer data via mobile internet connection. The data will be collected at national EIDA centers which also serve as nodes for dissemination of data to the members of the AlpArray working group. Here, we describe installation procedures and setting of the German UNIBRA (UNIversity BRoadband Array) stations. In addition, we present noise characteristics and first records of teleseismic earthquakes. The descriptions may serve as a reference for later work with data from the AlpArray Seismic Network.

  7. Regionalization and calibration of seismic discriminants, path effects and signal-to-noise for station ABKT (Alibek, Turkmenistan)

    SciTech Connect

    Rodgers, A.J.; Walter, W.R.

    1997-07-01

    We report measurements and analysis of regional seismic phase amplitude ratios and signal-to-noise for earthquakes observed at the International Monitoring System primary station ABKT (Alibek, Turkmenistan). We measured noise and phase amplitudes of the regional phases Pn, Pg, Sn, and Lg in four frequency bands between 0.75-9.0 Hz. Measurements were made in both the time and frequency domains. The spatial variation of amplitude ratios (e.g., Pn/Lg, Pg/Lg, Pn/Sn, Pg/Sn) and signal-to-noise (phase/noise) reveal significant path effect differences between the Hindu Kush, Kazahk Platform, Iranian Plateau and Caspian Sea. In order to represent this behavior, we have investigated several techniques for characterizing the data. These techniques are: 1) correlation with along-path distance and waveguide properties; 2) sector analysis; and 3) spatial averaging. Along-path waveguide properties, such as mean elevation and rms topographic slope are found to be the strongest factors related to Pg/Lg amplitude ratios at the lowest frequencies (<3.0 Hz). Other path properties such as mean crustal thickness and basement depth are not strongly correlated with Pg/Lg ratios. For sector analysis we divided the data into four (4) azimuthal sectors and characterized the data within each sector by a distance trend. Sectors were chosen based on the behavior of Pn/Lg, Pg/Lg and Pn/Sn amplitude ratios as well as topographic and tectonic character. Results reveal significant reduction (up to a factor of two) in the scatter of the Pn/Lg and Pg/Lg amplitude ratios for the sectorized data compared to the entire data set from all azimuths. Spatial averaging involves smoothing and interpolation for the ratios projected at the event location. Methods such as cap averaging and kriging will be presented at the meeting. 7 refs., 6 figs.

  8. Seismic source study of the Racha-Dzhava (Georgia) earthquake from aftershocks and broad-band teleseismic body-wave records: An example of active nappe tectonics

    USGS Publications Warehouse

    Fuenzalida, H.; Rivera, L.; Haessler, H.; Legrand, D.; Philip, H.; Dorbath, L.; McCormack, D.; Arefiev, S.; Langer, C.; Cisternas, A.

    1997-01-01

    The Racha-Dzhava earthquake (Ms = 7.0) that occurred on 1991 April 29 at 09:12:48.1 GMT in the southern border of the Great Caucasus is the biggest event ever recorded in the region, stronger than the Spitak earthquake (Ms = 6.9) of 1988. A field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity. A very precise image of the aftershock distribution is obtained, showing an elongated cloud oriented N105??, with one branch trending N310?? in the western part. The southernmost part extends over 80 km, with the depth ranging from 0 to 15 km, and dips north. The northern branch, which is about 30 km long, shows activity that ranges in depth from 5 to 15 km. The complex thrust dips northwards. A stress-tensor inversion from P-wave first-motion polarities shows a state of triaxial compression, with the major principal axis oriented roughly N-S, the minor principal axis being vertical. Body-waveform inversion of teleseismic seismograms was performed for the main shock, which can be divided into four subevents with a total rupture-time duration of 22 s. The most important part of the seismic moment was released by a gentle northerly dipping thrust. The model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks. The focal mechanisms of the three largest aftershocks were also inverted from body-wave records. The April 29th (Ms = 6.1) and May 5th (Ms = 5.4) aftershocks have thrust mechanisms on roughly E-W-oriented planes, similar to the main shock. Surprisingly, the June 15th (Ms = 6.2) aftershock shows a thrust fault striking N-S. This mechanism is explained by the structural control of the rupture along the east-dipping geometry of the Dzirula Massif close to the Borzhomi-Kazbeg strike-slip fault. In fact, the orientation and shape of the stress tensor produce a thrust on a N

  9. Seismic Noise Characterization in the Northern Mississippi Embayment

    NASA Astrophysics Data System (ADS)

    Wiley, S.; Deshon, H. R.; Boyd, O. S.

    2009-12-01

    We present a study of seismic noise sources present within the northern Mississippi embayment near the New Madrid Seismic Zone (NMSZ). The northern embayment contains up to 1 km of unconsolidated coastal plain sediments overlying bedrock, making it an inherently noisy environment for seismic stations. The area is known to display high levels of cultural noise caused by agricultural activity, passing cars, trains, etc. We characterize continuous broadband seismic noise data recorded for the months of March through June 2009 at six stations operated by the Cooperative New Madrid Seismic Network. We looked at a single horizontal component of data during nighttime hours, defined as 6:15PM to 5:45AM Central Standard Time, which we determined to be the lowest amplitude period of noise for the region. Hourly median amplitudes were compared to daily average wind speeds downloaded from the National Oceanic and Atmospheric Administration. We find a correlation between time periods of increased noise and days with high wind speeds, suggesting that wind is likely a prevalent source of seismic noise in the area. The effects of wind on seismic recordings may result from wind induced tree root movement which causes ground motion to be recorded at the vaults located ~3m below ground. Automated studies utilizing the local network or the EarthScope Transportable Array, scheduled to arrive in the area in 2010-11, should expect to encounter wind induced noise fluctuations and must account for this in their analysis.

  10. Single-station estimates of the seismic moment of the 1960 Chilean and 1964 Alaskan earthquakes, using the mantle magnitude M m

    NASA Astrophysics Data System (ADS)

    Okal, Emile A.; Talandier, Jacques

    1991-05-01

    Measurements are taken of the mantle magnitude M m , developed and introduced in previous papers, in the case of the 1960 Chilean and 1964 Alaskan earthquakes, by far the largest events ever recorded instrumentally. We show that the M m algorithm recovers the seismic moment of these gigantic earthquakes with an accuracy (typically 0.2 to 0.3 units of magnitude, or a factor of 1.5 to 2 on the seismic moment) comparable to that achieved on modern, digital, datasets. In particular, this study proves that the mantle magnitude M m does not saturate for large events, as do standard magnitude scales, but rather keeps growing with seismic moment, even for the very largest earthquakes. We further prove that the algorithm can be applied in unfavorable experimental conditions, such as instruments with poor response at mantle periods, seismograms clipped due to limited recording dynamics, or even on microbarograph records of air coupled Rayleigh waves. In addition, we show that it is feasible to use acoustic-gravity air waves generated by those very largest earthquakes, to obtain an estimate of the seismic moment of the event along the general philosophy of the magnitude concept: a single-station measurement ignoring the details of the earthquake's focal mechanism and exact depth.

  11. The data quality analyzer: a quality control program for seismic data

    USGS Publications Warehouse

    Ringler, Adam; Hagerty, M.T.; Holland, James F.; Gonzales, A.; Gee, Lind S.; Edwards, J.D.; Wilson, David; Baker, Adam

    2015-01-01

    The quantification of data quality is based on the evaluation of various metrics (e.g., timing quality, daily noise levels relative to long-term noise models, and comparisons between broadband data and event synthetics). Users may select which metrics contribute to the assessment and those metrics are aggregated into a “grade” for each station. The DQA is being actively used for station diagnostics and evaluation based on the completed metrics (availability, gap count, timing quality, deviation from a global noise model, deviation from a station noise model, coherence between co-located sensors, and comparison between broadband data and synthetics for earthquakes) on stations in the Global Seismographic Network and Advanced National Seismic System.

  12. Source spectra of seismic hum

    NASA Astrophysics Data System (ADS)

    Nishida, Kiwamu

    2014-10-01

    The observation of seismic hum from 2 to 20 mHz, also known as Earth's background free oscillations, has been established. Recent observations by broad-band seismometers show simultaneous excitation of Love waves (fundamental toroidal modes) and Rayleigh waves (fundamental spheroidal modes). The excitation amplitudes above 10 mHz can be explained by random shear traction sources on Earth's surface. With estimated source distributions, the most likely excitation mechanism is a linear coupling between ocean infragravity waves and seismic surface waves through seafloor topography. Observed Love and Rayleigh wave amplitudes below 5 mHz suggest that surface pressure sources could also contribute to their excitations, although the amplitudes have large uncertainties due to the high noise levels of the horizontal components. To quantify the observation, we develop a new method for estimation of the source spectra of random tractions on Earth's surface by modelling cross-spectra between pairs of stations. The method is to calculate synthetic cross-spectra for spatially isotropic and homogeneous excitations by random shear traction and pressure sources, and invert them with the observed cross-spectra to obtain the source spectra. We applied this method to the IRIS, ORFEUS, and F-net records from 618 stations with three components of broad-band seismometers for 2004-2011. The results show the dominance of shear traction above 5 mHz, which is consistent with past studies. Below 5 mHz, however, the spectral amplitudes of the pressure sources are comparable to those of shear traction. Observed acoustic resonance between the atmosphere and the solid Earth at 3.7 and 4.4 mHz suggests that atmospheric disturbances are responsible for the surface pressure sources, although non-linear ocean wave processes are also candidates for the pressure sources. Excitation mechanisms of seismic hum should be considered as a superposition of the processes of the solid Earth, atmosphere and ocean

  13. Leveraging EarthScope USArray with the Central and Eastern United States Seismic Network

    NASA Astrophysics Data System (ADS)

    Busby, R.; Sumy, D. F.; Woodward, R.; Frassetto, A.; Brudzinski, M.

    2015-12-01

    Recent earthquakes, such as the 2011 M5.8 Mineral, Virginia earthquake, raised awareness of the comparative lack of knowledge about seismicity, site response to ground shaking, and the basic geologic underpinnings in this densely populated region. With this in mind, the National Science Foundation, United States Geological Survey, United States Nuclear Regulatory Commission, and Department of Energy supported the creation of the Central and Eastern United States Seismic Network (CEUSN). These agencies, along with the IRIS Consortium who operates the network, recognized the unique opportunity to retain EarthScope Transportable Array (TA) seismic stations in this region beyond the standard deployment duration of two years per site. The CEUSN project supports 159 broadband TA stations, more than 30 with strong motion sensors added, that are scheduled to operate through 2017. Stations were prioritized in regions of elevated seismic hazard that have not been traditionally heavily monitored, such as the Charlevoix and Central Virginia Seismic Zones, and in regions proximal to nuclear power plants and other critical facilities. The stations (network code N4) transmit data in real time, with broadband and strong motion sensors sampling at 100 samples per second. More broadly the CEUSN concept also recognizes the existing backbone coverage of permanently operating seismometers in the CEUS, and forms a network of over 300 broadband stations. This multi-agency collaboration is motivated by the opportunity to use one facility to address multiple missions and needs in a way that is rarely possible, and to produce data that enables both researchers and federal agencies to better understand seismic hazard potential and associated seismic risks. In June 2015, the CEUSN Working Group (www.usarray.org/ceusn_working_group) was formed to review and provide advice to IRIS Management on the performance of the CEUSN as it relates to the target scientific goals and objectives. Map shows

  14. Investigation of Historic Seismic and Infrasound Records from Events Occurred at the Region of Novaya Zemplya Test Site by the USSR Stations

    NASA Astrophysics Data System (ADS)

    Sokolova, Inna

    2014-05-01

    Located in the north the Novaya Zemlya Test Site was used in Soviet time for conducting unique nuclear weapon tests in different mediums. 130 nuclear explosions with total yield 265 megatons were conducted at the Test Site for the period 1955-1990. During this period the following nuclear explosions were conducted: 1 surface explosion, 85 air explosions, 2 above water explosions, 3 underwater explosions and 39 underground explosions (in boreholes and tunnels). In addition, tectonic earthquakes and induced earthquakes caused by multi-megatons UNE occur near the Test Site. Unfortunately, only few seismic events occurred on the territory of the Test Site were recorded by digital stations. However, the archives of different seismological organizations of the USSR contain huge amount of analogue seismograms recorded by permanent and temporary stations. Historical seismograms of nuclear explosions and earthquakes from Novaya Zemlya Test site territory were digitized by the Complex Seismological Expedition IPE RAS and by the Institute of Geophysical Researches RK; a database of the events from the Test Site containing 470 seismograms at epicentral distance 2100-3800 was created. The database includes seismic records of air, underground nuclear explosions, and records of underwater nuclear explosion conducted within "Korall" exercise. In addition, infrasound records of waves from multi-megatons air nuclear explosions recorded by a microbarograph installed at Talgar seismic station at distance ~3600 km from the Test Site were digitized. Kinematic and dynamic parameters of nuclear explosions records conducted in different mediums (air, under water and underground) were investigated by the digitized records from events at Novaya Zemlya Test Site; specific features of wave pattern for each class of events were found.

  15. Seismic and deformation precursory to the small explosions of Marapi Volcano, West Sumatra, Indonesia

    NASA Astrophysics Data System (ADS)

    Hidayat, D.; Patria, C.; Gunawan, H.; Taisne, B.; Nurfiani, D.; Avila, E. J.

    2015-12-01

    Marapi Volcano is one of the active volcanoes of Indonesia located near the city of Bukittinggi, West Sumatra, Indonesia. Its activity is characterized by small vulcanian explosions with occasional VEI 2 producing tephra and pyroclastic flows. Due to its activity, it is being monitored by Centre for Volcanology and Geological Hazard Mitigation (CVGHM). Four seismic stations consists of 2 broadband and 2 short period instruments have been established since 2009. In collaboration with CVGHM, Earth Observatory of Singapore added 5 seismic stations around the volcano in 2014, initially with short period instruments but later upgraded to broadbands. We added one tilt station at the summit of Marapi. These seismic and tilt stations are telemetered by 5.8GHz radio to Marapi Observatory Post where data are archived and displayed for Marapi observers for their daily volcanic activity monitoring work. We also archive the data in the EOS and CVGHM main offices. Here we are presenting examples of seismic and deformation data from Marapi prior, during, and after the vulcanian explosion. Our study attempt to understand the state of the volcano based on monitoring data and in order to enable us to better estimate the hazards associated with the future eruptions of this or similar volcano.

  16. The Italian National Seismic Network

    NASA Astrophysics Data System (ADS)

    Michelini, Alberto

    2016-04-01

    The Italian National Seismic Network is composed by about 400 stations, mainly broadband, installed in the Country and in the surrounding regions. About 110 stations feature also collocated strong motion instruments. The Centro Nazionale Terremoti, (National Earthquake Center), CNT, has installed and operates most of these stations, although a considerable number of stations contributing to the INGV surveillance has been installed and is maintained by other INGV sections (Napoli, Catania, Bologna, Milano) or even other Italian or European Institutions. The important technological upgrades carried out in the last years has allowed for significant improvements of the seismic monitoring of Italy and of the Euro-Mediterranean Countries. The adopted data transmission systems include satellite, wireless connections and wired lines. The Seedlink protocol has been adopted for data transmission. INGV is a primary node of EIDA (European Integrated Data Archive) for archiving and distributing, continuous, quality checked data. The data acquisition system was designed to accomplish, in near-real-time, automatic earthquake detection and hypocenter and magnitude determination (moment tensors, shake maps, etc.). Database archiving of all parametric results are closely linked to the existing procedures of the INGV seismic monitoring environment. Overall, the Italian earthquake surveillance service provides, in quasi real-time, hypocenter parameters which are then revised routinely by the analysts of the Bollettino Sismico Nazionale. The results are published on the web page http://cnt.rm.ingv.it/ and are publicly available to both the scientific community and the the general public. This presentation will describe the various activities and resulting products of the Centro Nazionale Terremoti. spanning from data acquisition to archiving, distribution and specialised products.

  17. Determination of Rayleigh wave ellipticity across the Earthscope Transportable Array using single-station and array-based processing of ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Workman, Eli; Lin, Fan-Chi; Koper, Keith D.

    2016-10-01

    We present a single station method for the determination of Rayleigh wave ellipticity, or Rayleigh wave horizontal to vertical amplitude ratio (H/V) using Frequency Dependent Polarization Analysis (FDPA). This procedure uses singular value decomposition of 3-by-3 spectral covariance matrices over 1-hr time windows to determine properties of the ambient seismic noise field such as particle motion and dominant wave-type. In FPDA, if the noise is mostly dominated by a primary singular value and the phase difference is roughly 90° between the major horizontal axis and the vertical axis of the corresponding singular vector, we infer that Rayleigh waves are dominant and measure an H/V ratio for that hour and frequency bin. We perform this analysis for all available data from the Earthscope Transportable Array between 2004 and 2014. We compare the observed Rayleigh wave H/V ratios with those previously measured by multi-component, multi-station noise cross-correlation (NCC), as well as classical noise spectrum H/V ratio analysis (NSHV). At 8 sec the results from all three methods agree, suggesting that the ambient seismic noise field is Rayleigh wave dominated. Between 10 and 30 sec, while the general pattern agrees well, the results from FDPA and NSHV are persistently slightly higher (˜2%) and significantly higher (>20%), respectively, than results from the array-based NCC. This is likely caused by contamination from other wave types (i.e. Love waves, body waves, and tilt noise) in the single station methods, but it could also reflect a small, persistent error in NCC. Additionally, we find that the single station method has difficulty retrieving robust Rayleigh wave H/V ratios within major sedimentary basins, such as the Williston Basin and Mississippi Embayment, where the noise field is likely dominated by reverberating Love waves.

  18. Surface seismic measurements of near-surface P-and S-wave seismic velocities at earthquake recording stations, Seattle, Washington

    USGS Publications Warehouse

    Williams, R.A.; Stephenson, W.J.; Frankel, A.D.; Odum, J.K.

    1999-01-01

    We measured P-and S-wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured Vs correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average Vs in the upper 30 m (V??s30) of 150 to 170 m/s. These values of V??s30 place these sites in soil profile type E (V??s30 < 180 m/s). A "rock" site, located at Seward Park on Tertiary sedimentary deposits, has a V??S30 of 433 m/s, which is soil type C (V??s30: 360 to 760 m/s). The Seward Park site V??s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P-and S-wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S-wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

  19. Enhancing Seismic Monitoring Capability for Hydraulic Fracturing Induced Seismicity in Canada

    NASA Astrophysics Data System (ADS)

    Kao, H.; Cassidy, J. F.; Farahbod, A.; Lamontagne, M.

    2012-12-01

    The amount of natural gas produced from unconventional sources, such as the shale gas, has increased dramatically since the last decade. One of the key factors in the success of shale gas production is the application of hydraulic fracturing (also known as "fracking") to facilitate the efficient recovery of natural gas from shale matrices. As the fracking operation becomes routine in all major shale gas fields, its potential to induce local earthquakes at some locations has become a public concern. To address this concern, Natural Resources Canada has initiated a research effort to investigate the potential links between fracking operations and induced seismicity in some major shale gas basins of Canada. This federal-provincial collaborative research aims to assess if shale gas fracking can alter regional pattern of background seismicity and if so, what the relationship between how fracking is conducted and the maximum magnitude of induced seismicity would be. Other objectives include the investigation of the time scale of the interaction between fracking events and induced seismicity and the evaluation of induced seismicity potential for shale gas basins under different tectonic/geological conditions. The first phase of this research is to enhance the detection and monitoring capability for seismicity possibly related to shale gas recovery in Canada. Densification of the Canadian National Seismograph Network (CNSN) is currently underway in northeast British Columbia where fracking operations are taking place. Additional seismic stations are planned for major shale gas basins in other regions where fracking might be likely in the future. All newly established CNSN stations are equipped with broadband seismographs with real-time continuous data transmission. The design goal of the enhanced seismic network is to significantly lower the detection threshold such that the anticipated low-magnitude earthquakes that might be related to fracking operations can be

  20. Improving the Detectability of the Catalan Seismic Network for Local Seismic Activity Monitoring

    NASA Astrophysics Data System (ADS)

    Jara, Jose Antonio; Frontera, Tànit; Batlló, Josep; Goula, Xavier

    2016-04-01

    The seismic survey of the territory of Catalonia is mainly performed by the regional seismic network operated by the Cartographic and Geologic Institute of Catalonia (ICGC). After successive deployments and upgrades, the current network consists of 16 permanent stations equipped with 3 component broadband seismometers (STS2, STS2.5, CMG3ESP and CMG3T), 24 bits digitizers (Nanometrics Trident) and VSAT telemetry. Data are continuously sent in real-time via Hispasat 1D satellite to the ICGC datacenter in Barcelona. Additionally, data from other 10 stations of neighboring areas (Spain, France and Andorra) are continuously received since 2011 via Internet or VSAT, contributing both to detect and to locate events affecting the region. More than 300 local events with Ml ≥ 0.7 have been yearly detected and located in the region. Nevertheless, small magnitude earthquakes, especially those located in the south and south-west of Catalonia may still go undetected by the automatic detection system (DAS), based on Earthworm (USGS). Thus, in order to improve the detection and characterization of these missed events, one or two new stations should be installed. Before making the decision about where to install these new stations, the performance of each existing station is evaluated taking into account the fraction of detected events using the station records, compared to the total number of events in the catalogue, occurred during the station operation time from January 1, 2011 to December 31, 2014. These evaluations allow us to build an Event Detection Probability Map (EDPM), a required tool to simulate EDPMs resulting from different network topology scenarios depending on where these new stations are sited, and becoming essential for the decision-making process to increase and optimize the event detection probability of the seismic network.

  1. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    SciTech Connect

    Syuhada; Hananto, Nugroho D.; Handayani, Lina; Puspito, Nanang T; Yudistira, Tedi; Anggono, Titi

    2015-04-24

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  2. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    NASA Astrophysics Data System (ADS)

    Syuhada, Hananto, Nugroho D.; Puspito, Nanang T.; Anggono, Titi; Handayani, Lina; Yudistira, Tedi

    2015-04-01

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  3. Uncertainty estimates in broadband seismometer sensitivities using microseisms

    USGS Publications Warehouse

    Ringler, Adam T.; Storm, Tyler L.; Gee, Lind S.; Hutt, Charles R.; Wilson, David C.

    2015-01-01

    The midband sensitivity of a seismic instrument is one of the fundamental parameters used in published station metadata. Any errors in this value can compromise amplitude estimates in otherwise high-quality data. To estimate an upper bound in the uncertainty of the midband sensitivity for modern broadband instruments, we compare daily microseism (4- to 8-s period) amplitude ratios between the vertical components of colocated broadband sensors across the IRIS/USGS (network code IU) seismic network. We find that the mean of the 145,972 daily ratios used between 2002 and 2013 is 0.9895 with a standard deviation of 0.0231. This suggests that the ratio between instruments shows a small bias and considerable scatter. We also find that these ratios follow a standard normal distribution (R 2 = 0.95442), which suggests that the midband sensitivity of an instrument has an error of no greater than ±6 % with a 99 % confidence interval. This gives an upper bound on the precision to which we know the sensitivity of a fielded instrument.

  4. Seismic Ecology

    NASA Astrophysics Data System (ADS)

    Seleznev, V. S.; Soloviev, V. M.; Emanov, A. F.

    The paper is devoted to researches of influence of seismic actions for industrial and civil buildings and people. The seismic actions bring influence directly on the people (vibration actions, force shocks at earthquakes) or indirectly through various build- ings and the constructions and can be strong (be felt by people) and weak (be fixed by sensing devices). The great number of work is devoted to influence of violent seismic actions (first of all of earthquakes) on people and various constructions. This work is devoted to study weak, but long seismic actions on various buildings and people. There is a need to take into account seismic oscillations, acting on the territory, at construction of various buildings on urbanized territories. Essential influence, except for violent earthquakes, man-caused seismic actions: the explosions, seismic noise, emitted by plant facilities and moving transport, radiation from high-rise buildings and constructions under action of a wind, etc. can exert. Materials on increase of man- caused seismicity in a number of regions in Russia, which earlier were not seismic, are presented in the paper. Along with maps of seismic microzoning maps to be built indicating a variation of amplitude spectra of seismic noise within day, months, years. The presence of an information about amplitudes and frequencies of oscillations from possible earthquakes and man-caused oscillations in concrete regions allows carry- ing out soundly designing and construction of industrial and civil housing projects. The construction of buildings even in not seismically dangerous regions, which have one from resonance frequencies coincident on magnitude to frequency of oscillations, emitted in this place by man-caused objects, can end in failure of these buildings and heaviest consequences for the people. The practical examples of detail of engineering- seismological investigation of large industrial and civil housing projects of Siberia territory (hydro power

  5. Seismic monitoring at Deception Island volcano (Antarctica): Recent advances

    NASA Astrophysics Data System (ADS)

    Carmona, E.; Almendros, J.; Martín, R.; Cortés, G.; Alguacil, G.; Moreno, J.; Martín, B.; Martos, A.; Serrano, I.; Stich, D.; Ibáñez, J. M.

    2012-04-01

    Deception Island (South Shetland Island, Antarctica) is an active volcano with recent eruptions (e.g. 1967, 1969 and 1970). It is also among the Antarctic sites most visited by tourists. Besides, there are currently two scientific bases operating during the austral summers, usually from late November to early March. For these reasons it is necessary to deploy a volcano monitoring system as complete as possible, designed specifically to endure the extreme conditions of the volcanic environment and the Antarctic climate. The Instituto Andaluz de Geofísica of University of Granada, Spain (IAG-UGR) performs seismic monitoring on Deception Island since 1994 during austral summer surveys. The seismicity basically includes volcano-tectonic earthquakes, long-period events and volcanic tremor, among other signals. The level of seismicity is moderate, except for a seismo-volcanic crisis in 1999. The seismic monitoring system has evolved during these years, following the trends of the technological developments and software improvements. Recent advances have been mainly focused on: (1) the improvement of the seismic network introducing broadband stations and 24-bit data acquisition systems; (2) the development of a short-period seismic array, with a 12-channel, 24-bit data acquisition system; (3) the implementation of wireless data transmission from the network stations and also from the seismic array to a recording center, allowing for real-time monitoring; (4) the efficiency of the power supply systems and the monitoring of the battery levels and power consumption; (5) the optimization of data analysis procedures, including database management, automated event recognition tools for the identification and classification of seismo-volcanic signals, and apparent slowness vector estimates using seismic array data; (6) the deployment of permanent seismic stations and the transmission of data during the winter using a satellite connection. A single permanent station is operating

  6. Near-Real-Time Sismo-acoustic Submarine Station for offshore monitoring

    NASA Astrophysics Data System (ADS)

    D'Anna, Giuseppe; D'Alessandro, Antonino; Fertitta, Gioacchino; Fraticelli, Nicola; Calore, Daniele

    2016-04-01

    From the early 1980's, Italian seismicity is monitored by the National Seismic Network (NSN). The network has been considerably enhanced by INGV since 2005 by 24-bit digital stations equipped with broad-band sensors. The NSN is nowadays constituted by about 300 on-land seismic station able to detect and locate also small magnitude earthquake in the whole Italian peninsula. However, the lack of offshore seismic stations does not allow the accurate estimation of hypocentral and focal parameters of small magnitude earthquakes occurring in offshore areas. As in the Mediterranean area there is an intense offshore seismic activity, an extension of the seismic monitoring to the sea would be beneficial. There are two types of stations that could be used to extend the network towards the sea: the first type is connected to the coast though a cable, the second type is isolated (or stand alone) and works autonomously. Both solutions have serious limitations: the first one, for several technical and economic problems, linked to the indispensable transmission/alimentation cable, cannot be installed far from the coast; the second one, allows access to the recorded data, only after they are recovered from the seabed. It is clear that these technical solutions are not suitable for the real time monitoring of the offshore seismicity or for the realization of a tsunami warning system. For this reason, in early 2010, the OBSLab of Gibilmanna begins the design of a submarine station able to overcome the limitations of the two systems above. The station isbuilt under the project EMSO-MedIT. The two stations built have already been tested in dock and ready for installation. One of this station will be installed, in few time, in the southern Tyrrhenian Sea, near the epicentre of the Palermo 2002 main shock. The sea bottom station will be equipped with 2 very broadband 3C seismometers, a broad band hydrophone, a differential and an absolute pressure gauge. The station includes a submarine

  7. Observations and Modeling of Seismic Background Noise

    USGS Publications Warehouse

    Peterson, Jon R.

    1993-01-01

    INTRODUCTION The preparation of this report had two purposes. One was to present a catalog of seismic background noise spectra obtained from a worldwide network of seismograph stations. The other purpose was to refine and document models of seismic background noise that have been in use for several years. The second objective was, in fact, the principal reason that this study was initiated and influenced the procedures used in collecting and processing the data. With a single exception, all of the data used in this study were extracted from the digital data archive at the U.S. Geological Survey's Albuquerque Seismological Laboratory (ASL). This archive dates from 1972 when ASL first began deploying digital seismograph systems and collecting and distributing digital data under the sponsorship of the Defense Advanced Research Projects Agency (DARPA). There have been many changes and additions to the global seismograph networks during the past twenty years, but perhaps none as significant as the current deployment of very broadband seismographs by the U.S. Geological Survey (USGS) and the University of California San Diego (UCSD) under the scientific direction of the IRIS consortium. The new data acquisition systems have extended the bandwidth and resolution of seismic recording, and they utilize high-density recording media that permit the continuous recording of broadband data. The data improvements and continuous recording greatly benefit and simplify surveys of seismic background noise. Although there are many other sources of digital data, the ASL archive data were used almost exclusively because of accessibility and because the data systems and their calibration are well documented for the most part. Fortunately, the ASL archive contains high-quality data from other stations in addition to those deployed by the USGS. Included are data from UCSD IRIS/IDA stations, the Regional Seismic Test Network (RSTN) deployed by Sandia National Laboratories (SNL), and the

  8. The Central and Eastern U.S. Seismic Network: Legacy of USArray

    NASA Astrophysics Data System (ADS)

    Eakins, J. A.; Astiz, L.; Benz, H.; Busby, R. W.; Hafner, K.; Reyes, J. C.; Sharer, G.; Vernon, F.; Woodward, R.

    2014-12-01

    As the USArray Transportable Array entered the central and eastern United States, several Federal agencies (National Science Foundation, U.S. Geological Survey, U.S. Nuclear Regulatory Commission, and Department of Energy) recognized the unique opportunity to retain TA stations beyond the original timeline. The mission of the CEUSN is to produce data that enables researchers and Federal agencies alike to better understand the basic geologic questions, background earthquake rates and distribution, seismic hazard potential, and associated societal risks of this region. The selected long-term sub-array from Transportable Array (TA) stations includes nearly 200 sites, complemented by 100 broadband stations from the existing regional seismic networks to form the Central and Eastern United States Network (CEUSN). Multiple criteria for site selection were weighed by an inter-agency TA Station Selection (TASS) Working Group: seismic noise characteristics, data availability in real time, proximity to nuclear power plants, and homogeneous distribution throughout the region. The Array Network Facility (ANF) started collecting data for CEUSN network stations since late 2013, with all stations collected since May 2014. Regional seismic data streams are collected in real-time from the IRIS Data Management Center (DMC). TA stations selected to be part of CEUSN, retain the broadband sensor to which a 100 sps channel is added, the infrasound and environmental channels, and, at some stations, accelerometers are deployed. The upgraded sites become part of the N4 network for which ANF provides metadata and can issue remote commands to the station equipment. Stations still operated by TA, but planned for CEUSN, are included in the virtual network so all stations are currently available now. By the end of 2015, the remaining TA stations will be upgraded. Data quality control procedures developed for TA stations at ANF and at the DMC are currently performed on N4 data. However

  9. Discriminating non-seismic long-period pulses and noise to improve earthquake source inversion

    NASA Astrophysics Data System (ADS)

    Sakai, Takahide; Kumagai, Hiroyuki; Pulido, Nelson; Bonita, Jun; Nakano, Masaru

    2016-04-01

    Broadband seismometers produce artifacts resembling long-period pulses (non-seismic pulses) that degrade centroid moment tensor (CMT) estimations based on waveform inversion of broadband seismic records in long-period bands (50-200 s). We propose a method to discriminate non-seismic pulses and long-period noise from seismic signals, which can be applied to automatic CMT inversion analysis. In this method, we calculate source amplitudes as peak-to-peak displacement amplitudes in individual long-period seismic records after each event has been corrected for medium attenuation and geometric spreading and then estimate the ratios of individual source amplitudes to the minimum source amplitude. Because source amplitude ratios for non-seismic pulses tend to be greater than those of the seismic signals, we use seismic records in CMT estimations only if their source amplitude ratios are lower than a threshold value ( R). We tested this method using broadband seismic data from the Philippines and found that reprocessed inversion solutions using this method showed a clear improvement when using R = 11, although focal mechanism estimations were not entirely stable. To investigate the general applicability of this method, we analyzed broadband seismic data from F-net in Japan. Our analysis indicated that source amplitude ratios in F-net data ranged up to about 20, indicating that the threshold value may be dependent on station density. Given that F-net is one of the highest density networks in the world, we may assume that a threshold value between 10 and 20 is appropriate for application of our method for most regional broadband networks. Our synthetic tests indicated that source amplitude ratios can be as high as 103, although observed ratios are only within the range 10-20. This suggests that we happened to observe only events having focal mechanisms with source amplitude ratios of 10-20. Alternatively, these high source amplitude ratios can be explained by distortion of

  10. The LUSI Seismic Experiment: Deployment of a Seismic Network around LUSI, East Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Karyono, Karyono; Mazzini, Adriano; Lupi, Matteo; Syafri, Ildrem; Haryanto, Iyan; Masturyono, Masturyono; Hadi, Soffian; Rohadi, Suprianto; Suardi, Iman; Rudiyanto, Ariska; Pranata, Bayu

    2015-04-01

    The spectacular Lusi eruption started in northeast Java, Indonesia the 29 of May 2006 following a M6.3 earthquake striking the island. Initially, several gas and mud eruption sites appeared along the reactivated strike-slip Watukosek fault system and within weeks several villages were submerged by boiling mud. The most prominent eruption site was named Lusi. Lusi is located few kilometres to the NE of the Arjuno-Welirang volcanic complex. Lusi sits upon the Watukosek fault system. From this volcanic complex originates the Watukosek fault system that was reactivated by the M6.3 earthquake in 2006 and is still periodically reactivated by the frequent seismicity. To date Lusi is still active and erupting gas, water, mud and clasts. Gas and water data show that the Lusi plumbing system is connected with the neighbouring Arjuno-Welirang volcanic complex. This makes the Lusi eruption a "sedimentary hosted geothermal system". To verify and characterise the occurrence of seismic activity and how this perturbs the connected Watukosek fault, the Arjuno-Welirang volcanic system and the ongoing Lusi eruption, we deployed 30 seismic stations (short-period and broadband) in this region of the East Java basin. The seismic stations are more densely distributed around LUSI and the Watukosek fault zone that stretches between Lusi and the Arjuno Welirang (AW) complex. Fewer stations are positioned around the volcanic arc. Our study sheds light on the seismic activity along the Watukosek fault system and describes the waveforms associated to the geysering activity of Lusi. The initial network aims to locate small event that may not be captured by the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) seismic network and it will be crucial to design the second phase of the seismic experiment that will consist of a local earthquake tomography of the Lusi-Arjuno Welirang region and temporal variations of vp/vs ratios. Such variations will then be ideally related to

  11. Seismic imaging of esker structures from a combination of high-resolution broadband multicomponent streamer and wireless sensors, Turku-Finland

    NASA Astrophysics Data System (ADS)

    Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti; Malehmir, Alireza

    2015-04-01

    Eskers and glaciofluvial interlobate formations, mainly composed of sands and gravels and deposited in winding ridges, define the locations of glacial melt-water streams. These sediments, porous and permeable, form the most important aquifers in Finland and are often used as aggregates or for artificial aquifer recharge. The Virttaankangas interlobate suite and artificial aquifer recharge plant provides the entire water supply for the city of Turku and therefore an accurate delineation of the aquifer is critical for long term planning and sustainable use of these natural resources. The study area is part of the Säkylänharju-Virttaankangas Glaciofluvial esker-chain complex and lies on an igneous, crystalline basement rocks. To provide complementary information to existing boreholes and GPR studies at the site, such as identification of potential esker cores, planning for a water extraction, fractured bedrock and possible kettle holes, a new seismic investigation was designed and carried out during summer 2014. Two seismic profiles each about 1 km long were acquired using a newly developed 200 m long prototype, comprising of 80-3C MEMs-based, landstreamer system. To provide velocity information at larger depths (and longer offsets), fifty-two 10-Hz 1C wireless sensors spaced at about every 20 m were used. A Bobcat mounted drop-hammer source, generating three hits per source location, was used as the seismic source. This proved to be a good choice given the attenuative nature of the dry sediments down to about 20 m depth. One of the seismic lines overlaps an existing streamer survey and thus allows a comparison between the system used in this study and the one employed before. Except at a few places where the loose sands mixed with leaves affected the coupling, the data quality is excellent with several reflections identifiable in the raw shot gathers. First arrivals were easily identifiable in almost all the traces and shots and this allowed obtaining velocity

  12. Broadband network on-line data acquisition system with web based interface for control and basic analysis

    NASA Astrophysics Data System (ADS)

    Polkowski, Marcin; Grad, Marek

    2016-04-01

    Passive seismic experiment "13BB Star" is operated since mid 2013 in northern Poland and consists of 13 broadband seismic stations. One of the elements of this experiment is dedicated on-line data acquisition system comprised of both client (station) side and server side modules with web based interface that allows monitoring of network status and provides tools for preliminary data analysis. Station side is controlled by ARM Linux board that is programmed to maintain 3G/EDGE internet connection, receive data from digitizer, send data do central server among with additional auxiliary parameters like temperatures, voltages and electric current measurements. Station side is controlled by set of easy to install PHP scripts. Data is transmitted securely over SSH protocol to central server. Central server is a dedicated Linux based machine. Its duty is receiving and processing all data from all stations including auxiliary parameters. Server side software is written in PHP and Python. Additionally, it allows remote station configuration and provides web based interface for user friendly interaction. All collected data can be displayed for each day and station. It also allows manual creation of event oriented plots with different filtering abilities and provides numerous status and statistic information. Our solution is very flexible and easy to modify. In this presentation we would like to share our solution and experience. National Science Centre Poland provided financial support for this work via NCN grant DEC-2011/02/A/ST10/00284.

  13. Usability of ocean-bottom seismograms for broadband waveform tomography

    NASA Astrophysics Data System (ADS)

    Eibl, Eva P. S.; Sigloch, Karin

    2013-04-01

    eight frequency passbands and on the broadband waveform, after careful correction for source parameters and source time function (Sigloch and Nolet 2006). As expected, permanent continental stations were quieter than permanent island stations in the Pacific, (independent of frequency band), and island stations were quieter than ocean-bottom stations. Relative data quality for both types of oceanic stations is lowest for dominant periods between 11s and 3 s. We present statistics for the fraction of usable data, as a function of station type, frequency band, and sensor type. In the lowest frequency band 55%, 71% and 90% of the data recorded by the PLUME stations, island stations and land stations, respectively, can be used for seismic tomography. These values drop with increasing frequency, to a minimum of 12% for the island stations, 8% for OBS stations and 33% for the land stations. We also compare data quality by OBS sensor type (Nanometrics T-40, Nanometrics T-240, Güralp CMG-3T). We find that frequency bands around 2.7 s and between 20.0 to 30.0 s have low noise levels but have not been used for tomography by the project PIs. A multiple-frequency waveform inversion including these additional bands and wave paths, as well as a larger number of earthquakes (101 versus 97 and 59 used in the original studies by Wolfe et al. 2009 and Wolfe et al. 2011) should be able to improve the resolution of the velocity structure in the upper and lower mantle beneath the Hawaiian hotspot. References: Laske, G., Collins, J. A., Wolfe, C. J., Solomon, S. C., Detrick, R. S., Orcutt, J. A., Bercovici, D., Hauri, E. H. (2009). Probing the Hawaiian hotspot with new broadband ocean bottom instruments. Eos Trans. AGU, 90(41), 362-363. Sigloch, K., & Nolet, G. (2006). Measuring finite-frequency body-wave amplitudes and traveltimes. Geophysical Journal International, 167(1), 271-287, doi:10.1111/j.1365-246X.2006.03116.x Wolfe, C.J, Solomon, S.C., Laske G., Collins, J.A., Detrick, R

  14. Calibration of seismic wave propagation in Jordan

    SciTech Connect

    Al-Husien, A; Amrat, A; Harris, D; Mayeda, K; Nakanishi, K; Rodgers, A; Ruppert, S; Ryall, F; Skinnell, K; Yazjeen, T

    1999-07-23

    The Natural Resources Authority of Jordan (NRA), the USGS and LLNL have a collaborative project to improve the calibration of seismic propagation in Jordan and surrounding regions. This project serves common goals of CTBT calibration and earthquake hazard assessment in the region. These objectives include accurate location of local and regional earthquakes, calibration of magnitude scales, and the development of local and regional propagation models. In the CTBT context, better propagation models and more accurately located events in the Dead Sea rift region can serve as (potentially GT5) calibration events for generating IMS location corrections. The detection and collection of mining explosions underpins discrimination research. The principal activity of this project is the deployment of two broadband stations at Hittiyah (south Jordan) and Ruweishid (east Jordan). These stations provide additional paths in the region to constrain structure with surface wave and body wave tomography. The Ruweishid station is favorably placed to provide constraints on Arabian platform structure. Waveform modeling with long-period observations of larger earthquakes will provide constraints on 1-D velocity models of the crust and upper mantle. Data from these stations combined with phase observations from the 26 short-period stations of the Jordan National Seismic Network (JNSN) may allow the construction of a more detailed velocity model of Jordan. The Hittiyah station is an excellent source of ground truth information for the six phosphate mines of southern Jordan and Israel. Observations of mining explosions collected by this station have numerous uses: for definition of templates for screening mining explosions, as ground truth events for calibrating travel-time models, and as explosion populations in development and testing discriminants. Following previously established procedures for identifying explosions, we have identified more than 200 explosions from the first 85 days of

  15. New Observations of Seismic Group Velocities in the Western Solomon Islands from Cross-Correlation of Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Ku, C. S.; You, S. H.; Kuo, Y. T.; Huang, B. S.; Wu, Y. M.; Chen, Y. G.; Taylor, F. W.

    2015-12-01

    A MW 8.1 earthquake occurred on 1 April 2007 in the western Solomon Islands. Following this event, a damaging tsunami was induced and hit the Island Gizo where the capital city of Western Province of Solomon Islands located. Several buildings of this city were destroyed and several peoples lost their lives during this earthquake. However, during this earthquake, no near source seismic instrument has been installed in this region. The seismic evaluations for the aftershock sequence, the possible earthquake early warning and tsunami warning were unavailable. For the purpose of knowing more detailed information about seismic activity in this region, we have installed 9 seismic stations (with Trillium 120PA broadband seismometer and Q330S 24bit digitizer) around the rupture zone of the 2007 earthquake since September of 2009. Within a decade, it has been demonstrated both theoretically and experimentally that the Green's function or impulse response between two seismic stations can be retrieved from the cross-correlation of ambient noise. In this study, 6 stations' observations which are more complete during 2011/10 ~ 2012/12 period, were selected for the purpose of the cross-correlation analysis of ambient seismic noise. The group velocities at period 2-20 seconds of 15 station-pairs were extracted by using multiple filter technique (MFT) method. The analyzed results of this study presented significant results of group velocities with higher frequency contents than other studies (20-60 seconds in usually cases) and opened new opportunities to study the shallow crustal structure of the western Solomon Islands.

  16. Geologic interpretation of seismic data relocation Route 2, Littleton Road grade separation stations 243-252 in Harvard, Mass.

    USGS Publications Warehouse

    May, James E.; Linehan, Rev. Daniel

    1950-01-01

    During parts of June and July 1949 nine seismic traverses were made at this site. Upon preliminary office development, the velocity data for some of these traverses were though to be inadequate and it was recommended that these lines be re-surveyed. Later surveys (March 1950), however, of nearby sites indicated that the original data were reliable and that a re-survey was unnecessary. The work was done as part of a cooperative program of the Massachusetts Department of Public Works and the United States Geological Survey.

  17. Tilt signals derived from a GEOSCOPE VBB Station on the Piton de la Fournaise Volcano

    NASA Astrophysics Data System (ADS)

    Battaglia, Jean; Aki, Keiiti; Montagner, J.-P.

    2000-03-01

    We report some very long period transients observed on a very broadband seismic station of the GEOSCOPE network, which is situated 8 km away from the summit of the Piton de la Fournaise volcano. We transform the ground velocity measured by the seismic station into tilt and test the result by comparing with data from Blum-type classical pendulum tiltmeters located in the same vault. The comparison validates the use of the horizontal seismometers for measuring tilt for periods shorter than 25 hours. The method is applied to the transients observed prior to several eruptions and magmatic intrusions since 1991. Because of the moderate distance between GEOSCOPE station and the summit of the volcano, the obtained tilt measurements provide information about eruptions and intrusions which complement the information on the geometry and location of the magmatic source provided by the summit tilt network.

  18. Local seismic events in area of Poland based on data from PASSEQ 2006-2008 experiment

    NASA Astrophysics Data System (ADS)

    Polkowski, Marcin; Plesiewicz, Beata; Wiszniowski, Jan; Wilde-Piórko, Monika; Passeq Working Group

    2014-05-01

    PASSEQ 2006-2008 (Passive Seismic Experiment in TESZ; Wilde-Piórko et al, 2008) was the biggest so far passive seismic experiment in the area of Central Europe (Poland, Germany, Czech Republic and Lithuania). 196 seismic stations (including 49 broadband seismometers) worked simultaneously for over two years. During experiment multiple types of data recorders and seismometers were used making analysis more complex and time consuming. Dataset was unified and repaired to start the detection of local seismic events. Two different approaches for detection were applied for stations located in Poland. One used standard STA/LTA triggers (Carl Johnson's STA/LTA algorithm) and grid search to classify and locate events. Result was manually verified. Other approach used Real Time Recurrent Network (RTRN) detection (Wiszniowski et al, 2014). Both methods gave similar results showing four previously unknown seismic events located in area of Gulf Of Gdańsk in southern Baltic Sea. The investigation of local seismicity is a good opportunity for verification of new seismic models of lithosphere in the area. In this paper we discuss both detection methods with their pros and cons (accuracy, efficiency, manual work required, scalability). We also show details of all detected and previously unknown events in discussed area. This work was partially supported by NCN grant UMO-2011/01/B/ST10/06653.

  19. Seismic excitation by the space shuttle Columbia

    USGS Publications Warehouse

    Kanamori, H.; Mori, J.; Anderson, D.L.; Heaton, T.H.

    1991-01-01

    SEISMIC stations in southern California recorded the atmospheric shock waves generated by the space shuttle Columbia on its return to the Edwards Air Force base on 13 August 1989 (Fig. 1). In addition to the shock wave, the broad-band IRIS-TERRAscope station at Pasadena recorded a distinct pulse with a period of ???2-3 seconds, which arrived 12.5 seconds before the shock wave (Fig. 2). This pulse was also recorded at the University of Southern California, near downtown Los Angeles, where it arrived 3 seconds after the shock wave. The origin of this pulse could not be readily identified. We show here that it was a seismic P wave excited by the motion of high-rise buildings in downtown Los Angeles, which were hit by the shock wave. The proximity of the natural period of the high-rise buildings to that of the Los Angeles basin enabled efficient energy transfer from shock wave to seismic wave.

  20. The seismic project of the National Tsunami Hazard Mitigation Program

    USGS Publications Warehouse

    Oppenheimer, D.H.; Bittenbinder, A.N.; Bogaert, B.M.; Buland, R.P.; Dietz, L.D.; Hansen, R.A.; Malone, S.D.; McCreery, C.S.; Sokolowski, T.J.; Whitmore, P.M.; Weaver, C.S.

    2005-01-01

    In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years. ?? Springer 2005.

  1. Measurement of the Parameter Kappa, and Reevaluation of Kappa for Small to Moderate Earthquakes at Seismic Stations in the Vicinity of Yucca Mountain, Nevada

    SciTech Connect

    Biasi, Glenn; Anderson, John G

    2007-12-05

    The parameter kappa was defined by Anderson and Hough (1984) to describe the high-frequency spectral roll-off of the strong motion seismic spectrum. In the work of Su et al., (1996) the numerical value of kappa estimated for sites near Yucca Mountain was small (~20 ms). The estimate obtained from these events has been applied through a rigorous methodology to develop design earthquake spectra with magnitude over 5.0. Smaller values of kappa lead to higher estimated ground motions in the methodology used by the Probabilistic Seismic Hazard Analysis (PSHA) for Yucca Mountain. An increase of 10 ms in kappa could result in a substantial decrease in the high frequency level of the predicted ground motions. Any parameter that plays such a critical role deserves close examination. Here, we study kappa and its associated uncertainties. The data set used by Su et al (1996) consisted of 12 M 2.8 to 4.5 earthquakes recorded at temporary stations deployed after the June 1992 Little Skull Mountain earthquake. The kappa elements of that study were revisited by Anderson and Su (MOL.20071203.0134) and substantially confirmed. One weakness of those studies is the limited data used. Few of these stations were on tuff or on Yucca Mountain itself. A decade of Southern Great Basin Digital Seismic Network (SGBDSN) recording has now yielded a larger body of on-scale, well calibrated digital ground motion records suitable for investigating kappa. We use the SGBDSN data to check some of the original assumptions, improve the statistical confidence of the conclusions, and determine values of kappa for stations on or near Yucca Mountain. The outstanding issues in kappa analysis, as they apply to Yucca Mountain, include: 1. The number itself. The kappa estimate near 20 msec from Su et al. (1996) and Anderson and Su (MOL.20071203.0134) is markedly smaller than is considered typical in California (Silva, 1995). The low kappa value has engineering consequences because when it is applied in ground

  2. Deployment of a Long-Term Broadband Seafloor Observatory in Monterey Bay

    NASA Astrophysics Data System (ADS)

    McGill, P.; Neuhauser, D.; Stakes, D.; Romanowicz, B.; Ramirez, T.; Uhrhammer, R.

    2002-12-01

    MOBB (Monterey bay Ocean floor Broad Band project) is a collaborative project between the Monterey Bay Aquarium Research Institute (MBARI) and the Berkeley Seismological Laboratory (BSL). Its goal is to install and operate a permanent seafloor broadband seismic station as a first step towards extending the on-shore broadband seismic network in northern California to the seaside of the North-America/Pacific plate boundary, providing better azimuthal coverage for regional earthquake and structure studies. The successful MOBB deployment took place 40km off shore at a water depth of 1000m during three dives on April 9-11, 2002. The seismometer was buried in a 60-cm deep caisson, which was later back filled with glass beads to stabilize the instrument. New tools, including a high-pressure water-jet excavator, were developed for the ROV Ventana to accomplish these tasks. The ocean-bottom MOBB station currently comprises a three-component seismometer package, a current-meter, and a recording and battery package. Data recovery dives, during which the recording and battery package will be exchanged, are planned every three months for the next three years. A differential pressure gauge (DPG) (Cox et al., 1984) will be deployed as part of the recording package during the next data recovery dive in September 2002. The station is currently recording data autonomously. Eventually, it will be linked to the planned (and recently funded) MARS (Monterey Accelerated Research System; rl {http://www.mbari.org/mars/}) cable and provide real-time, continuous seismic data to be merged with the rest of the northern California real-time seismic system. The data are archived at the NCEDC for on-line availability, as part of the Berkeley Digital Seismic Network (BDSN). This project follows the 1997 MOISE experiment, in which a three-component broadband system was deployed for a period of three months, 40km off shore in Monterey Bay. MOISE was a cooperative program sponsored by MBARI, UC

  3. Development of XML Schema for Broadband Digital Seismograms and Data Center Portal

    NASA Astrophysics Data System (ADS)

    Takeuchi, N.; Tsuboi, S.; Ishihara, Y.; Nagao, H.; Yamagishi, Y.; Watanabe, T.; Yanaka, H.; Yamaji, H.

    2008-12-01

    There are a number of data centers around the globe, where the digital broadband seismograms are opened to researchers. Those centers use their own user interfaces and there are no standard to access and retrieve seismograms from different data centers using unified interface. One of the emergent technologies to realize unified user interface for different data centers is the concept of WebService and WebService portal. Here we have developed a prototype of data center portal for digital broadband seismograms. This WebService portal uses WSDL (Web Services Description Language) to accommodate differences among the different data centers. By using the WSDL, alteration and addition of data center user interfaces can be easily managed. This portal, called NINJA Portal, assumes three WebServices: (1) database Query service, (2) Seismic event data request service, and (3) Seismic continuous data request service. Current system supports both station search of database Query service and seismic continuous data request service. Data centers supported by this NINJA portal will be OHP data center in ERI and Pacific21 data center in IFREE/JAMSTEC in the beginning. We have developed metadata standard for seismological data based on QuakeML for parametric data, which has been developed by ETH Zurich, and XML-SEED for waveform data, which was developed by IFREE/JAMSTEC. The prototype of NINJA portal is now released through IFREE web page (http://www.jamstec.go.jp/pacific21/).

  4. Dynamic Bayesian filtering for real-time seismic analyses

    SciTech Connect

    Blough, D.K.; Rohay, A.C.; Anderson, K.K.; Nicholson, W.L.

    1994-04-01

    State space modeling, which includes techniques such as the Kalman filter, has been used to analyze many non-stationary time series. The ability of these dynamic models to adapt and track changes in the underlying process makes them attractive for application to the real-time analysis of three-component seismic waveforms. The authors are investigating the application of state space models formulated as Bayesian time series models to phase detection, polarization, and spectrogram estimation of seismograms. This approach removes the need to specify data windows in the time series for time averaging estimation (e.g., spectrum estimation). They are using this model to isolate particular seismic phases based on polarization parameters that are determined at a spectrum of frequencies. They plan to use polarization parameters, frequency spectra, and magnitudes to discriminate between different types of seismic sources. They present the application of this technique to artificial time series and to several real seismic events including the Non-Proliferation Experiment (NPE) two nuclear tests and three earthquakes from the Nevada Test site, as recorded on several regional broadband seismic stations. A preliminary result of this analysis indicates that earthquakes and explosions can potentially be discriminated on the bass of the polarization characteristics of scattered seismic phases. However, the chemical (NPE) and nuclear explosions appear to have very similar polarization characteristics.

  5. Predicting Strong Motions for Seismic Hazard Assessments in Seattle, Washington

    NASA Astrophysics Data System (ADS)

    Delorey, Andrew A.

    Much of Seattle, Washington lies atop a deep sedimentary basin. The Seattle Basin amplifies and distorts seismic waves in ways that modulate the hazard from earthquakes. Seismic hazard assessments heavily depend upon upper crustal and near-surface S-wave velocity models, which have traditionally been constructed from P-wave models using an empirical relationship between P-wave and S-wave velocity or by interpolating and extrapolating widely spaced observations of shallow geologic structures. Improving the accuracy and resolution of basin S-wave models is key to predictions for ground shaking. Tomography, with short-period Rayleigh waves extracted using noise interferometry, can refine S-wave velocity models in urban areas with dense arrays of short-period and broadband instruments. I apply this technique to the Seattle area to develop a new shallow S-wave model for use in hazard assessment. Continuous data from the Seismic Hazards in Puget Sound (SHIPS) array and local broadband stations have inter-station distances as short as a few kilometers. This spacing allows me to extract Rayleigh waves between 2-10s period that are sensitive to shallow basin structure. My results reveal greater detail in the upper 4 km than previous models. I use the new model to make predictions on the levels of ground motions for a variety of representative crustal and Benioff Zone earthquakes. My simulations reveal additional risk from earthquake shaking in some neighborhoods in north Seattle from crustal events relative to predictions made in the current seismic hazard map. The predicted amplitudes in the Seattle neighborhoods of Capital Hill and Queen Anne are twice as high as previous predictions for some events. The combined risk for all possible events will increase somewhat due to these predictions. My simulations of Benioff Zone events show similar results to the previous model used to make predictions for the seismic hazard map.

  6. Establishing seismic network capabilities in Haïti

    NASA Astrophysics Data System (ADS)

    Clouard, Valerie; Saurel, Jean-Marie; Prepetit, Claude; McNamara, Daniel; Hough, Susan; Saint-Louis, Mildor; Altidor, Jean-Robert

    2014-05-01

    The January 12, 2010 earthquake ruptured a poorly instrumented region that is located on a complex, wide, deformed zone on the boundary between the Caribbean Plate and the North American Plate. This event evidenced the need for a permanent seismic network in Haiti. Immediately after the 2010 earthquake, a strong motion network was deployed by USGS and 3 broadband seismometers were installed by the NRCAN. All this instrumentation is still working, however, it is mainly located around Port-au-Prince. In 2011, the UTS (Technical Unit of Seismology) was created by the BME (Mining and Energy Bureau) to take in charge the seismic monitoring of the national territory and a Memorandum of Understanding was signed with IPGP that would help through its Antilles Volcano and Seismic Observatories. After a 2-month training in Martinique of Haitian operators, Earthworm and Seiscomp3 were installed on the UTS server and neighboring country stations were include to the detection network. To enlarge the seismic networks to the whole territory, 10 broadband seismometers and 6 accelerometers were acquired. With these new stations, which will be installed in 2014 in secured places equipped with internet or VSAT antenna and with network code AY, the seismic performance standards for the detection and analysis of earthquakes change: 1) Earthquake detection from 30 seconds to 10, 2) Minimum magnitude threshold from M3.8 to M2.8, and 3) Initial hypocenter error from 5km to less than 2 km. The remaining efforts should focus on permanent and qualified human resources to maintain these networks.

  7. The new Algerian Digital Seismic Network (ADSN): towards an earthquake early-warning system

    NASA Astrophysics Data System (ADS)

    Yelles-Chaouche, A.; Allili, T.; Alili, A.; Messemen, W.; Beldjoudi, H.; Semmane, F.; Kherroubi, A.; Djellit, H.; Larbes, Y.; Haned, S.; Deramchi, A.; Amrani, A.; Chouiref, A.; Chaoui, F.; Khellaf, K.; Nait Sidi Said, C.

    2013-10-01

    Seismic monitoring in Algeria has seen great changes since the Boumerdes earthquake of 21 May 2003. Indeed, the installation of a new digital seismic network has resulted in a significant upgrade of the previous analog telemetry network. During the last four years, the number of stations in operation has increased substantially from 25 to 69, and 20 of these are broadband, 2 are very broadband, 47 are short period. 21 are equipped with accelerometers. They are all managed by Antelope software from Kinemetrics (US Cie), and they are all connected in real time and use various modes of transmission (e.g., satellite, internet, mobile phone). The spatial repartition of the stations now cover most of northern Algeria. In addition, 70 GPS stations have recently been added to this seismological network, most of them collocated with the seismological stations. Since the installation of the network, the records of local or distant events have improved significantly. The automatic processing of the data in a few minutes allows alert messages to be distributed to Civil Defense and other national authorities to react promptly to any emergency. The current strategy is to improve the data quality, to increase the density of the network by adding about 50 new stations, to reduce the processing time, and to reduce the time needed to send out an alert message. The result should be greatly improved network performance, which will lead to an effective early-warning system.

  8. Rupture directivity of the major shocks in the 1997 Umbria-Marche (central Italy) sequence from regional broadband waveforms

    NASA Astrophysics Data System (ADS)

    Alessandro Pino, Nicola; Mazza, Salvatore; Boschi, Enzo

    1999-07-01

    We derive the relative moment rate function for the main shocks in the Fall 1997 Central Italy seismic sequence (Mw=5.7; 6.0; 5.6) by applying an empirical Green function method. By using three conveniently placed broad-band MedNet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes, with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one. Taking a simple source model, forward modeling is utilized for determining fault parameters such as length, rupture propagation velocity and direction and slip distribution.

  9. Long-term changes of the glacial seismicity: case study from Spitsbergen

    NASA Astrophysics Data System (ADS)

    Gajek, Wojciech; Trojanowski, Jacek; Malinowski, Michał

    2016-04-01

    Changes in global temperature balance have proved to have a major impact on the cryosphere, and therefore withdrawing glaciers are the symbol of the warming climate. Our study focuses on year-to-year changes in glacier-generated seismicity. We have processed 7-year long continuous seismological data recorded by the HSP broadband station located in the proximity of Hansbreen glacier (Hornsund, southern Spitsbergen), obtaining seismic activity distribution between 2008 and 2014. We developed a new fuzzy logic algorithm to distinguish between glacier- and non-glacier-origin events. The algorithm takes into account the frequency of seismic signal and the energy flow in certain time interval. Our research has revealed that the number of detected glacier-origin events over last two years has doubled. Annual events distribution correlates well with temperature and precipitation curves, illustrating characteristic yearlong behaviour of glacier seismic activity. To further support our observations, we have analysed 5-year long distribution of glacier-origin tremors detected in the vicinity of the Kronebreen glacier using KBS broadband station located in Ny-Ålesund (western Spitsbergen). We observe a steady increase in the number of detected events. detected each year, however not as significant as for Hornsund dataset.

  10. Data Quality Control of the French Permanent Broadband Network in the RESIF Framework

    NASA Astrophysics Data System (ADS)

    Grunberg, Marc; Lambotte, Sophie; Engels, Fabien; Dretzen, Remi; Hernandez, Alain

    2014-05-01

    In the framework of the RESIF (Réseau Sismologique et géodésique Français) project, a new information system is being setting up, allowing the improvement of the management and the distribution of high quality data from the different elements of RESIF and the associated networks. Within this information system, EOST (in Strasbourg) is in charge of collecting real-time permanent broadband seismic waveform, and performing Quality Control on these data. The real-time and validated data set are pushed to the French National Distribution Center (Isterre/Grenoble) in order to make them publicly available. Furthermore EOST hosts the BCSF-ReNaSS, in charge of the French metropolitan seismic bulletin. This allows to benefit from some high-end quality control based on the national and world-wide seismicity. Here we present first the real-time seismic data flow from the stations of the French National Broad Band Network to EOST, and then, the data Quality Control procedures that were recently installed, including some new developments. The data Quality Control consists in applying a variety of subprocesses to check the consistency of the whole system and process from the stations to the data center. This allows us to verify that instruments and data transmission are operating correctly. Moreover analysis of the ambient noise helps to characterize intrinsic seismic quality of the stations and to identify other kind of disturbances. The deployed Quality Control consist in a pipeline that starts with low-level procedures : check the real-time miniseed data file (file naming convention, data integrity), check for inconsistencies between waveform and meta-data (channel name, sample rate, etc.), compute waveform statistics (data availability, gap/overlap, mean, rms, time quality, spike). It is followed by some high-level procedures such as : power spectral density computation (PSD), STA/LTA computation to be correlated to the seismicity, phases picking and stations magnitudes

  11. Crustal Structure of the Pakistan Himalayas from Ambient Noise and Seismic Rayleigh Wave Inversion

    NASA Astrophysics Data System (ADS)

    Li, A.

    2007-05-01

    The western Himalayan syntaxi is a unique feature resulted from the India-Asia collision and its formation remains poorly understood. To image crustal structure in the western syntaxi, we analyze Rayleigh waves from ambient seismic noise and earthquake data recorded during the Pakistan Broadband Seismic Experiment. The Pakistan experiment included 9 broadband stations with an aperture of ~200 km and operated from September to December in 1992. We compute cross-correlations of ambient noise data on an hourly base and stack all the cross-correlations for 70 days to produce the estimated Green functions. Power spectrum analysis shows that the dominant energy is from 0.15 to 0.25 Hz and from 0.05 to 0.07 Hz, consistent with the well-know background seismic noise. A phase with large amplitude appears at near zero time on almost all stacked cross- correlations and its origin is not clear to us at this moment. Rayleigh waves can be clearly observed for station pairs at the distance of 80 km and larger but are contaminated by the near zero time phase at shorter station spacing. Rayleigh wave phase velocities at periods of 4 to 15 s will be produced from the ambient noise data. Using regional and teleseismic earthquakes, we expect to obtain Rayleigh wave dispersions at periods from 15 to 50 s. The phase velocities from both datasets will be inverted for crustal thickness and shear-wave structure beneath the Pakistan Himalayas.

  12. Data Quality Analysis for the Bighorn Arch Seismic Array Experiment

    NASA Astrophysics Data System (ADS)

    Mancinelli, N. J.; Yang, Z.; Yeck, W. L.; Sheehan, A. F.

    2010-12-01

    We analyze background noise to assess the difference in station noise levels of different types of seismic sensors and the effects of deployed site locations, and to identify local noise sources, using the data from the Bighorn Arch Seismic Experiment (BASE). Project BASE is an EarthScope Flexible Array (FA) project and includes the deployment of 38 broadband seismometers (Guralp CMG3T), 173 short-period seismometers (L22 and CMG40T-1s), and 1850 high-frequency geophones with Reftek RT125 “Texans” in northern Wyoming, providing continuous dataset of various seismic sensor types and site locations in different geologic setups (basins and mountains). We carry out our analysis through a recently developed approach of using probability density function (PDF) to display the distribution of seismic power spectral density (PSD) [McNamara and Buland, 2004]. This new approach bypasses the tedious pre-screening for transient signals (earthquakes, mass recentering, calibration pulses, etc.) which is required by the traditional PSD analysis. Using the program PQLX, we were able to correlate specific noise sources—mine blasts, teleseisms, passing cars, etc—with features seen on PDF plots. We analyzed eight months of continuous BASE project broadband and short period data for this study. The power spectral density plots suggest that, of the 3 different instrument types used in the BASE project, the broadband CMG3T stations have the lowest background noise in the period range of 0.1-1 s while the short-period L22 stations have the highest background noise. As expected, stations located in the Bighorn Mountain Range are closer to the Low Noise Model [Peterson, 1993] than those located in the adjacent Bighorn Basin and Powder River Basin, particularly in the 0.1-1 s period range. This is mainly attributed to proximity to bedrock, though increased distance from cultural noise also contributes. At longer periods (1-100 s), the noise level of broadband instruments is lower

  13. Seismic Monitoring Developments In The North-eastern Italy

    NASA Astrophysics Data System (ADS)

    Michelini, A.; Crs Team

    NE Italy is an area affected by moderate seismicity with large events (ML>5.0) occur- ring with return period shorter than 50 years. Recently, two main events occurred in Friuli (May6, 1976, ML=6.4) and western Slovenia (April 12, 1998, ML=5,6). There- fore, the seismological monitoring of the area is of extreme importance from the sci- entific and the social point of view. At present, the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS) is monitoring the area with a short period seismic network including 17 stations covering the Friuli-Venezia Giulia and the north-east of the Veneto region. Furthermore, in cooperation with the University of Trieste, it operates two broad-band stations sited in Trieste and Villanova Grotte (central Friuli). OGS has now planned to extend its sensing capabilities by implementing a new inte- grated network including both short period and broad-band seismic stations as well as GPS stations for measures of deformation. The network will include new and existing instrumentation and will cover the area from the Garda lake to the slovenian border. Three main guidelines have inspired the design of such network: - on-line acquisition: data acquisition should occur in nearly real-time at the cen- tral stations in Udine. To this purpose, various transmission technologies will be considered (e.g. radio, telephone lines, GSM and satellite). - data integration: all data should be merged in the same database and made avail- able to the users through a uniform interface, independently from their type and modality of acquisition. - open access: data should be made available in near real-time to the entire sci- entific community, accessing the central data base and, when possible, directly the remote stations. The implementation of such goals will guarantee the full integration with the other networks covering the area, in particular the Slovenia and Austria networks. To this purpose, an experimental transfrontier broad-band network

  14. Utah's Regional/Urban ANSS Seismic Network---Strategies and Tools for Quality Performance

    NASA Astrophysics Data System (ADS)

    Burlacu, R.; Arabasz, W. J.; Pankow, K. L.; Pechmann, J. C.; Drobeck, D. L.; Moeinvaziri, A.; Roberson, P. M.; Rusho, J. A.

    2007-05-01

    The University of Utah's regional/urban seismic network (224 stations recorded: 39 broadband, 87 strong-motion, 98 short-period) has become a model for locally implementing the Advanced National Seismic System (ANSS) because of successes in integrating weak- and strong-motion recording and in developing an effective real-time earthquake information system. Early achievements included implementing ShakeMap, ShakeCast, point-to- multipoint digital telemetry, and an Earthworm Oracle database, as well as in-situ calibration of all broadband and strong-motion stations and submission of all data and metadata into the IRIS DMC. Regarding quality performance, our experience as a medium-size regional network affirms the fundamental importance of basics such as the following: for data acquisition, deliberate attention to high-quality field installations, signal quality, and computer operations; for operational efficiency, a consistent focus on professional project management and human resources; and for customer service, healthy partnerships---including constant interactions with emergency managers, engineers, public policy-makers, and other stakeholders as part of an effective state earthquake program. (Operational cost efficiencies almost invariably involve trade-offs between personnel costs and the quality of hardware and software.) Software tools that we currently rely on for quality performance include those developed by UUSS (e.g., SAC and shell scripts for estimating local magnitudes) and software developed by other organizations such as: USGS (Earthworm), University of Washington (interactive analysis software), ISTI (SeisNetWatch), and IRIS (PDCC, BUD tools). Although there are many pieces, there is little integration. One of the main challenges we face is the availability of a complete and coherent set of tools for automatic and post-processing to assist in achieving the goals/requirements set forth by ANSS. Taking our own network---and ANSS---to the next level

  15. Seismic signature of intracrustal magmatic intrusions in the Eastern Betics (Internal Zone), SE Iberia

    NASA Astrophysics Data System (ADS)

    Julià, J.; Mancilla, F.; Morales, J.

    2005-08-01

    Receiver functions at three broad-band stations located in the most easterly Inner Betics have been analyzed to investigate the structure of its underlying crust and uppermost mantle. These stations are located within a geologically distinctive block bounded by the Palomares/Alhama de Murcia faults, which is characterized by high heat-flow values, widespread strike-slip faulting and Neogene volcanism. Our analysis shows that a low velocity zone pervades the uppermost mantle beneath the stations, and that the overlying crust has a high Vp/Vs ratio and a prominent intracrustal low velocity zone (i) between the Palomares and Alhama de Murcia faults and (ii) east of Murcia, perhaps thermally perturbing the upper crust north and east of Cartagena. Independent studies show that the seismic velocities of the intervening mantle lid are normal beneath the stations, and we suggest that our observations result from rapidly ascending magma diapirs ponding at intracrustal levels within the distinctive block.

  16. Locating Local Earthquakes Using Single 3-Component Broadband Seismological Data

    NASA Astrophysics Data System (ADS)

    Das, S. B.; Mitra, S.

    2015-12-01

    We devised a technique to locate local earthquakes using single 3-component broadband seismograph and analyze the factors governing the accuracy of our result. The need for devising such a technique arises in regions of sparse seismic network. In state-of-the-art location algorithms, a minimum of three station recordings are required for obtaining well resolved locations. However, the problem arises when an event is recorded by less than three stations. This may be because of the following reasons: (a) down time of stations in a sparse network; (b) geographically isolated regions with limited logistic support to setup large network; (c) regions of insufficient economy for financing multi-station network and (d) poor signal-to-noise ratio for smaller events at most stations, except the one in its closest vicinity. Our technique provides a workable solution to the above problematic scenarios. However, our methodology is strongly dependent on the velocity model of the region. Our method uses a three step processing: (a) ascertain the back-azimuth of the event from the P-wave particle motion recorded on the horizontal components; (b) estimate the hypocentral distance using the S-P time; and (c) ascertain the emergent angle from the vertical and radial components. Once this is obtained, one can ray-trace through the 1-D velocity model to estimate the hypocentral location. We test our method on synthetic data, which produces results with 99% precision. With observed data, the accuracy of our results are very encouraging. The precision of our results depend on the signal-to-noise ratio (SNR) and choice of the right band-pass filter to isolate the P-wave signal. We used our method on minor aftershocks (3 < mb < 4) of the 2011 Sikkim earthquake using data from the Sikkim Himalayan network. Location of these events highlight the transverse strike-slip structure within the Indian plate, which was observed from source mechanism study of the mainshock and larger aftershocks.

  17. Development and experiment of a broadband seismograph for deep exploration

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Lin, J.; Yang, H.; Zheng, F.; Zhang, L.; Chen, Z.

    2012-12-01

    Seismic surveying is the most important type of deep exploration and oil-gas exploration. In order to obtain the high-quality deeper strata information in the deep exploration, large amount of drugs, large group interval and the low-frequency detector must be used, the length of the measuring line is usually tens of kilometers or even hundreds of kilometers. Conventional seismic exploration instrument generally do not have site storage function or limited storage capacity, due to the shackles of the transmission cable, the system bulky and difficult to handle, inefficient construction, high labor costs, collection capabilities and accuracy are the drawbacks of restrictions. This article describes a deep exploration of high-performance broadband seismograph. To ensure the quality of data acquisition, the 24-bit ADCs applied and the low noise analog front end circuit designed carefully, which enable the instrument noise level less than 1.5uV and the dynamic range over 120dB. Integrate dual-frequency GPS OEM board with the acquisition station. As a result, the acquisition station itself can make a static self-positioning and the horizontal accuracy can reach to centimeter-level. Furthermore, it can provide high accuracy position data to subsequent seismic data processing. Combine the precise timing system of GPS with digital clock that has high precision oven-controlled crystal oscillator (OCXO). It enables the accuracy of clock synchronization to reach 0.01ms and the stability of OCXO frequency reach 3e-8, which could solve the problems of synchronous triggering of the data acquisition unit of multiple recording units in the instrument and real-time calibration of the inaccuracy of system clock. The instrument uses a high-capacity (large than 16GB/station), high reliability of the seismic data storage solutions, which enables the instrument to record continuously for more than 138 hours at the sampling rate of 2000sps. Using low-power design techniques for power

  18. A Contribution to the Understanding of the Regional Seismic Structure in the Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Di Luccio, F.; Thio, H.; Pino, N.

    2001-12-01

    Regional earthquakes recorded by two digital broadband stations (BGIO and KEG) located in the Eastern Mediterranean have been analyzed in order to study the seismic structure in this region. The area consists of different tectonic provinces, which complicate the modeling of the seismic wave propagation. We have modeled the Pnl arrivals using the FK-integration technique (Saikia, 1994) along different paths at the two stations, at several distances, ranging from 400 to 1500 km. Comparing the synthetics obtained by using several models compiled by other authors, we have constructed a velocity model, considering the informations deriving from group velocity distribution, in order to determine the finer structure in the analyzed paths. The model has been perturbed by trial and error until a compressional velocity profile has been found producing the shape of the observed waveforms. The crustal thickness, upper mantle P-wave velocity and 410-km discontinuity determine the shape of the observed waveform portions.

  19. Seismic structure of the lithosphere beneath the ocean islands near the mid-oceanic ridges

    NASA Astrophysics Data System (ADS)

    Haldar, C.; Kumar, P.; Kumar, M. Ravi

    2013-10-01

    Deciphering the seismic character of the young lithosphere near the mid-oceanic ridges (MOR) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs, using the P-to-s conversions isolated from good quality data recorded at 5 broadband seismological stations situated on the ocean Islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform modeling of the P receiver function stacks reveal that the crustal thickness varies between 6 and 8 km with the corresponding depths to the lithosphere asthenosphere boundary (LAB) varying between 43 and 68 km. However, the depth to the LAB at Macquire Island is intriguing in view of the observation of a thick (~ 87 km) lithosphere beneath a relatively young crust. At three other stations i.e., Ascension Island, Sao Jorge and Easter Island, we find evidence for an additional deeper low velocity layer probably related to the presence of a hotspot.

  20. Seismic monitoring at Cascade Volcanic Centers, 2004?status and recommendations

    USGS Publications Warehouse

    Moran, Seth C.

    2004-01-01

    The purpose of this report is to assess the current (May, 2004) status of seismic monitoring networks at the 13 major Cascade volcanic centers. Included in this assessment are descriptions of each network, analyses of the ability of each network to detect and to locate seismic activity, identification of specific weaknesses in each network, and a prioritized list of those networks that are most in need of additional seismic stations. At the outset it should be recognized that no Cascade volcanic center currently has an adequate seismic network relative to modern-day networks at Usu Volcano (Japan) or Etna and Stromboli volcanoes (Italy). For a system the size of Three Sisters, for example, a modern-day, cutting-edge seismic network would ideally consist of a minimum of 10 to 12 short-period three-component seismometers (for determining particle motions, reliable S-wave picks, moment tensor inversions, fault-plane solutions, and other important seismic parameters) and 7 to 10 broadband sensors (which, amongst other considerations, enable detection and location of very long period (VLP) and other low-frequency events, moment tensor inversions, and, because of their wide dynamic range, on-scale recording of large-amplitude events). Such a dense, multi component seismic network would give the ability to, for example, detect in near-real-time earthquake migrations over a distance of ~0.5km or less, locate tremor sources, determine the nature of a seismic source (that is, pure shear, implosive, explosive), provide on-scale recordings of very small and very large-amplitude seismic signals, and detect localized changes in seismic stress tensor orientations caused by movement of magma bodies. However, given that programmatic resources are currently limited, installation of such networks at this time is unrealistic. Instead, this report focuses on identifying what additional stations are needed to guarantee that anomalous seismicity associated with volcanic unrest will be

  1. Stable and unstable phases of elevated seismic activity at the persistently restless Telica Volcano, Nicaragua

    NASA Astrophysics Data System (ADS)

    Rodgers, Mel; Roman, Diana C.; Geirsson, Halldor; LaFemina, Peter; McNutt, Stephen R.; Muñoz, Angelica; Tenorio, Virginia

    2015-01-01

    Telica Volcano, Nicaragua, is a persistently restless volcano with daily seismicity rates that can vary by orders of magnitude without apparent connection to eruptive activity. Low-frequency (LF) events are dominant and peaks in seismicity rate show little correlation with eruptive episodes, presenting a challenge for seismic monitoring and eruption forecasting. A short period seismic station (TELN) has been operated on Telica's summit since 1993, and in 2010 the installation of a six-station broadband seismic and eleven-station continuous GPS network (the TESAND network) was completed to document in detail the seismic characteristics of a persistently restless volcano. Between our study period of November 2009 and May 2013, over 400,000 events were detected at the TESAND summit station (TBTN), with daily event rates ranging from 5 to 1400. We present spectral analyses and classifications of ~ 200,000 events recorded by the TESAND network between April 2010 and March 2013, and earthquake locations for a sub-set of events between July 2010 and February 2012. In 2011 Telica erupted in a series of phreatic vulcanian explosions. Six months before the 2011 eruption, we observe a sudden decrease in LF events concurrent with a swarm of high-frequency (HF) events, followed by a decline in overall event rates, which reached a minimum at the eruption onset. We observe repeated periods of high and low seismicity rates and suggest these changes in seismicity represent repeated transitions between open-system and closed-system degassing. We suggest that these short- and long-term transitions between open to closed-system degassing form part of a long-term pattern of stable vs. unstable phases at Telica. Stable phases are characterised by steady high-rate seismicity and represent stable open-system degassing, whereas unstable phases are characterised by highly variable seismicity rates and represent repeated transitions from open to closed-system degassing, where the system is

  2. Yellowstone Attenuation Tomography from Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Doungkaew, N.; Seats, K.; Lawrence, J. F.

    2013-12-01

    The goal of this study is to create a tomographic attenuation image for the Yellowstone region by analyzing ambient seismic noise. An attenuation image generated from ambient noise should provide more information about the structure and properties beneath Yellowstone, especially the caldera, which is known to be active. I applied the method of Lawrence & Prieto [2011] to examine lateral variations in the attenuation structure of Yellowstone. Ambient noise data were collected from broadband seismic stations located around Yellowstone National Park from 1999-2013. Noise correlation functions derived from cross correlations of the ambient noise at two stations were used to calculate a distance dependent decay (an attenuation coefficient) at each period and distance. An inversion was then performed to isolate and localize the spatial attenuation coefficients within the study area. I observe high amplitude decay of the ambient noise at the Yellowstone caldera, most likely due to elevated temperature and crustal melts caused by volcanism, geothermal heat flow, and hydrothermal activity such as geysers.

  3. Investigation of anthropogenic and natural noise at Bucovina and Plostina seismic arrays, Romania

    NASA Astrophysics Data System (ADS)

    Grecu, Bogdan; Borleanu, Felix; Neagoe, Cristian; Zaharia, Bogdan; Tataru, Dragos

    2016-04-01

    At present, two seismic arrays are installed on the Romanian territory and record continuously the ground motion and send the data in real time to the National Data Center, in Magurele, Romania. One array is located in the Northern part of the country, in Bucovina (BURAR array), while the second one (Plostina - PLOR array) is situated right above the Vrancea seismic nest, the region with the highest seismic activity in Romania. The BURAR array consists of ten stations with seismic sensors installed in boreholes at depths of 30 and 50 m, covering an area of 5x5 km2. Nine stations are equipped with GS21 short period vertical sensors and one station has a 3-component broadband sensor (KS54000). In 2008, three more 3-component broadband sensors (CMG-40T) were installed at surface; two of them collocated with existing sites and one in a different site. The PLOR array consists of 7 elements equipped with 3-component broadband sensors (CMG40T - 6 and STS2 - 1). The aperture of the array is 2.5 km, with a distance between inner elements of 250 m and 1100 m for the outer elements. We analyze the power spectral density of BURAR and PLOR arrays continuous records to characterize the temporal noise variations and investigate their influence on the detection capabilities for intermediate-depth earthquakes, occurred in Vrancea region, as well as for local crustal events produced in various places of the country. We also perform polarization and array specific analyses to identify the main sources of the high frequency noise and secondary microseisms. Diurnal variations caused by anthropogenic activities have been observed at all stations, but their significance depends strongly on the distance to the sources of the noise. For BURAR array, the maximum difference between nighttime and daytime noise levels is 25 dB, while for PLOR array we observe differences up to 42 dB. In the microseismic band, the noise variations are correlated well with the seasons and have their maximum

  4. 100 years of seismic research on the Moho

    NASA Astrophysics Data System (ADS)

    Prodehl, Claus; Kennett, Brian; Artemieva, Irina M.; Thybo, Hans

    2013-12-01

    The detection of a seismic boundary, the “Moho”, between the outermost shell of the Earth, the Earth's crust, and the Earth's mantle by A. Mohorovičić was the consequence of increased insight into the propagation of seismic waves caused by earthquakes. This short history of seismic research on the Moho is primarily based on the comprehensive overview of the worldwide history of seismological studies of the Earth's crust using controlled sources from 1850 to 2005, by Prodehl and Mooney (2012). Though the art of applying explosions, so-called “artificial events”, as energy sources for studies of the uppermost crustal layers began in the early 1900s, its effective use for studying the entire crust only began at the end of World War II. From 1945 onwards, controlled-source seismology has been the major approach to study details of the crust and underlying crust-mantle boundary, the Moho. The subsequent description of history of controlled-source crustal seismology and its seminal results is subdivided into separate chapters for each decade, highlighting the major advances achieved during that decade in terms of data acquisition, processing technology, and interpretation methods. Since the late 1980s, passive seismology using distant earthquakes has played an increasingly important role in studies of crustal structure. The receiver function technique exploiting conversions between P and SV waves at discontinuities in seismic wavespeed below a seismic station has been extensively applied to the increasing numbers of permanent and portable broad-band seismic stations across the globe. Receiver function studies supplement controlled source work with improved geographic coverage and now make a significant contribution to knowledge of the nature of the crust and the depth to Moho.

  5. Broadband waveform inversion of moderate earthquakes in the Messina Straits, southern Italy

    NASA Astrophysics Data System (ADS)

    D'Amico, Sebastiano; Orecchio, Barbara; Presti, Debora; Zhu, Lupei; Herrmann, Robert B.; Neri, Giancarlo

    2010-04-01

    We report the first application of the Cut and Paste (CAP) method to compute earthquake focal mechanisms in the Messina Straits area by waveform inversion of Pnl and surface wave segments. This application of CAP has furnished new knowledge about low-magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics. This is possible because the CAP inversion technique can be applied to small earthquakes, for which traditional moment tensor inversion methods are not appropriate and P-onset focal mechanisms in the study area fail because of a lack of sufficient observations. We estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3-4 occurring in the 2004-2008 time period, and recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co-existence of normal faulting and strike-slip has been detected in the southern part. In the whole area of investigation the T-axes of focal mechanisms display a preferential northwest-southeast direction of extension. Combined with the findings of previous investigations, this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat (southern Calabria) and the compressional one associated with continental collision (western-central Sicily). The observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of Messina Straits where a magnitude 7.2 earthquake caused more than 60,000 casualties on 28 December 1908.

  6. The Berkeley Digital Seismic Network

    NASA Astrophysics Data System (ADS)

    Romanowicz, B.; Dreger, D.; Neuhauser, D.; Karavas, W.; Hellweg, M.; Uhrhammer, R.; Lombard, P.; Friday, J.; Lellinger, R.; Gardner, J.; McKenzie, M. R.; Bresloff, C.

    2007-05-01

    Since it began monitoring earthquakes in northern California 120 years ago, the Berkeley Seismological Laboratory (BSL) has been striving to produce the highest quality and most complete seismic data possible in the most modern way. This goal has influenced choices in instrumentation, installation and telemetry, as well as the investment in expertise and manpower. Since the transition to broadband (BB) instrumentation in the mid- 1980s and to a fully digitally telemetered network in the early 1990s, we have continued these efforts. Each of our 25 BB installations includes three component BB seismometers (STS-1s or STS-2) and digital accelerometers to capture the full range of ground motion from distant teleseisms to large, nearby earthquakes (almost 250 dB). The ground motion is recorded on-site by 24 bit dataloggers. Additional environmental parameters, such as temperature and pressure, are also monitored continuously. Many stations record also C-GPS data that is transmitted continuously to the BSL via shared real-time telemetry. The BDSN's first stations were installed in abandoned mines. In the last 15 years, we developed installations using buried shipping containers to reduce environmental noise and provide security and easy access to the equipment. Data are transmitted in real-time at several sampling rates to one or more processing centers, using frame relay, radio, microwave, and/or satellite. Each site has 7-30 days of onsite data storage to guard against data loss during telemetry outages. Each station is supplied with backup batteries to provide power for 3 days. The BDSN real-time data acquisition, earthquake analysis and archiving computers are housed in a building built to "emergency grade" seismic standards, with air conditioning and power backed up by a UPS and a large generator. Data latency and power are monitored by automated processes that alert staff via pager and email. Data completeness and timing quality are automatically assessed on a daily

  7. Broadband Lg Attenuation Modeling in the Middle East

    SciTech Connect

    Pasyanos, M E; Matzel, E M; Walter, W R; Rodgers, A J

    2008-08-21

    We present a broadband tomographic model of Lg attenuation in the Middle East derived from source- and site-corrected amplitudes. Absolute amplitude measurements are made on hand-selected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region. A conjugate gradient method is used to tomographically invert the amplitude dataset of over 8000 paths over a 45{sup o} x 40{sup o} region of the Middle East. We solve for Q variation, as well as site and source terms, for a wide range of frequencies ranging from 0.5-10 Hz. We have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment. This facilitates the use of the model to predict the expected amplitudes of new events, an important consideration for earthquake hazard or explosion monitoring applications. The attenuation results have a strong correlation to tectonics. Shields have low attenuation, while tectonic regions have high attenuation, with the highest attenuation at 1 Hz is found in eastern Turkey. The results also compare favorably to other studies in the region made using Lg propagation efficiency, Lg/Pg amplitude ratios and two-station methods. We tomographically invert the amplitude measurements for each frequency independently. In doing so, it appears the frequency-dependence of attenuation is not compatible with the power law representation of Q(f), an assumption that is often made.

  8. Broadband regional waveform modeling to investigate crustal structure and tectonics of the central Andes

    NASA Astrophysics Data System (ADS)

    Swenson, Jennifer Lyn

    We use broadband regional waveform modeling of earthquakes in the central Andes to determine seismic properties of the Altiplano crust. Properties of the shear-coupled P-wavetrain (SPL ) from intermediate-depth events provide particularly important information about the structure of the crust. We utilize broadband seismic data recorded at the BANJO and SEDA stations, and synthetic seismograms computed with a reflectivity technique to study the sensitivity of SPL to crustal and upper mantle parameters at regional distances. We find that the long-period SPL-wavetrain is most sensitive to crustal and mantle Poisson's ratios, average crustal velocity, and crustal thickness. A comprehensive grid search method developed to investigate these four parameters suggests that although trade-offs exist between model parameters, models of the Altiplano which provide the best fit between the data and synthetic seismograms are characterized by low Poisson's ratios, low average crustal velocity and thick crust. We apply our grid search technique and sensitivity analysis results to model the full waveforms from 6 intermediate-depth and 2 shallow-focus earthquakes recorded at regional distances by BANJO and SEDA stations. Results suggest that the Altiplano crust is much thicker (55--65 km) and slower (5.75--6.25 km/s) than global average values. Low crustal and mantle Poisson's ratios together with the lack of evidence for a high-velocity lower crust suggests a bulk felsic crustal composition, resulting in an overall weak crust. Our results favor a model of crustal thickening involving large-scale tectonic shortening of a predominantly felsic crust. To better understand the mechanics of earthquake rupture along the South American subduction zone, we have analyzed broadband teleseismic P-waves and utilize single- and multi-station inversion techniques to constrain source characteristics for the 12 November 1996 Peru subduction zone earthquake. Aftershock locations, intensity reports

  9. Monitoring Velocity Changes Caused By Underground Coal Mining Using Seismic Noise

    NASA Astrophysics Data System (ADS)

    Czarny, Rafał; Marcak, Henryk; Nakata, Nori; Pilecki, Zenon; Isakow, Zbigniew

    2016-06-01

    We use passive seismic interferometry to monitor temporal variations of seismic wave velocities at the area of underground coal mining named Jas- Mos in Poland. Ambient noise data were recorded continuously for 42 days by two three-component broadband seismometers deployed at the ground surface. The sensors are about 2.8 km apart, and we measure the temporal velocity changes between them using cross-correlation techniques. Using causal and acausal parts of nine-component cross-correlation functions (CCFs) with a stretching technique, we obtain seismic velocity changes in the frequency band between 0.6 and 1.2 Hz. The nine-component CCFs are useful to stabilize estimation of velocity changes. We discover correlation between average velocity changes and seismic events induced by mining. Especially after an event occurred between the stations, the velocity decreased about 0.4 %. Based on this study, we conclude that we can monitor the changes of seismic velocities, which are related to stiffness, effective stress, and other mechanical properties at subsurface, caused by mining activities even with a few stations.

  10. Subsurface fluid distribution and possible seismic precursory signal at the Salse di Nirano mud volcanic field, Italy

    NASA Astrophysics Data System (ADS)

    Lupi, Matteo; Ricci, Barbara Suski; Kenkel, Johannes; Ricci, Tullio; Fuchs, Florian; Miller, Stephen A.; Kemna, Andreas

    2016-02-01

    Mud volcanoes are geological systems often characterized by elevated fluid pressures at depth deviating from hydrostatic conditions. This near-critical state makes mud volcanoes particularly sensitive to external forcing induced by natural or man-made perturbations. We used the Nirano mud volcanic field as a natural laboratory to test pre- and post-seismic effects generated by distant earthquakes. We first characterized the subsurface structure of the Nirano mud volcanic field with a geoelectrical study. Next, we deployed a broad-band seismic station in the area to understand the typical seismic signal generated by the mud volcano. Seismic records show a background noise below 2 s, sometimes interrupted by pulses of drumbeat-like high-frequency signals lasting from several minutes to hours. To date this is the first observation of drumbeat signal observed in mud volcanoes. In 2013 June we recorded a M4.7 earthquake, that occurred approximately 60 km far from our seismic station. According to empirical estimations the Nirano mud volcanic field should not have been affected by the M4.7 earthquake. Yet, before the seismic event we recorded an increasing amplitude of the signal in the 10-20 Hz frequency band. The signal emerged approximately two hours before the earthquake and lasted for about three hours. Our statistical analysis suggests the presence of a possible precursory signal about 10 min before the earthquake.

  11. Imaging architecture of the Jakarta Basin, Indonesia with transdimensional inversion of seismic noise

    NASA Astrophysics Data System (ADS)

    Saygin, E.; Cummins, P. R.; Cipta, A.; Hawkins, R.; Pandhu, R.; Murjaya, J.; Masturyono, Irsyam, M.; Widiyantoro, S.; Kennett, B. L. N.

    2016-02-01

    In order to characterize the subsurface structure of the Jakarta Basin, Indonesia, a dense portable seismic broad-band network was operated by The Australian National University (ANU) and the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) between October 2013 and February 2014. Overall 96 locations were sampled through successive deployments of 52 seismic broad-band sensors at different parts of the city. Oceanic and anthropogenic noises were recorded as well as regional and teleseismic earthquakes. We apply regularized deconvolution to the recorded ambient noise of the vertical components of available station pairs, and over 3000 Green's functions were retrieved in total. Waveforms from interstation deconvolutions show clear arrivals of Rayleigh fundamental and higher order modes. The traveltimes that were extracted from group velocity filtering of fundamental mode Rayleigh wave arrivals, are used in a 2-stage Transdimensional Bayesian method to map shear wave structure of subsurface. The images of S wave speed show very low velocities and a thick basin covering most of the city with depths up to 1.5 km. These low seismic velocities and the thick basin beneath the city potentially cause seismic amplification during a subduction megathrust or other large earthquake close to the city of Jakarta.

  12. A Large-N Mixed Sensor Active + Passive Seismic Array near Sweetwater, TX

    NASA Astrophysics Data System (ADS)

    Barklage, M.; Hollis, D.; Gridley, J. M.; Woodward, R.; Spriggs, N.

    2014-12-01

    A collaborative high-density seismic survey using broadband and short period seismic sensors was conducted March 7 - April 30, 2014 near Sweetwater, TX. The objective of the survey was to use a combination of controlled source shot slices and passive seismic recordings recorded by multiple types of sensors with different bandwidths and sensitivities to image the subsurface. The broadband component of the survey consisted of 25 continuously recording seismic stations comprised of 20 Trillium Compact Posthole sensors from Nanometrics and 5 Polar Trillium 120PHQs from the IRIS/PASSCAL Instrument Center (PIC). The broadband stations also utilized 25 Centaur digitizers from Nanometrics as well as 25 polar quick deploy enclosures from the PIC. The broadband array was designed to maximize horizontal traveling seismic energy for surface wave analysis over the primary target area with sufficient offset for imaging objectives at depth. The short period component of the survey consisted of 2639 receiver locations using Zland nodes from NodalSeismic. The nodes are further divided into 3 sub-arrays: 1) outlier array 2) active source array 3) backbone array. The outlier array consisted of 25 continuously recording nodes distributed around the edge of the survey at a distance of ~5 km from the survey boundary, and provided valuable constraints to passive data analysis techniques at the edge of the survey boundary. The active source patch consisted of densely spaced nodes that were designed to record signals from a Vibroseis source truck for active source reflection processing and imaging. The backbone array consisted of 292 nodes that covered the entirety of the survey area to maximize the value of the passive data analysis. By utilizing continuous recording and smartly designed arrays for measuring local and regional earthquakes we can incorporate velocity information derived from passive data analysis into the active source processing workflow to produce a superior subsurface

  13. Seismic detections of the 15 February 2013 Chelyabinsk meteor from the dense ChinArray

    NASA Astrophysics Data System (ADS)

    Li, Lu; Wang, Baoshan; Peng, Zhigang; Wang, Weitao

    2016-07-01

    ChinArray is a dense portable broadband seismic network to cover the entire continental China, and the Phase I is deployed along the north-south seismic belt in southwest China. In this study, we analyze seismic data recorded on the ChinArray following the February 15, 2013 Chelyabinsk (Russia) meteor. This was the largest known object entering the Earth's atmosphere since the 1908 Tunguska meteor. The seismic energy radiated from this event was recorded by seismic stations worldwide including the dense ChinArray that are more than 4000 km away. The weak signal from the meteor event was contaminated by a magnitude 5.8 Tonga earthquake occurred ~20 min earlier. To test the feasibility of detecting the weak seismic signals from the meteor event, we compute vespagram and perform F-K analysis to the surface-wave data. We identify a seismic phase with back azimuth (BAZ) of 329.7° and slowness of 34.73 s/deg, corresponding to the surface wave from the Russian meteor event (BAZ ~325.97°). The surface magnitude (M S) of the meteor event is 3.94 ± 0.18. We also perform similar analysis on the data from the broadband array F-net in Japan, and find the BAZ of the surface waves to be 316.61°. With the different BAZs of ChinArray and F-net, we locate the Russian meteor event at 58.80°N, 58.72°E. The relatively large mislocation (~438 km as compared with 55.15°N, 61.41°E by others) may be a result of the bending propagation path of surface waves, which deviates from the great circle path. Our results suggest that the dense ChinArray and its subarrays could be used to detect weak signals at teleseismic distances.

  14. Seismic detections of the 15 February 2013 Chelyabinsk meteor from the dense ChinArray

    NASA Astrophysics Data System (ADS)

    Li, Lu; Wang, Baoshan; Peng, Zhigang; Wang, Weitao

    2016-08-01

    ChinArray is a dense portable broadband seismic network to cover the entire continental China, and the Phase I is deployed along the north-south seismic belt in southwest China. In this study, we analyze seismic data recorded on the ChinArray following the February 15, 2013 Chelyabinsk (Russia) meteor. This was the largest known object entering the Earth's atmosphere since the 1908 Tunguska meteor. The seismic energy radiated from this event was recorded by seismic stations worldwide including the dense ChinArray that are more than 4000 km away. The weak signal from the meteor event was contaminated by a magnitude 5.8 Tonga earthquake occurred ~20 min earlier. To test the feasibility of detecting the weak seismic signals from the meteor event, we compute vespagram and perform F-K analysis to the surface-wave data. We identify a seismic phase with back azimuth (BAZ) of 329.7° and slowness of 34.73 s/deg, corresponding to the surface wave from the Russian meteor event (BAZ ~325.97°). The surface magnitude ( M S) of the meteor event is 3.94 ± 0.18. We also perform similar analysis on the data from the broadband array F-net in Japan, and find the BAZ of the surface waves to be 316.61°. With the different BAZs of ChinArray and F-net, we locate the Russian meteor event at 58.80°N, 58.72°E. The relatively large mislocation (~438 km as compared with 55.15°N, 61.41°E by others) may be a result of the bending propagation path of surface waves, which deviates from the great circle path. Our results suggest that the dense ChinArray and its subarrays could be used to detect weak signals at teleseismic distances.

  15. The seismic structure beneath the Yellowstone Volcano Field from ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Seats, Kevin J.; Lawrence, Jesse F.

    2014-12-01

    We evaluate Rayleigh wave group velocity dispersion (5-40 s) around the Yellowstone Volcano Field with ambient noise tomography, measured from vertical component noise correlation functions. We include broadband data from 239 seismic stations (1999-2012), including USArray's Transportable Array and the Noise Observatory for Imaging the Subsurface beneath Yellowstone (NOISY). Short-period (<13 s) group velocity anomalies are imaged for the Bighorn Basin (~25% slow) and Range (~20% fast), and the Yellowstone Plateau (~10% fast). Beneath the Yellowstone caldera, Rayleigh wave group velocities are ~25% slower than the regional average with slow anomalies (<-15%) observed from 5 to 24 s. These values are consistent with a magmatic body being heated from below by an underlying plume.

  16. Seismic Tomography of the South Carpathian System

    NASA Astrophysics Data System (ADS)

    Stuart, G. W.; Ren, Y.; Dando, B. D.; Houseman, G.; Ionescu, C.; Hegedus, E.; Radovanovic, S.; South Carpathian Project Working Group

    2010-12-01

    The South Carpathian Mountain Range is an enigmatic system, which includes one of the most seismically active regions in Europe today. That region, Vrancea in the SE Carpathians, is well studied and its deep structure may be geologically unique, but the mantle structures beneath the western part of the South Carpathian Range are not well resolved by previous tomographic studies. The South Carpathian Project (SCP) is a major temporary deployment (2009-2011) of seismic broadband systems extending across the eastern Pannonian Basin and the South Carpathian Mountains. In this project we aim to map the upper mantle structure in central Europe with the objective of testing geodynamic models of the process that produced extension in the Pannonian, synchronous with convergence and uplift in the Carpathians. Here, we describe initial results of finite-frequency tomography using body waves to image the mantle of the region. We have selected teleseismic earthquakes with magnitude greater than 5.9, which occurred between 2005 and 2010. The data were recorded on 57 temporary stations deployed in the South Carpathian Project, 56 temporary stations deployed in the earlier Carpathian Basins Project (CBP), and 41 permanent broadband stations. The differential travel times are measured in high, intermediate and low frequencies (0.5-2.0 Hz, 0.1-0.5 Hz and 0.03-0.1 Hz for both P-wave, 0.1-0.5 Hz, 0.05-0.1 Hz and 0.02-0.05 Hz for S-wave), and are inverted to produce P and S-wave velocity maps at different depths in the mantle. An extensive zone of high seismic velocities is located in the Mantle Transition zone beneath the Pannonian Basin, and is related to down-welling associated with an earlier phase of continental convergence in the Pannonian region. These results will be used in conjunction with 3D geodynamical modelling to help understand the geological evolution of this region. SCP working group: G. Houseman, G. Stuart, Y. Ren, B. Dando, P. Lorinczi, School of Earth and

  17. Strategy for the deployment of a dense broadband temporary array in the Alps: lessons learnt from the CIFALPS experiment

    NASA Astrophysics Data System (ADS)

    Coralie, Aubert; Anne, Paul; Stefano, Solarino; Sandrine, Roussel; Simone, Salimbeni; Pierre, Zangelmi; Glenn, Cougoulat; Yinshuang, Ai; Weiwei, Xu; Yumei, He; Liang, Zhao

    2013-04-01

    The CIFALPS (China-Italy-France Alps seismic survey) experiment is a common project of IGGCAS (China), ISTerre (France) and INGV (Italy). It aims at getting new high-resolution passive seismic data on the crustal and upper mantle structure of the southwestern Alps. In this framework, we have installed a temporary broadband seismic array across the southwestern Alps from the Rhône valley (France) to the Po plain (Italy). The main sub-array of CIFALPS is a 350-km long roughly linear profile of 46 stations trending WSW-ENE from Bollène (France) to north of Alessandria (Italy). The average station spacing is 10 km in the outer parts of the belt, and it reduces to 5 km in the internal Alps. Nine additional temporary stations located ~40 km to the north and south of the main profile complement the permanent broadband networks to improve the 3-D constraints on the deep structures. Stations are equipped with Nanometrics Taurus data acquisition systems, and Trillium 120P/A, CMG3-ESP or CMG40T broadband sensors. The array was installed in the summer of 2012 and will be operated at least to April 2013. Because our schedule was tight, we had to achieve site selections in only 3-4 months in spite of strong constraints on site location related to short interstation spacing. Most sites are located in basements of buildings for security reasons and mains power supply. As most sensors are true broadband (90s or 120s), we put much effort on vault design to insure good thermal insulation and low noise at long periods. The vaults also had to be easily and rapidly built and they should be easily and totally removed at the end of the experiment. We used the PQLX software for quality control of our sites and vault design. The performances of our vaults are good for the vertical component with noise levels at 100s period in the range -185 dB (low noise model) to -165 dB. They are less good for horizontal components (noise level close to high noise model at periods > 20s) due to

  18. Migration of a coarse fluvial sediment pulse detected by hysteresis in bedload generated seismic waves

    NASA Astrophysics Data System (ADS)

    Roth, D. L.; Finnegan, N. J.; Brodsky, E. E.; Cook, K. L.; Stark, C. P.; Wang, H. W.

    2014-10-01

    Seismic signals near rivers are partially composed of the elastic waves generated by bedload particles impacting the river bed. In this study, we explore the relationship between this seismic signal and river bedload transport by analyzing high-frequency broadband seismic data from multiple stations along the Chijiawan River in northern Taiwan following the removal of a 13 m check dam. This dam removal provides a natural experiment in which rapid and predictable changes in the river's profile occur, which in turn enables independent constraints on spatial and temporal variation in bedload sediment transport. We compare floods of similar magnitudes with and without bedload transport, and find that the amplitude of seismic shaking produced at a given river stage changes over the course of a single storm when bedload transport is active. Hysteresis in the relationship between bedload transport and river stage is a well-documented phenomenon with multiple known causes. Consequently, previous studies have suggested that hysteresis observed in the seismic amplitude-stage response is the signature of bedload transport. Field evidence and stream profile evolution in this study corroborate that interpretation. We develop a metric (Ψ) for the normalized magnitude of seismic hysteresis during individual floods. This metric appears to scale qualitatively with total bedload transport at each seismic station, indicating a dominance of transport on the rising limbs of both storms. We speculate that hysteresis at this site arises from time-dependent evolution of the bed, for example due to grain packing, mobile armoring, or the temporal lag between stage and bedform growth. Ψ reveals along-stream variations in hysteresis for each storm, with a peak in hysteresis further downstream for the second event. The pattern is consistent with a migrating sediment pulse that is a predicted consequence of the dam removal. Our results indicate that hysteresis in the relationship between

  19. Ambient Seismic Noise Tomography of Southern Norway

    NASA Astrophysics Data System (ADS)

    Köhler, Andreas; Weidle, Christian; Maupin, Valerie

    2010-05-01

    The noise cross-correlation technique is especially useful in regions like southern Norway since local seismicity is rare and teleseismic records are not able to resolve the upper crust. Within the TopoScandiaDeep project, which aims to investigate the relation between surface topography and lithosphere-asthenosphere structure, we process seismic broadband data from the temporary MAGNUS network in Southern Norway. The receivers were recording 20 months of continuous data between September 2006 and June 2008. Additionally, permanent stations of the National Norwegian Seismic Network, NORSAR and GSN stations in the region are used. After usual preprocessing steps (filtering, prewhitening, temporal normalization), we compute 820 cross-correlation functions from 41 receivers for three month time windows. Evaluation of the azimuthal and temporal variation of signal to noise ratios and f-k analysis of NORSAR array data shows that the dominant propagation direction of seismic noise is south-west to north, corresponding well to the Norwegian coast line. During summer months, the signal to noise ratios decrease and the azimuthal distribution becomes smoother. Time-frequency analysis is applied to measure Rayleigh and Love wave group velocity dispersion curves between each station pair for each three-month correlation stack. The mean and variance of all dispersion curves is computed for each path. After rejection of low-quality data using a signal to noise ratio, minimum wavelength and velocity variance criterion, we obtain a large number of reliable velocity estimates (about 600) for periods between 2 and 15 seconds, which we invert for group velocity maps at respective periods. At all inverted periods, we find positive and negative velocity anomalies for Rayleigh and Love waves that correlate very well with local surface geology. While higher velocities (+5%) can be associated with the Caledonian nappes in the central part of southern Norway, the Oslo Graben is reflected

  20. Seismicity within the Irpinia Fault System As Monitored By Isnet (Irpinia Seismic Network) and Its Possible Relation with Fluid Storage

    NASA Astrophysics Data System (ADS)

    Festa, G.; Zollo, A.; Amoroso, O.; Ascione, A.; Colombelli, S.; Elia, L.; Emolo, A.; Martino, C.; Mazzoli, S.; Orefice, A.; Russo, G.

    2014-12-01

    ISNet (http://isnet.fisica.unina.it) is deployed in Southern Apennines along the active fault system responsible for the 1980, M 6.9 Irpinia earthquake. ISNet consists of 32 seismic stations equipped with both strong motion and velocimetric instruments (either broadband or short-period), with the aim of capture a broad set of seismic signals, from ambient noise to strong motion. Real time and near real time procedures run at ISNet with the goal of monitoring the seismicity, check possible space-time anomalies, detect seismic sequences and launch an earthquake early warning in the case of potential significant ground shaking in the area. To understand the role of fluids on the seismicity of the area, we investigated velocity and attenuation models. The former is built from accurate cross-correlation picking and S wave detection based onto polarization analysis. Joint inversion of both P and S arrival times is then based on a linearized multi-scale tomographic approach. Attenuation is instead obtained from inversion of displacement spectra, deconvolving for the source effect. High VP/VS and QS/QP >1 were found within a ~15 km wide rock volume where intense microseismicity is located. This indicates that concentration of seismicity is possibly controlled by high pore fluid pressure. This earthquake reservoir may come from a positive feedback between the seismic pumping that controls the fluid transmission through the fractured damage zone and the low permeability of cross fault barrier, increasing the fluid pore pressure within the fault bounded block. In this picture, sequences mostly occur at the base of this fluid rich layer. They show an anomalous pattern in the earthquake occurrence per magnitude classes; main events evolve with a complex source kinematics, as obtained from backprojection of apparent source time functions, indicating possible directivity effects. In this area sequences might be the key for understanding the transition between the deep

  1. Seismically Articulating Kilauea Volcano's Active Conduits, Rift Zones, and Faults through HVO's Second Fifty Years

    NASA Astrophysics Data System (ADS)

    Okubo, P.; Nakata, J.; Klein, F.; Koyanagi, R.; Thelen, W.

    2011-12-01

    While seismic monitoring of active Hawaiian volcanoes began 100 years ago, the build-up of the U. S. Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO) seismographic network to its current configuration began in 1955, when Jerry Eaton established remote stations that telemetered data via landline to recorders at HVO. With network expansion through the 1960's, earthquake location and cataloging capabilities have evolved to afford a computer processed seismic catalog now spanning fifty years. Location accuracy and catalog completeness to smaller magnitudes have increased. Research and insights developed using HVO's seismic record have exploited the ability to seismically monitor volcanic activity at depth, to identify active regions within the volcanoes on the basis of computed hypocentral locations, to infer regions of magma storage by recognizing different families of volcanic earthquakes, and to forecast volcanic activity in both short and longer term from seismicity patterns. HVO's seismicity catalog was central to calculations of probabilistic seismic hazards. The ability to develop and implement additional analytical and interpretive capabilities has kept pace with improvements in both field and laboratory hardware and software. While the basic capabilities continue as part of HVO's core monitoring, additional interpretive capabilities now include adding details of volcanic and earthquake source regions, and viewing seismic data in juxtaposition with other observatory data streams. As HVO looks to its next century of volcano studies, research and development continue to shape the future. Broadband seismic recording at HVO has enabled extensive study by Chouet, Dawson, and co-workers of the relationship of very-long-period seismic sources beneath Kilauea's summit caldera to magma supply and transport. Recent upgrades have improved the ability to use these data in seismic cataloging and research. Data processing upgrades have bolstered the ability to

  2. Detection of precursory slips on a fault by the quiescence and activation of seismicity relative to the ETAS model and by the anomalous trend of the geodetic time series of distances between GPS stations around the fault

    NASA Astrophysics Data System (ADS)

    Ogata, Y.

    2006-12-01

    This paper is concerned with the detection of precursory slip on a rupturing fault, supported by both seismic and geodetic records. Basically, the detection relies on the principle that, assuming precursory slip on the rupturing fault, the seismic activity around the fault should be enhanced or reduced in the zones where increment of the Coulomb failure stress (CFS) is positive or negative, respectively. However, any occurring event also affects the stress changes in neighboring regions, which can trigger further aftershock clusters. Whereas such stress transfers are too difficult to be computed precisely, due to the unknown complex fault system, the ordinary short-term occurrence rate of earthquakes in a region is easily predicted using the ETAS model of triggering seismicity; and any anomalous seismic activity, such as quiescence and activation, can be quantified by identifying a significant deviation from the predicted rate. Such anomalies are revealed to have occurred during several years leading up to the 2004 Chuetsu Earthquake of M6.8, central Honshu, and also the 2005 Western Fukuoka-Ken-Oki Earthquake of M7.0, Kyushu, Japan. Quiescence and activation in the regions coincided with negative and positive increments of the CFS, respectively, and were probably transferred from possible aseismic slips on the focal fault plane. Such slips are further supported by transient crustal movement around the source preceding the rupture. Time series records of the baseline distances between the permanent GPS stations deviated from the predicted trends, with the deviations consistent with the coseismic horizontal displacements of the stations due to these earthquakes. References Ogata, Y. (2006) Report of the Coordinating Committee for Earthquake Prediction, 76 (to appear, in Japanese).

  3. Seismic Characterization of Coal-Mining Seismicity in Utah for CTBT Monitoring

    SciTech Connect

    Arabasz, W J; Pechmann, J C

    2001-03-01

    Underground coal mining (down to {approx}0.75 km depth) in the contiguous Wasatch Plateau (WP) and Book Cliffs (BC) mining districts of east-central Utah induces abundant seismicity that is monitored by the University of Utah regional seismic network. This report presents the results of a systematic characterization of mining seismicity (magnitude {le} 4.2) in the WP-BC region from January 1978 to June 2000-together with an evaluation of three seismic events (magnitude {le} 4.3) associated with underground trona mining in southwestern Wyoming during January-August 2000. (Unless specified otherwise, magnitude implies Richter local magnitude, M{sub L}.) The University of Utah Seismograph Stations (UUSS) undertook this cooperative project to assist the University of California Lawrence Livermore National Laboratory (LLNL) in research and development relating to monitoring the Comprehensive Test Ban Treaty (CTBT). The project, which formally began February 28, 1998, and ended September 1, 2000, had three basic objectives: (1) Strategically install a three-component broadband digital seismic station in the WP-BC region to ensure the continuous recording of high-quality waveform data to meet the long-term needs of LLNL, UUSS, and other interested parties, including the international CTBT community. (2) Determine source mechanisms--to the extent that available source data and resources allowed--for comparative seismic characterization of stress release in mines versus earthquakes in the WP-BC study region. (3) Gather and report to LLNL local information on mine operations and associated seismicity, including ''ground truth'' for significant events. Following guidance from LLNL's Technical Representative, the focus of Objective 2 was changed slightly to place emphasis on three mining-related events that occurred in and near the study area after the original work plan had been made, thus posing new targets of opportunity. These included: a magnitude 3.8 shock that occurred

  4. The seismic signatures of the 2009 Shiaolin landslide in Taiwan

    NASA Astrophysics Data System (ADS)

    Feng, Z.

    2011-05-01

    The Shiaolin landslide occurred on 9 August 2009 after Typhoon Morakot struck Taiwan, claiming over 400 lives. The seismic signals produced by the landslide were recorded by broadband seismic stations in Taiwan. The time-frequency spectra for these signals were obtained by the Hilbert-Huang transform (HHT) and were analyzed to obtain the seismic characteristics of the landslide. Empirical mode decomposition (EMD) was applied to differentiate weak surface-wave signals from noise and to estimate the surface-wave velocities in the region. The surface-wave velocities were estimated using the fifth intrinsic mode function (IMF 5) obtained from the EMD. The spectra of the earthquake data were compared. The main frequency content of the seismic waves caused by the Shiaolin landslide were in the range of 0.5 to 1.5 Hz. This frequency range is smaller than the frequency ranges of other earthquakes. The spectral analysis of surface waves (SASW) method is suggested for characterizing the shear-wave velocities of the strata in the region.

  5. Crustal Thickness Variations Along the Southeastern Caribbean Plate Boundary From Teleseismic and Active Source Seismic Data

    NASA Astrophysics Data System (ADS)

    Bezada, M. J.; Niu, F.; Baldwin, T. K.; Pavlis, G.; Vernon, F.; Rendón, H.; Zelt, C. A.; Schmitz, M.; Levander, A.

    2006-12-01

    Insight into the topography of the Moho discontinuity beneath Venezuela has been progressively gained since the 1990's through seismic refraction studies carried out in the south and east of the country. More recently, both active and passive, land and marine seismic data were acquired by the U.S. BOLIVAR and Venezuelan GEODINOS projects to understand accretion processes and mechanisms for continental growth. The passive component includes an 18-month deployment of 27 PASSCAL broadband seismographs, a 12-month deployment of 15 OBSIP broadband instruments and an ongoing deployment of 8 Rice broadband seismometers. Additionally, data from the 34 BB stations of the national seismic network of Venezuela and the GSN SDV station, give a seismic dataset from 84 stations covering an area of ~750,000 km2. The active component includes 4 onshore-offshore refraction/wide angle reflection profiles as well as the recording of airgun blasts from offshore seismic lines by BB stations in mainland Venezuela and the Leeward Antilles. This abundance of datasets allows us to estimate Moho depths using different methods such as receiver functions, and forward and inverse modeling of wide-angle datasets, but also poses the challenge of reconciling the different values obtained to achieve robust results. Generally the active source and receiver function estimates are close to one another. We present a composite crustal thickness map showing a highly variable crustal thicknesses ranging from 15 km beneath the Caribbean LIP, to ~55 km beneath eastern Venezuela. Crustal thickness is strongly correlated with geologic terranes, but not always as expected. The thickest crust is found to exist in the east of the country, beneath the sedimentary basins north of the Orinoco River where depth to Moho exceeds 50 km. Crustal thickness beneath most of the Precambrian Guayana Shield is fairly constant at ~38 km . In contrast, we observe relatively thin (~25-30 km) crust in the eastern and western

  6. Cooperative Development of the Pakistan Seismic Network System (PSNS)

    NASA Astrophysics Data System (ADS)

    Detweiler, S.; Mooney, W.; McDonald, S.

    2005-12-01

    We propose to cooperate with the Pakistan Meteorological Department for the design and construction of the new Pakistan Seismic Network System (PSNS) that has been funded by the government of Pakistan. The PSNS will consist of 12-15 broadband stations, 50 short-period stations, and 50 accelerometers. Our role will be to provide technical assistance in site selection, to prepare the Request for Proposals (RFP) from industry, and to evaluate performance. The relative importance of tsunami warnings, national earthquake and landslide hazards, and whether a largely urban or truly national network is envisioned will be determined early in the program. Final placement of stations will take many factors into consideration including proximity to faults and seismic activity, geographic accessibility, the consistency of bedrock, and various cultural or social effects. This cooperation has the potential to lead to the development of a desperately needed tsunami early warning network that could protect the Pakistani coastal population in the event of a natural disaster such as the Dec. 26, 2004 Sumatra earthquake and tsunami. The seismic hazard off the coast of Pakistan is high due to the proximity of the Makran and Sumatra subduction zones, the former of which could trigger tsunamis in Pakistan with heights of 12m within minutes. In addition to monitoring earthquake activity, the PSNS will provide seismic data of interest to the world-wide scientific community for a region in which there is little understanding of the upper crust and mantle. It will furthermore address educational outreach and diplomacy issues by providing training to Pakistani scientists in routine network operation and data processing.

  7. The data quality analyzer: A quality control program for seismic data

    NASA Astrophysics Data System (ADS)

    Ringler, A. T.; Hagerty, M. T.; Holland, J.; Gonzales, A.; Gee, L. S.; Edwards, J. D.; Wilson, D.; Baker, A. M.

    2015-03-01

    The U.S. Geological Survey's Albuquerque Seismological Laboratory (ASL) has several initiatives underway to enhance and track the quality of data produced from ASL seismic stations and to improve communication about data problems to the user community. The Data Quality Analyzer (DQA) is one such development and is designed to characterize seismic station data quality in a quantitative and automated manner. The DQA consists of a metric calculator, a PostgreSQL database, and a Web interface: The metric calculator, SEEDscan, is a Java application that reads and processes miniSEED data and generates metrics based on a configuration file. SEEDscan compares hashes of metadata and data to detect changes in either and performs subsequent recalculations as needed. This ensures that the metric values are up to date and accurate. SEEDscan can be run as a scheduled task or on demand. The PostgreSQL database acts as a central hub where metric values and limited station descriptions are stored at the channel level with one-day granularity. The Web interface dynamically loads station data from the database and allows the user to make requests for time periods of interest, review specific networks and stations, plot metrics as a function of time, and adjust the contribution of various metrics to the overall quality grade of the station. The quantification of data quality is based on the evaluation of various metrics (e.g., timing quality, daily noise levels relative to long-term noise models, and comparisons between broadband data and event synthetics). Users may select which metrics contribute to the assessment and those metrics are aggregated into a "grade" for each station. The DQA is being actively used for station diagnostics and evaluation based on the completed metrics (availability, gap count, timing quality, deviation from a global noise model, deviation from a station noise model, coherence between co-located sensors, and comparison between broadband data and synthetics

  8. Data Quality Control of the French Permanent Broadband Network in the RESIF Framework.

    NASA Astrophysics Data System (ADS)

    Grunberg, M.; Lambotte, S.; Engels, F.

    2014-12-01

    In the framework of the RESIF (Réseau Sismologique et géodésique Français) project, a new information system is setting up, allowing the improvement of the management and the distribution of high quality data from the different elements of RESIF. Within this information system, EOST (in Strasbourg) is in charge of collecting real-time permanent broadband seismic waveform, and performing Quality Control on these data. The real-time and validated data set are pushed to the French National Distribution Center (Isterre/Grenoble) to make them publicly available. Furthermore EOST hosts the BCSF-ReNaSS, in charge of the French metropolitan seismic bulletin. This allows to benefit from some high-end quality control based on the national and world-wide seismicity. Here we present the real-time seismic data flow from the stations of the French National Broad Band Network to EOST, and then, the data Quality Control procedures that were recently installed, including some new developments.The data Quality Control consists in applying a variety of processes to check the consistency of the whole system from the stations to the data center. This allows us to verify that instruments and data transmission are operating correctly. Moreover, time quality is critical for most of the scientific data applications. To face this challenge and check the consistency of polarities and amplitudes, we deployed several high-end processes including a noise correlation procedure to check for timing accuracy (intrumental time errors result in a time-shift of the whole cross-correlation, clearly distinct from those due to change in medium physical properties), and a systematic comparison of synthetic and real data for teleseismic earthquakes of magnitude larger than 6.5 to detect timing errors as well as polarity and amplitude problems.

  9. Seismic Response of a Sedimentary Basin: Preliminary Results from Strong Motion Downhole Array in Taipei Basin

    NASA Astrophysics Data System (ADS)

    Young, B.; Chen, K.; Chiu, J.

    2013-12-01

    The Strong Motion Downhole Array (SMDA) is an array of 32 triggered strong motion broadband seismometers located at eight sites in Taipei Basin. Each site features three to five co-located three-component accelerometers--one at the surface and an additional two to four each down independent boreholes. Located in the center of Taipei Basin is Taipei City and the Taipei metropolitan area, the capital of Taiwan and home to more than 7 million residents. Taipei Basin is in a major seismic hazard area and is prone to frequent large earthquakes producing strong ground motion. This unique three-dimension seismic array presents new frontiers for seismic research in Taiwan and, along with it, new challenges. Frequency-dependent and site-specific amplification of seismic waves from depth to surface has been observed: preliminary results indicate that the top few tens of meters of sediment--not the entire thickness--are responsible for significant frequency-dependent amplification; amplitudes of seismic waves at the surface may be as much as seven times that at depth. Dominant amplification frequencies are interpreted as quarter-wavelength constructive interference between the surface and major interfaces in the sediments. Using surface stations with known orientation as a reference, borehole seismometer orientations in these data--which are unknown, and some of which vary considerably from event to event--have been determined using several methods. After low-pass filtering the strong motion data, iteratively rotating the two horizontal components from an individual borehole station and cross-correlating them with that from a co-located surface station has proven to be very effective. In cases where the iterative cross-correlation method does not provide a good fit, rotating both surface and borehole stations to a common axis of maximum seismic energy provides an alternative approach. The orientation-offset of a borehole station relative to the surface station may be

  10. Quantifying the similarity of seismic polarizations

    NASA Astrophysics Data System (ADS)

    Jones, Joshua P.; Eaton, David W.; Caffagni, Enrico

    2016-02-01

    Assessing the similarities of seismic attributes can help identify tremor, low signal-to-noise (S/N) signals and converted or reflected phases, in addition to diagnosing site noise and sensor misalignment in arrays. Polarization analysis is a widely accepted method for studying the orientation and directional characteristics of seismic phases via computed attributes, but similarity is ordinarily discussed using qualitative comparisons with reference values or known seismic sources. Here we introduce a technique for quantitative polarization similarity that uses weighted histograms computed in short, overlapping time windows, drawing on methods adapted from the image processing and computer vision literature. Our method accounts for ambiguity in azimuth and incidence angle and variations in S/N ratio. Measuring polarization similarity allows easy identification of site noise and sensor misalignment and can help identify coherent noise and emergent or low S/N phase arrivals. Dissimilar azimuths during phase arrivals indicate misaligned horizontal components, dissimilar incidence angles during phase arrivals indicate misaligned vertical components and dissimilar linear polarization may indicate a secondary noise source. Using records of the Mw = 8.3 Sea of Okhotsk earthquake, from Canadian National Seismic Network broad-band sensors in British Columbia and Yukon Territory, Canada, and a vertical borehole array at Hoadley gas field, central Alberta, Canada, we demonstrate that our method is robust to station spacing. Discrete wavelet analysis extends polarization similarity to the time-frequency domain in a straightforward way. Time-frequency polarization similarities of borehole data suggest that a coherent noise source may have persisted above 8 Hz several months after peak resource extraction from a `flowback' type hydraulic fracture.

  11. Time functions of deep earthquakes from broadband and short-period stacks

    USGS Publications Warehouse

    Houston, H.; Benz, H.M.; Vidale, J.E.

    1998-01-01

    To constrain dynamic source properties of deep earthquakes, we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic P waves from U.S. National Seismic Network, TERRAscope, and Berkeley Digital Seismic Network broadband stations. We examined 42 earthquakes with depths from 100 to 660 km that occurred between July 1, 1992 and July 31, 1995. To directly compare time functions, or to group them by size, depth, or region, it is essential to scale them to remove the effect of moment, which varies by more than 3 orders of magnitude for these events. For each event we also computed short-period stacks of P waves recorded by west coast regional arrays. The comparison of broadband with short-period stacks yields a considerable advantage, enabling more reliable measurement of event duration. A more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment, producing scaled time functions with both correct timing and amplitude. We find only subtle differences in the broadband time-function shape with moment, indicating successful scaling and minimal effects of attenuation at the periods considered here. The average shape of the envelopes of the short-period stacks is very similar to the average broadband time function. The main variations seen with depth are (1) a mild decrease in duration with increasing depth, (2) greater asymmetry in the time functions of intermediate events compared to deep ones, and (3) unexpected complexity and late moment release for events between 350 and 550 km, with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below. The first two results are broadly consistent with our previous studies, while the third is reported here for the first time. The greater complexity between 350 and 550 km suggests greater heterogeneity in

  12. ORFEUS, a European initiative in broadband seismology: status and future plans

    NASA Astrophysics Data System (ADS)

    van Eck, Torild; Dost, Bernard

    1999-06-01

    Observatories and Research Facilities for European Seismology (ORFEUS) is the European initiative for the coordination of broadband seismology in Europe and the Mediterranean area. The organization is unique in its field, because it does not operate any stations, but acts as an intermediate between data users and data producers. The core activity of ORFEUS is the operation of a data center, which archives seismic waveform data of large seismic events and offers both off-line (CD-ROM) and on-line (Internet, WWW) access to both the archived data and global near real time Spyder® data. ORFEUS coordination function is largely realized through its working groups and web site, which presently provide, among others, station siting and equipment overviews, technical information and support and a Seismological Software Library (SSL). Cooperation with other centers, for example, on data formats, is coordinated through the Federation of Digital Seismograph Networks (FDSN). Future developments emphasize improved data access through the Internet (WWW, Automatic Data Request Manager, NetDC protocol) and a regional version of the Global Spyder®: EuroSpyder. Regularly, work meetings and workshops are organized to discuss future developments and its impact on ORFEUS.

  13. Understanding the Structure of the Subsurface of the El Tatio Geyser field: A Velocity Model of the El Jefe Geyser from Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    LongJohn, T.; Kelly, C.; Seats, K.; Lawrence, J.

    2013-12-01

    Hydrothermal system studies are important for geothermal energy exploration and geysers are also believed to be functional analogues of volcanoes. However, the mechanism of eruption and the characteristics of the plumbing system of most geysers are poorly understood given their subsurface location and sparse global distribution. An accurate acoustic velocity model could yield important insight into subsurface density and thermal variations in a geyser system. Passive seismic data was collected at El Jefe geyser in El Tatio Geyser Field, northern Chile during October of 2012. An array of 6 broadband seismometers and 51 high frequency geophones were deployed for ~1 week in a grid array with station spacing of 2-10 meters (geophones) and 3-50 meters (broadbands) centered around El Jefe Geyser. Using ambient seismic noise generated by the geyser system, I constructed a preliminary subsurface velocity model for El Jefe Geyser. As a result of the close station spacing, the seismic signals sampled shallow depths corresponding to high frequency waves. Coherent seismic records from different seismic station pairs were cross correlated to produce noise correlation functions (NCF). Adaptive covariance filtering and stacking techniques were utilized to amplify the signal of the NCFs and one-dimensional velocities between station pairs at varying depths were determined. Next, a tomographic inversion was done to interpolate between the one-dimensional velocities and produce a three-dimensional velocity model for the entire geyser area. From the velocity model, we can identify regions of low and high acoustic velocity that potentially represent water reservoirs and bedrock respectively.

  14. Local Ambient Seismic Noise Survey in Dixie Valley, NV for Engineered Geothermal System Favorability Assessment

    NASA Astrophysics Data System (ADS)

    Tibuleac, I. M.; Iovenitti, J. L.; von Seggern, D. H.; Sainsbury, J.

    2013-12-01

    The primary objective of this study is to develop and test the seismic component of a calibrated exploration method that integrated geological, geophysical, and geochemical data to identify potential drilling targets for Engineered Geothermal Systems (EGS). In exploring for EGS sites, the selection criteria identified by the AltaRock Energy, Inc. (AltaRock) and University of Nevada, Reno teams are, in order of importance, (1) temperature greater than 200C at 1.5 km depth, (2) rock type at the depth of interest (porous rocks at 1-3 km); and (3) favorable stress regime (tensional environment). To improve spatial resolution, a dense seismic array (21 three-component, broadband sensors, with an overall array aperture of 45km) was installed in two deployments in Dixie Valley, NV, each deployment having a three-month duration Ambient seismic noise and signal were used to retrieve inter-station and same-station Green's Functions (GFs), to be used for subsurface imaging. We used ambient seismic noise interferometry to extract GFs from crosscorrelation of continuous records. An innovative aspect of the seismic work was estimating the receiver functions beneath the stations using noise auto-correlation which was used to image the substructure. We report results of applying the technique to estimate a P/S velocity model from the GF surface wave components and from the GF body-wave reflection component, retrieved from ambient noise and signal cross-correlation and auto-correlation beams. We interpret our results in terms of temperature, pressure and rock composition. The estimated seismic velocity model capability to infer temperature is statistically assessed, in combination with other geophysical technique results.

  15. The Seismic Event in North Korea on 12 May 2010: an assessment from available seismological data

    NASA Astrophysics Data System (ADS)

    Koch, Karl; Kim, Won-Young; Richards, Paul G.; Schaff, David P.

    2016-04-01

    North Korea conducted underground nuclear explosions in October 2006, May 2009, February 2013, and January 2016 that were subsequently officially announced. Based on a number of detections of radionuclides and noble gas elements in May 2010, claims were raised that North Korea conducted a small clandestine nuclear test on its test site on 11 or 12 May 2010, which, however, lacked any signs of an associated seismic event in IMS and non-IMS seismic data. First evidence was presented in fall 2014 and published in February 2015 that data from a Chinese seismic network showed signals that could be related to the claimed underground nuclear explosion in May 2010. Unfortunately, these data have not become openly available for further and wider seismological assessments. First openly available data were found for this seismic event from stations of the North-East China Extended SeiSmic (NECESS) Array consistent with an event on or near the North Korean test site. Later, additional data were obtained from stations of the nearby Dongbei Broadband Seismographic Network (DBSN), for the event of 12 May 2010 and for the underground nuclear tests conducted in 2006 and 2009. Together with data from the open GSN station Mudanjiang (MDJ) in northeastern China we developed a framework for relative location of the event, event characterization by measuring P/S amplitude ratios at different frequencies and by independently assessing the magnitude of the event. While the location of the event can be shown to be within several kilometers of previous nuclear tests, event characterization for frequencies between 5 and 10 Hz indicates that the known nuclear tests are explosion-like; the 12 May 2010 event is in contrast characterized as earthquake-like. Our assessment also indicates that seismic events about three-thousand times smaller than the UNEs in 2013 or 2016 may be monitored on or near the North Korean test site.

  16. Ground motion prediction for the Vienna Basin area using the ambient seismic field

    NASA Astrophysics Data System (ADS)

    Schippkus, Sven; Zigone, Dimitri; Bokelmann, Götz; AlpArray Working Group

    2016-04-01

    The Vienna Basin is one of the most seismically active regions in Austria. Because of the population density and sensitive infrastructure, seismic hazard assessment in this area is of critical importance. An important part of seismic hazard analysis is ground motion prediction, which can in principle be done using either empirical studies to derive ground motion prediction equations (GMPEs) or using a physics-based approach to simulate ground motion by modelling surface wave propagation. Recently a new method has been presented that is based on the emergence of the inter-station Green's function from ambient noise cross-correlations (Denolle et al. 2013), which provides the impulse response of the Earth from a point source at the surface (from the site of one of the two receivers to the other). These impulse responses are dominated by surface waves, which would, in the case of a real earthquake, cause the major damages. The Green's function can in principle be modified to simulate a double couple dislocation at depth, i.e., a virtual earthquake. Using an adapted pre-processing method, the relative amplitudes of the ambient noise records of different inter-station paths are preserved in the correlation functions, and effects like attenuation and amplification of surface waves in sedimentary basins can be studied. This provides more precise information that will help improve seismic hazard evaluations. Here we present a preliminary study of such ground motion prediction for the Vienna Basin using about two dozen broadband stations from available networks in the area, e.g., stations from the University of Vienna (AlpArray) and Vienna Technical University. References Denolle, M. A., E. M. Dunham, G. A. Prieto, and G. C. Beroza (2013), Ground motion prediction of realistic earthquake sources using the ambient seismic field, J. Geophys. Res. Solid Earth, 118, 2102-2118, doi:10.1029/2012JB009603.

  17. A Dramatic Increase in Seismic Observations in the Central and Eastern US

    NASA Astrophysics Data System (ADS)

    Woodward, R.; Busby, R.; Simpson, D.; Alvarez, M.; Vernon, F.

    2009-05-01

    The USArray Transportable Array (TA) is a network of 400 seismograph stations that is systematically moving west-to-east across the contiguous United States. The TA is part of the National Science Foundation's multi- disciplinary EarthScope program. The TA has already occupied over 700 stations in the western US, and is continuing its multi-year migration towards the Atlantic coast before heading for Alaska. The stations use a grid-like deployment with 70 km separation between stations. At any given time there are approximately 400 stations operational, occupying a nominal 800 km by 2000 km "footprint." Each station is operated for two years. TA stations consist of three component broadband seismometers, with a few sites in the westernmost United States also including three component strong motion instruments. The instruments are installed about two meters below the surface, in thermally stable vaults. All stations transmit continuous data in near-real-time, and the data are freely distributed through the IRIS Data Management Center. TA stations can be upgraded to incorporate high frequency or strong motion instrument. Organizations can also "adopt" stations after installation by reimbursing the cost of the hardware, so that the stations become permanent. The TA is presently operating in the swath of the country extending from Texas to Montana. From 2010 to 2013 the TA will occupy ~800 sites in the central and eastern US. The array will be centered on the New Madrid, MO region during the bicentennial of the 1811-1812 earthquakes. During the TA deployment every existing or planned nuclear plant in the eastern US will be within 70 km of at least four new seismic stations. Thus, this station deployment in the eastern half of the US presents an unprecedented opportunity for improving source characterization, modeling the regional velocity and attenuation structure, and mapping seismic zones down to low magnitude thresholds. We will provide an overview of TA

  18. Bimodal Seismic Anisotropy at Cotopaxi volcano (Ecuador): Possible implications

    NASA Astrophysics Data System (ADS)

    Amin Douillet, Guilhem; Ruiz, Mario; Robin, Claude

    2010-05-01

    A shear wave splitting analysis was performed on Cotopaxi volcano, one of Ecuador most active and hazardous volcanoes, in order to investigate the stress state under this volcano. Cotopaxi volcano is located in a highly populated area including the capital Quito. It's eruptive cycle is approximately 120 ±70 years and apart from possible minor eruptions in 1942 and 1903-1904, the last volcanic activity dates from 1878-1885. Moreover, 15 years of increasing seismicity with some major crisis during the 1995-2010 periods, lead to the current very high seismic level. Finally two years of gas monitoring suggest that the Cotopaxi's emissions are currently intermittent and passive, but non negligible. We analyzed 102 regional tectonic events recorded between 2006 and 2009 at a network of five broad-band three-component seismic stations. These stations are located on all flanks of Cotopaxi. The events used were from several seismic sources located inside a radius of 200 kilometers from the volcano and illuminate all space directions. Seismic events were manually chosen based on their clear shear wave component in regards to the compression wave and to the noise. The data were computed using Matlab software. Polarization directions and delay times of split shear waves were found using a method based on the cross correlation of displacement waveforms of shear-waves at all possible rotation angles. Our results show a bimodal anisotropic behavior. One of the fast-directions axes follows the regional Ecuadorian tectonic general strain with a ESE direction. The other trend was found to be perpendicular to the regional strain. Other studies have shown that a 90° flip may take place either prior, during, or just after the main eruptive phase, or during hydraulic injections. This 90° flip is probably relied to micro cracks filling and pressuring, creating a local reverse strain field. There is not clear trend on temporal evolution of anisotropy distribution on our data. Only one

  19. Hybrid Simulations of the Broadband Ground Motions for the 2008 MS8.0 Wenchuan, China, Earthquake

    NASA Astrophysics Data System (ADS)

    Yu, X.; Zhang, W.

    2012-12-01

    The Ms8.0 Wenchuan earthquake occurred on 12 May 2008 at 14:28 Beijing Time. It is the largest event happened in the mainland of China since the 1976, Mw7.6, Tangshan earthquake. Due to occur in the mountainous area, this great earthquake and the following thousands aftershocks also caused many other geological disasters, such as landslide, mud-rock flow and "quake lakes" which formed by landslide-induced reservoirs. These resulted in tremendous losses of life and property. Casualties numbered more than 80,000 people, and there were major economic losses. However, this earthquake is the first Ms 8 intraplate earthquake with good close fault strong motion coverage. Over four hundred strong motion stations of the National Strong Motion Observation Network System (NSMONS) recorded the mainshock. Twelve of them located within 20 km of the fault traces and another 33 stations located within 100 km. These observations, accompanying with the hundreds of GPS vectors and multiple ALOS INSAR images, provide an unprecedented opportunity to study the rupture process of such a great intraplate earthquake. In this study, we calculate broadband near-field ground motion synthetic waveforms of this great earthquake using a hybrid broadband ground-motion simulation methodology, which combines a deterministic approach at low frequencies (f < 1.0 Hz) with a theoretic Green's function calculation approach at high frequency ( ~ 10.0 Hz). The fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed, and rise time that were obtained by an inversion kinematic source model. At the same time, based on the aftershock data, we analyze the site effects for the near-field stations. Frequency-dependent site-amplification values for each station are calculated using genetic algorithms. For the calculation of the synthetic waveforms, at first, we carry out simulations using the hybrid methodology for the frequency up to 10.0 Hz. Then, we consider for

  20. Romanian Data Center: A modern way for seismic monitoring

    NASA Astrophysics Data System (ADS)

    Neagoe, Cristian; Marius Manea, Liviu; Ionescu, Constantin

    2014-05-01

    The main seismic survey of Romania is performed by the National Institute for Earth Physics (NIEP) which operates a real-time digital seismic network. The NIEP real-time network currently consists of 102 stations and two seismic arrays equipped with different high quality digitizers (Kinemetrics K2, Quanterra Q330, Quanterra Q330HR, PS6-26, Basalt), broadband and short period seismometers (CMG3ESP, CMG40T, KS2000, KS54000, KS2000, CMG3T,STS2, SH-1, S13, Mark l4c, Ranger, gs21, Mark l22) and acceleration sensors (Episensor Kinemetrics). The data are transmitted at the National Data Center (NDC) and Eforie Nord (EFOR) Seismic Observatory. EFOR is the back-up for the NDC and also a monitoring center for the Black Sea tsunami events. NIEP is a data acquisition node for the seismic network of Moldova (FDSN code MD) composed of five seismic stations. NIEP has installed in the northern part of Bulgaria eight seismic stations equipped with broadband sensors and Episensors and nine accelerometers (Episensors) installed in nine districts along the Danube River. All the data are acquired at NIEP for Early Warning System and for primary estimation of the earthquake parameters. The real-time acquisition (RT) and data exchange is done by Antelope software and Seedlink (from Seiscomp3). The real-time data communication is ensured by different types of transmission: GPRS, satellite, radio, Internet and a dedicated line provided by a governmental network. For data processing and analysis at the two data centers Antelope 5.2 TM is being used running on 3 workstations: one from a CentOS platform and two on MacOS. Also a Seiscomp3 server stands as back-up for Antelope 5.2 Both acquisition and analysis of seismic data systems produce information about local and global parameters of earthquakes. In addition, Antelope is used for manual processing (event association, calculation of magnitude, creating a database, sending seismic bulletins, calculation of PGA and PGV, etc.), generating

  1. Seismic velocity change and slip rate during the 2006 Guerrero (Mexico) slow slip event

    NASA Astrophysics Data System (ADS)

    Rivet, Diane; Radiguet, Mathilde; Campillo, Michel; Cotton, Fabrice; Shapiro, Nikolai; Krishna Singh, Shri; Kostoglodov, Vladimir

    2010-05-01

    We measure temporal change of the seismic velocity in the crust below the Guerrero region during the 2006 slow sleep event (SSE). We use repeated cross-correlations of ambient seismic noise recorded at 26 broad-band stations of the MesoAmerica Seismic Experiment (MASE). The cross-correlations are computed over 90 days with a moving window of 10 days from January 2005 to July 2007. To insure measurements independent of noise source variations, we only take into account the travel time change within the coda. For period of 8 to 20s, we observe a decrease in velocity starting in April 2006 with a maximum change of -0.3% of the initial velocity in June 2006. At these periods, the Rayleigh waves are sensitive to velocity changes down to the lower crust. In the other hand, we compute the deformation rate below the MASE array from a slip propagation model of the SSE observed by means of the displacement time-series of 15 continuous GPS stations. Slip initiates in the western part of the Guerrero Gap and propagates southeastward. The propagation velocity is of the order of 1 km/day. We then compare the seismic velocity change measured from continuous seismological data with the deformation rate inferred from geodetic measurements below the MASE array. We obtain a good agreement between the time of maximal seismic velocity change (July 2006) and the time of maximum deformation associated with the SSE (July to August 2006). This result shows that the long-term velocity change associated with the SSE can be detected using continuous seismic recordings. Since the SSE does not emit seismic waves, which interact with the superficial layers, the result indicates that the velocity change is due to deformation at depth.

  2. Passive seismic monitoring studies at Tiris geothermal field in East Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Jaya, Makky; Jousset, Philippe; Deon, Fiorenza; Gassner, Alexandra; Putriatni, Dewi; Supoyo, Supoyo; Suprianto, Agus; Putra, Tri; Erbas, Kemal

    2013-04-01

    The Tiris geothermal field (TGF) is indicated by the presence of two sets of surface warm springs located within the proximity of two volcanoes: Mt. Lamongan and Mt. Argopuro. Preliminary assessment of TGF in terms of petrology of the volcanic rock and geochemistry of springs has been studied by Deon et al. (2012). The combination of petrology and geochemistry studies suggests: 1) the relation between sea water and the origin of warm springs and 2) the existence of a concealed layer responsible for capturing H2S gas which, in turn, accounts to the observed HCO3- excess of the springs. In order to support hypotheses resulting from those petrology and geochemistry studies, two passive seismic field experiments have been deployed successively. The first small-scale seismic noise study in 2011 was carried out by setting up 5 geophones for 5-days monitoring positioned around Mt. Lamongan. The second larger-scale passive seismic study has been performed since October 2012 setting up 16 short period stations and 4 broad-band stations around TGF for 6 months monitoring period. The goal of preliminary seismic noise test in 2011 was to identify pre-dominant noise characteristics in the area, while passive seismic monitoring in 2012 attempts to reveal the underground geologic structure of TGF derived from seismic properties. We report the set-up of both experiments and describe first result of seismic noise analysis and preliminary monitoring analysis. References Deon, F.; Moeck, I.; Scheytt, T.; Jaya, M.S. (2012): Preliminary assessment of the geothermal system of the Tiris colcanic area, East Java, Indonesia. 74th EAGE Conference & Exhibition (Copenhagen, Denmark 2012).

  3. Map of Pseudo-F-statistics of seismic noise parameters as an indicator of current seismic danger in Japan

    NASA Astrophysics Data System (ADS)

    Lyubushin, Alexey

    2016-04-01

    The problem of estimate of current seismic danger based on monitoring of seismic noise properties from broadband seismic network F-net in Japan (84 stations) is considered. Variations of the following seismic noise parameters are analyzed: multifractal singularity spectrum support width, generalized Hurst exponent, minimum Hölder-Lipschitz exponent and minimum normalized entropy of squared orthogonal wavelet coefficients. These parameters are estimated within adjacent time windows of the length 1 day for seismic noise waveforms from each station. Calculating daily median values of these parameters by all stations provides 4-dimensional time series which describes integral properties of the seismic noise in the region covered by the network. Cluster analysis is applied to the sequence of clouds of 4-dimensional vectors within moving time window of the length 365 days with mutual shift 3 days starting from the beginning of 1997 up to the current time. The purpose of the cluster analysis is to find the best number of clusters (BNC) from probe numbers which are varying from 1 up to the maximum value 40. The BNC is found from the maximum of pseudo-F-statistics (PFS). A 2D map could be created which presents dependence of PFS on the tested probe number of clusters and the right-hand end of moving time window which is rather similar to usual spectral time-frequency diagrams. In the paper [1] it was shown that the BNC before Tohoku mega-earthquake on March 11, 2011, has strongly chaotic regime with jumps from minimum up to maximum values in the time interval 1 year before the event and this time intervals was characterized by high PFS values. The PFS-map is proposed as the method for extracting time intervals with high current seismic danger. The next danger time interval after Tohoku mega-EQ began at the end of 2012 and was finished at the middle of 2013. Starting from middle of 2015 the high PFS values and chaotic regime of BNC variations were returned. This could be

  4. An Unusual Cluster of Low-Frequency Earthquakes at Mount Baker, Washington, as Detected by a Local Broadband Network

    NASA Astrophysics Data System (ADS)

    Caplan-Auerbach, J.; Thelen, W. A.; Moran, S. C.

    2009-12-01

    A recent cluster of shallow low-frequency earthquakes on Mount Baker volcano marks one of the most seismically active periods in the volcano’s instrumented history (since 1972). Although Mount Baker, the northernmost of the U. S. Cascade volcanoes, has a history of recorded unrest (including an episode of geothermal unrest in 1975-6), it has never exhibited high levels of seismicity. Most of Baker’s seismicity has been associated with glacial earthquakes and deep long-period events. However, between June and September 2009 at least 39 low-frequency events were recorded at Mount Baker, 21 of which were located by the Pacific Northwest Seismic Network (PNSN). Locations are shallow and are scattered over a 5 x 5 km area around the southwest flank of the edifice. However, waveform similarity between many events suggests that most are located fairly close together and that the scatter apparent in PNSN locations is largely because of picking errors and a sparse network. To better constrain earthquake locations and source mechanism, a network of five broadband seismometers was deployed on Mount Baker between July and October 2009. This network greatly reduced the magnitude threshold for locatable events, with approximately three times as many earthquakes located by the local network than with the existing regional network. The additional stations also provided better depth constraints. The local network detected a larger number of events than identical temporary networks deployed in 2007 and 2008, suggesting that the increase in seismicity is real. Earthquakes located with the addition of data from the local network still locate at shallow depths beneath the southwest flank, but location uncertainty is significantly improved. We are using waveform similarity to evaluate relative event locations and investigate possible source mechanisms for the earthquakes, and are developing a more accurate velocity model that includes station elevations. This will better determine

  5. Investigation of Seismic Events Associated with the Sinkhole at Napoleonville Salt Dome, Louisiana

    NASA Astrophysics Data System (ADS)

    Nayak, A.; Dreger, D. S.

    2014-12-01

    This study describes the ongoing efforts in analysis of the intense sequence of complex seismic events associated with the formation of a large sinkhole at Napoleonville Salt Dome, Assumption Parish, Louisiana in August 2012. We investigate source mechanisms of these events, represented by a general 2nd order point source centroid seismic moment tensor (MT) using data from a temporary network of broadband stations established by the United States Geological Survey. We have implemented a grid-search technique to detect and compute the centroid hypocenter and MT solution of events using low frequency (0.1-0.3 Hz) 25-second duration displacement waveforms and 1D velocity models for the salt dome and the surrounding sediment sequence. Application of this technique to data extending up to 17 days before and after the appearance of the sinkhole yields a catalog of > 1200 events. We describe the evolution of the seismicity in time with respect to hypocenters, source-types, and magnitudes. We also examine the Gutenberg-Richter statistics and relationship between inter-event times and magnitudes. Since fewer stations were operational during the time period preceding the appearance of the sinkhole, we perform various sensitivity tests to examine the effects of decrease in station coverage from a 5-station network to a 3-station network on location, source-type and magnitude uncertainties. We also apply a finite source MT inversion approach using grid-search to isolate specific larger-magnitude events that occur in rapid succession resulting in overlapping waveforms. The MT analysis is supplemented by a separate waveform cross-correlation analysis to study smaller magnitude events that have poor signal-to-noise ratios at low frequencies. We also explore the role of fluids, possible a natural gas-water mixture, in the spectral peaks observed in the seismic signals.

  6. Borehole Water Level Measurements in Kamchatka and Broadband Records of Very Large (M≧7.6) Earthquakes

    NASA Astrophysics Data System (ADS)

    Kasimova, V.; Kopylova, G.

    2010-12-01

    The impact of seismic waves from distant very large earthquakes can be accompanied by various changes in the groundwater mode. Such effects are observed at distances up to thousands of kilometers from the epicenter and indicate a change in the stress-strain state of geological environment. One of the methods of geophysical monitoring of seismically active regions is the water level observations in the boreholes. Different variations of water level caused by the passage of seismic waves from the very large earthquakes are recorded in piezometric boreholes in Kamchatka. In connection with the very large earthquakes it was observed four types of variations of water level in borehole UZ-5 (Kamchatka, Russia). To quantify the impact of the characteristics of seismic waves on the state of groundwater can be used assess the amplitude and frequency of maximum phase ground motion (velocity, displacement and acceleration) according to the registration of seismic signals of broadband seismic instrumentation. The purpose of this study is to determine the dependence of expression of different types of variations of water level in borehole UZ-5 from the amplitude and frequency of seismic signals from the very large earthquakes recorded by IRIS seismic equipment on the seismic station Petropavlovsk (s/s PET). We used records of earthquakes since 1997, M≧7.6 and 10-minute data of water level meter observations on the borehole UZ-5. Analysis of seismic signals in the time and frequency-time domain with the assessment times, amplitudes and periods of maximum oscillation phases was carried out using the interactive software DIMAS. The restoration of initial ground motion (displacement, acceleration) was carried out. The evaluation of amplitudes and frequency content of maximum oscillation phases of ground and the comparison with the variations of water level in the hole UZ-5 was executed. Dependences of the amplitude-frequency content of maximum oscillation phases of ground

  7. How a Country-Wide Seismological Network Can Improve Understanding of Seismicity and Seismic Hazard -- The Example of Bhutan

    NASA Astrophysics Data System (ADS)

    Hetényi, G.; Diehl, T.; Singer, J.; Kissling, E. H.; Clinton, J. F.; Wiemer, S.

    2015-12-01

    The Eastern Himalayas are home to a seemingly complex seismo-tectonic evolution. The rate of instrumental seismicity is lower than the average along the orogen, there is no record of large historical events, but both paleoseismology and GPS studies point to potentially large (M>8) earthquakes. Due to the lack of a permanent seismic monitoring system in the area, our current level of understanding is inappropriate to create a reliable quantitative seismic hazard model for the region. Existing maps are based on questionable hypotheses and show major inconsistencies when compared to each other. Here we present results on national and regional scales from a 38-station broadband seismological network we operated for almost 2 years in the Kingdom of Bhutan. A thorough, state-of-the-art analysis of local and regional earthquakes builds a comprehensive catalogue that reveals significantly (2-to-3 orders of magnitude) more events than detected from global networks. The seismotectonic analysis reveals new patterns of seismic activity as well as striking differences over relatively short distances within the Himalayas, only partly explained by surface observations such as geology. We compare a priori and a posteriori (BMC) magnitude of completeness maps and show that our network was able to detect all felt events during its operation. Some of these events could be felt at surprisingly large distances. Based on our experiment and experience, we draft the pillars on which a permanent seismological observatory for Bhutan could be constructed. Such a continuous monitoring system of seismic activity could then lead to a reliable quantitative seismic hazard model for Bhutan and surrounding regions, and serve as a base to improve building codes and general preparedness.

  8. Crustal structure of the Altiplano from broadband regional waveform modeling: Implications for the composition of thick continental crust

    NASA Astrophysics Data System (ADS)

    Swenson, Jennifer L.; Beck, Susan L.; Zandt, George

    2000-01-01

    We have modeled the full waveforms from six intermediate-depth and two shallow earthquakes recorded at regional distances by the BANJO Broadband Andean Joint Experiment (BANJO) and Seismic Exploration of the Deep Altiplano (SEDA) portable seismic networks in the central Andes. In this study we utilize data from those BANJO and SEDA stations located within the Altiplano and Eastern Cordillera. We used reflectivity synthetic seismograms and a grid search to constrain four parameters of the Altiplano-Eastern Cordillera lithosphere: crustal thickness, average crustal velocity (Vp), and crustal and upper mantle Poisson's ratios (σcrust and σmantle). Using our grid search, we investigated the crustal and upper mantle structure along 36 individual event station paths and applied forward modeling to 56 event station paths. Robust models for the Altiplano that provide the best overall fit between the data and synthetic seismograms are characterized by an average Vp of 5.75-6.25 km/s, crustal thicknesses of 60-65 km, σcrust = 0.25, and σmantle = 0.27-0.29. We find a north-south variation in the structure of the Altiplano, with the crust south of the BANJO transect characterized by either lower than average crustal P wave velocities or a slightly higher σcrust relative to crust north of the BANJO transect. These results are consistent with a model of crustal thickening caused predominantly by tectonic shortening of felsic crust, rather than by underplating or magmatic intrusion from the mantle.

  9. Automated inter-station phase velocity measurements across the eastern Mediterranean and Middle East

    NASA Astrophysics Data System (ADS)

    El-Sharkawy, Amr; Weidle, Christian; Christiano, Luigia; Soomro, Riaz; Lebedev, Sergi; Meier, Thomas

    2016-04-01

    The structure of the lithosphere in northeastern Africa, eastern Mediterranean and the Middle East is highly variable. It ranges from young oceanic lithosphere in the Red Sea to what is considered the oldest oceanic lithosphere on Earth in the Mediterranean Sea north of Libya, and from highly deformed continental lithosphere at the east-Mediterranean margins to more stable continental lithosphere of Phanerozoic origin and to cratonic lithosphere beneath the Arabian Peninsula. Details of the lithospheric structure are, however, poorly known. Surface waves are ideally suited for studies of the lithosphere and the sublithospheric mantle. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by surface wave tomography. Using regional to teleseismic Rayleigh and Love waves that traverse the area we can obtain information about its seismic structure by examining phase velocities as a function of frequency. A newly developed algorithm for automated inter-station phase velocity measurements (Soomro et al. 2016) is applied here to obtain both Rayleigh and Love fundamental mode phase velocities. We utilize a database consisting of more than 3800 regional and teleseismic earthquakes recorded by more than 1850 broadband seismic stations within the area, provided by the European Integrated Data Archive (WebDc/EIDA) and IRIS. Moreover, for the first time, data from the Egyptian National Seismological Network (ENSN), recorded by up to 25 broad band seismic stations, is also included in the analysis. For each station pair approximately located on the same great circle path, the recorded waveforms are cross correlated and the dispersion curves of fundamental modes are calculated from the phase of the weighted cross correlation functions. Path average dispersion curves are obtained by averaging the smooth parts of single-event dispersion curves. Parameters tests and preliminary results of automatically measured phase velocities are

  10. Locating and Modeling Regional Earthquakes with Broadband Waveform Data

    NASA Astrophysics Data System (ADS)

    Tan, Y.; Zhu, L.; Helmberger, D.

    2003-12-01

    Retrieving source parameters of small earthquakes (Mw < 4.5), including mechanism, depth, location and origin time, relies on local and regional seismic data. Although source characterization for such small events achieves a satisfactory stage in some places with a dense seismic network, such as TriNet, Southern California, a worthy revisit to the historical events in these places or an effective, real-time investigation of small events in many other places, where normally only a few local waveforms plus some short-period recordings are available, is still a problem. To address this issue, we introduce a new type of approach that estimates location, depth, origin time and fault parameters based on 3-component waveform matching in terms of separated Pnl, Rayleigh and Love waves. We show that most local waveforms can be well modeled by a regionalized 1-D model plus different timing corrections for Pnl, Rayleigh and Love waves at relatively long periods, i.e., 4-100 sec for Pnl, and 8-100 sec for surface waves, except for few anomalous paths involving greater structural complexity, meanwhile, these timing corrections reveal similar azimuthal patterns for well-located cluster events, despite their different focal mechanisms. Thus, we can calibrate the paths separately for Pnl, Rayleigh and Love waves with the timing corrections from well-determined events widely recorded by a dense modern seismic network or a temporary PASSCAL experiment. In return, we can locate events and extract their fault parameters by waveform matching for available waveform data, which could be as less as from two stations, assuming timing corrections from the calibration. The accuracy of the obtained source parameters is subject to the error carried by the events used for the calibration. The detailed method requires a Green­_s function library constructed from a regionalized 1-D model together with necessary calibration information, and adopts a grid search strategy for both hypercenter and

  11. A seismic network to investigate the sedimentary hosted hydrothermal Lusi system

    NASA Astrophysics Data System (ADS)

    Javad Fallahi, Mohammad; Mazzini, Adriano; Lupi, Matteo; Obermann, Anne; Karyono, Karyono

    2016-04-01

    The 29th of May 2006 marked the beginning of the sedimentary hosted hydrothermal Lusi system. During the last 10 years we witnessed numerous alterations of the Lusi system behavior that coincide with the frequent seismic and volcanic activity occurring in the region. In order to monitor the effect that the seismicity and the activity of the volcanic arc have on Lusi, we deployed a ad hoc seismic network. This temporary network consist of 10 broadband and 21 short period stations and is currently operating around the Arjuno-Welirang volcanic complex, along the Watukosek fault system and around Lusi, in the East Java basin since January 2015. We exploit this dataset to investigate surface wave and shear wave velocity structure of the upper-crust beneath the Arjuno-Welirang-Lusi complex in the framework of the Lusi Lab project (ERC grant n° 308126). Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group and phase velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions, and are tomographically inverted to provide 2D velocity maps corresponding to different sampling depths. 3D shear wave velocity structure is then acquired by inverting the group velocity maps.

  12. Features of seismicity of the Euro-Arctic region

    NASA Astrophysics Data System (ADS)

    Rogozhin, E. A.; Antonovskaya, G. N.; Kapustian, N. K.; Fedorenko, I. V.

    2016-04-01

    New results from seismic monitoring in the Euro-Arctic region, including the seismicity of Gakkel Ridge and the Barents-Kara Sea shelf, are presented. The data used were obtained from the Arkhan-gelsk seismic network. The role of island-based seismic stations, in particular, those in Franz Josef Land, in the monitoring network is discussed. The possibility of specifying the nature of seismicity by waveform spectral-temporal analysis, even in the case of a single station, is considered.

  13. Seismic instrumentation plan for the Hawaiian Volcano Observatory

    USGS Publications Warehouse

    Thelen, Weston A.

    2014-01-01

    The installation of new seismic stations is only the first part of building a volcanic early warning capability for seismicity in the State of Hawaii. Additional personnel will likely be required to study the volcanic processes at work under each volcano, analyze the current seismic activity at a level sufficient for early warning, build new tools for monitoring, maintain seismic computing resources, and maintain the new seismic stations.

  14. Tomographic Imaging of the Magmatic System at Mount St. Helens with the iMUSH Broadband Array

    NASA Astrophysics Data System (ADS)

    Ulberg, C. W.; Creager, K. C.; Levander, A.; Kiser, E.; Moran, S. C.; Abers, G. A.; Schmandt, B.; Vidale, J. E.; Houston, H.; Denlinger, R. P.; Williams, M. C. B.

    2015-12-01

    We deployed 70 broadband seismometers in the summer of 2014 to image the velocity structure beneath Mount St. Helens (MSH), Washington, USA as part of a collaborative project called imaging Magma Under St. Helens (iMUSH). Our goal is to illuminate the MSH magmatic system, using active- and passive-source seismology, magnetotellurics and petrology. Details of the velocity structure, coupled with other geophysical and geologic data, can help constrain the geometry and physical state of any bodies of melt beneath the volcano. The broadband array has a diameter of ~100 km centered on MSH with an average station spacing of 10 km, and will remain deployed through summer 2016. It is augmented by dozens of permanent stations in the area. We determine P-wave arrival times using Antelope software and incorporate permanent network picks for the region. We use the program struct3DP to invert travel times to obtain a 3-D seismic velocity model and relocate hypocenters, computing travel times using a 3-D eikonal-equation solver. There were more than 500 useable local events during the first year of iMUSH broadband recording, which to date have provided 5000 arrival times, with the number growing rapidly. The local events include 23 active shots that were set off in the summer of 2014 as part of the iMUSH experiment, which recorded with good signal-to-noise ratios across the entire array. The absolute P times will be augmented by differential times calculated by cross-correlation between observations at the same station for nearby event pairs. These will be incorporated into our model using double-difference tomography. We anticipate that our 3D velocity model will provide the highest resolution image of volcanic plumbing at MSH thus far. Our model interpretation will incorporate results from active-source and ambient noise tomography, receiver functions, magnetotellurics, and petrology.

  15. Source Mechanism of May 30, 2015 Bonin Islands, Japan Deep Earthquake (Mw7.8) Estimated by Broadband Waveform Modeling

    NASA Astrophysics Data System (ADS)

    Tsuboi, S.; Nakamura, T.; Miyoshi, T.

    2015-12-01

    May 30, 2015 Bonin Islands, Japan earthquake (Mw 7.8, depth 679.9km GCMT) was one of the deepest earthquakes ever recorded. We apply the waveform inversion technique (Kikuchi & Kanamori, 1991) to obtain slip distribution in the source fault of this earthquake in the same manner as our previous work (Nakamura et al., 2010). We use 60 broadband seismograms of IRIS GSN seismic stations with epicentral distance between 30 and 90 degrees. The broadband original data are integrated into ground displacement and band-pass filtered in the frequency band 0.002-1 Hz. We use the velocity structure model IASP91 to calculate the wavefield near source and stations. We assume that the fault is squared with the length 50 km. We obtain source rupture model for both nodal planes with high dip angle (74 degree) and low dip angle (26 degree) and compare the synthetic seismograms with the observations to determine which source rupture model would explain the observations better. We calculate broadband synthetic seismograms with these source propagation models using the spectral-element method (Komatitsch & Tromp, 2001). We use new Earth Simulator system in JAMSTEC to compute synthetic seismograms using the spectral-element method. The simulations are performed on 7,776 processors, which require 1,944 nodes of the Earth Simulator. On this number of nodes, a simulation of 50 minutes of wave propagation accurate at periods of 3.8 seconds and longer requires about 5 hours of CPU time. Comparisons of the synthetic waveforms with the observation at teleseismic stations show that the arrival time of pP wave calculated for depth 679km matches well with the observation, which demonstrates that the earthquake really happened below the 660 km discontinuity. In our present forward simulations, the source rupture model with the low-angle fault dipping is likely to better explain the observations.

  16. Seismic Observations on Greenland Ice Sheet By a Joint USA and Japanese Glisn Team (2011-2014)

    NASA Astrophysics Data System (ADS)

    Toyokuni, G.; Kanao, M.; Tono, Y.; Himeno, T.; Tsuboi, S.; Childs, D.; Dahl-Jensen, T.; Anderson, K. R.

    2014-12-01

    Global climate change is currently causing melting of the Greenland ice sheet. Recently, a new type of seismic event, referred to as a "glacial earthquake", has been recognized. Such earthquakes are generated by the movements of large masses of ice within the terminal regions of glacier, and represent a new approach for monitoring ice sheet dynamics. In 2009, the GreenLand Ice Sheet monitoring Network (GLISN) was initiated as international project to monitor changes in ice sheet by constructing a large broadband seismological network in and around Greenland. Japan is a partner country from when the GLISN project was launched, and has been sending an expedition team every year from 2011. In 2011, the Japanese GLISN team, together with the USA team, installed the dual seismic-GPS station ICESG-GLS2 in the middle of the Greenland ice cap. In 2012 and 2013, we performed maintenance at the ICESG-GLS2, DY2G-GLS1, and NUUK stations. In August 2014, we plan to participate in maintenance operations on three dual seismic-GPS stations on ice (ICESG-GLS2, DY2G-GLS1, and NEEM-GLS3), as well as two stations on bedrock at East coast (DBG and SOEG). This presentation will summarize our field activities for four years, and show results from preliminary analysis with the retrieved data. The Japanese GLISN team has been supported by JSPS KAKENHI 24403006.

  17. Earthquake Detection and Location Capabilities of the Advanced National Seismic Network

    NASA Astrophysics Data System (ADS)

    McNamara, D. E.; Buland, R. P.; Benz, H. M.; Leith, W.

    2004-12-01

    We have computed minimum earthquake moment magnitude, Mw, detection thresholds for a 1x1 degree grid across the US using the existing backbone stations of the Advanced National Seismic System (ANSS). For every grid point we compute the minimum Mw for which the P phase should be detectable by at least five ANSS stations. Detection is declared at a station when body wave power levels produced for a given Mw are above the frequency dependent 80th percentile noise level for the station. Noise levels were determined in a previous study from probability density functions of noise spectra computed for each ANSS backbone station (McNamara and Buland, 2004). To model event power levels, earthquake moment, Mo, is computed as a function of apparent corner frequency using the source scaling formulas of Brune (1970, 1971). The apparent corner frequency is the frequency at which body wave spectral amplitudes are maximum as a result of attenuation and short period filters applied during NEIC phase picking. The corresponding moment magnitude, Mw, is computed after Kanamori (1977). Body wave amplitudes are then computed for each station depending on the distance and attenuation along each raypath. Amplitude is then converted to power (dB) and compared to station noise levels. The fifth lowest power, above station noise levels then corresponds to the minimum earthquake magnitude for that particular grid point. Our theoretical minimum Mw threshold compares favorably to magnitude thresholds determined from USGS PDE catalogs. We also model the regional variation in event location improvement with the installation of planned ANSS backbone stations. Results from this study are useful for characterizing the performance of existing ANSS broadband stations, for detecting operational problems, and should be relevant to the future siting of ANSS backbone stations. Results from this analysis are also used to optimize the distribution of ANSS regional network stations.

  18. Romanian Complex Data Center for Dense Seismic network

    NASA Astrophysics Data System (ADS)

    Neagoe, Cristian; Ionescu, Constantin; Marius Manea, Liviu

    2010-05-01

    Since 2002 the National Institute for Earth Physics (NIEP) developed its own real-time digital seismic network: consisting of 96 seismic stations of which 35 are broadband sensors and 24 stations equipped with short period sensors and two arrays earthquakes that transmit data in real time at the National Data Center (NDC) and Eforie Nord (EFOR) Seismic Observatory. EFOR is the back-up for the NDC and also a monitoring center for Black Sea tsunamis. Seismic stations are equipped with Quanterra Q330 and K2 digitizers, broadband seismometers (STS2, CMG40T, CMG 3ESP, CMG3T) and acceleration sensors Episensor Kinemetrics (+ / - 2G). SeedLink who is a part of Seiscomp2.5 and Antelope are software packages used for acquisition in real time (RT) and for data exchange. Communication of digital seismic stations to the National Data Center in Bucharest and Seismic Observatory Eforie Nord is assured by 5 providers (GPRS, VPN, satellite radio and Internet communication). For acquisition and data processing at the two centers of reception and processing is used AntelopeTM 4.11 running on 2 workstations: one for real-time and other for offline processing and also a Seiscomp 3 server that works as back-up for Antelope 4.11 Both acquisition and analysis of seismic data systems produced information about local and global parameters of earthquakes, in addition Antelope is used for manual processing (association events, the calculation of magnitude, creating a database, sending seismic bulletins, calculation of PGA and PGV , etc.), generating ShakeMap products and interacts with global data centers. In order to make all this information easily available across the Web and also lay the grounds for a more modular and flexible development environment the National Data Center developed tools to enable centralizing of data from software such as Antelope which is using a dedicated database system ( Datascope, a database system based on text files ) to a more general-purpose database, My

  19. Pacific Array (Transportable Broadband Ocean Floor Array)

    NASA Astrophysics Data System (ADS)

    Kawakatsu, Hitoshi; Ekstrom, Goran; Evans, Rob; Forsyth, Don; Gaherty, Jim; Kennett, Brian; Montagner, Jean-Paul; Utada, Hisashi

    2016-04-01

    Based on recent developments on broadband ocean bottom seismometry, we propose a next generation large-scale array experiment in the ocean. Recent advances in ocean bottom broadband seismometry1, together with advances in the seismic analysis methodology, have enabled us to resolve the regional 1-D structure of the entire lithosphere/asthenosphere system, including seismic anisotropy (azimuthal, and hopefully radial), with deployments of ~15 broadband ocean bottom seismometers (BBOBSs). Having ~15 BBOBSs as an array unit for a 2-year deployment, and repeating such deployments in a leap-frog way or concurrently (an array of arrays) for a decade or so would enable us to cover a large portion of the Pacific basin. Such efforts, not only by giving regional constraints on the 1-D structure beneath Pacific ocean, but also by sharing waveform data for global scale waveform tomography, would drastically increase our knowledge of how plate tectonics works on this planet, as well as how it worked for the past 150 million years. International collaborations is essential: if three countries/institutions participate this endeavor together, Pacific Array may be accomplished within five-or-so years.

  20. Search for solar normal modes in low-frequency seismic spectra

    NASA Astrophysics Data System (ADS)

    Caton, Ross C.

    We use seismic array processing methods to attempt to enhance very low frequency harmonic signals (0-400 microhertz, also ?Hz or uHz) recorded on broadband seismic arrays. Since the discovery of this phenomenon in the 1990s, harmonic signals at these very low frequencies have come to be known as the Earth's "hum." A number of hypotheses have been suggested for the Earth's hum, including forcing by atmospheric turbulence, ocean waves, and, most recently, the Sun. We test the solar hypothesis by searching for statistically significant harmonic lines that correlate with independently observed solar free oscillations. The solar model assumes that free oscillations of the sun modulate the solar wind, producing pure harmonic components of Earth's magnetic field that are postulated to couple to the ground by electromagnetic induction. In this thesis we search the multitaper spectrum of stacks of seismic instruments for solar normal frequencies. We use a median stack instead of the more conventional mean because a more robust estimate of center is required for these low signal-to-noise data with occasional transients. A key advantage of a stack is that data gaps are easily ignored when computing the beam. Results from a stack of 18 Transportable Array stations show multiple possible g-mode detections at the 95-99% confidence level. We are presently applying this method to data from the Homestake Mine array, and may also do so with data from a broadband borehole array currently operating at Pinon Flats, California.

  1. Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic Rifting

    NASA Astrophysics Data System (ADS)

    Lambert, C.; Muirhead, J.; Ebinger, C. J.; Tiberi, C.; Roecker, S. W.; Ferdinand-Wambura, R.; Kianji, G.; Mulibo, G. D.

    2014-12-01

    The volcanically active East African rift system in southern Kenya and northern Tanzania transects thick cratonic lithosphere, and comprises several basins characterized by deep crustal seismicity. The US-French-Tanzania-Kenya CRAFTI project aims to understand the role of magma and volatile movement during the initiation and evolution of rifting in cratonic lithosphere. Our 38-station broadband network spans all or parts of fault-bounded rift segments, enabling comparison of lithospheric structure, fault kinematics, and seismogenic layer thickness with age and proximity to the deeply rooted Archaen craton. Seismicity levels are high in all basins, but we find profound differences in seismogenic layer thickness along the length of the rift. Seismicity in the Manyara basin occurs almost exclusively within the lower crust, and in spatial clusters that have been active since 1990. In contrast, seismicity in the ~ 5 My older Magadi basin is localized in the upper crust, and the long border fault bounding the west side of the basin is seismically inactive. Between these two basins lies the Natron rift segment, which shows seismicity between ~ 20 and ~2 km depth, and high concentrations at Oldoinyo Lengai and Gelai volcanoes. Older volcanoes on the uplifted western flank (e.g., Ngorongoro) experience swarms of activity, suggesting that active magmatism and degassing are widespread. Focal mechanisms of the frequent earthquakes recorded across the array are spatially variable, and indicate a stress field strongly influenced by (1) Holocene volcanoes, (2) mechanical interactions between adjacent rift basins, and (3) a far-field ESE-WNW extensional stress regime. We explore the spatial correlation between zones of intense degassing along fault systems and seismicity, and examine the influence of high gas pressures on lower and upper crustal seismicity in this youthful cratonic rift zone.

  2. Real feature of seismicity around Palau trench region, western Pacific: Is Palau trench aseismic silent plate boundary?

    NASA Astrophysics Data System (ADS)

    Ishihara, Y.; Shito, A.; Tanaka, S.; Suetsugu, D.

    2012-12-01

    Palau islands locate around plate converging zone in the western Pacific region. In the east off the Palau islands, obvious trench topography is developed whose bathymetry reaches about 6000 meters. Palau trench locates at the west side of Yap trench. However tectonic activity is quite different in the both trenches. Yap trench has active seismic activity associate with subduction process. Plate motion model shows clear convergent relative motion between Pacific plate and Philippine Sea plate at Yap trench. On the other hand, Palau trench doesn't have active seismicity according to ISC catalogue. In ten years in 2000's, only three small earthquakes are reported in ISC catalogue. Historically any great earthquake also is not reported. Recent plate motion model shows very low convergent motion at Palau trench though developed trench structure. Our group operates broadband seismic station at Palau (station code: PALU) for about 15 years. In our instant monitoring, local earthquakes sometime are recognized. We operated additional stations in Palau islands for six months to detect local earthquake and to locate hypocenters. Our objective of the research is evaluation of real seismicity of Palau region and final major interest is to understand tectonic activity of Palau trench. We install minimum network for hypocenter locating in Koror and Babeldaob islands, Palau that its array dimension is about 20 km. We use broadband seismographs and high resolution data loggers with GPS clock and solar power generators. We succeeded continuous recording without any troubles and clips of mass position. By careful motoring, we pick up greater than 70 local earthquakes in only six months. And we also tried to read the P and S wave arrival times. We succeeded to locate 27 hypocenters. The number of seismic events is much higher than initial estimation. The hypocenters locate east coast side of Palau islands where is trench side. The overview of distribution is parallel to trench

  3. Analysis of Brazilian data for seismic hazard analysis

    NASA Astrophysics Data System (ADS)

    Drouet, S.; Assumpção, M.

    2013-05-01

    Seismic hazard analysis in Brazil is going to be re-assessed in the framework of the Global Earthquake Model (GEM) project. Since the last worldwide Global Seismic Hazard Analysis Project (GSHAP) there has been no specific study in this field in Brazil. Brazil is a stable continental region and is characterized by a low seismic activity. In this particular type of regions, seismic hazard assessment is a very hard task due to the limited amount of data available regarding the seismic sources, earthquake catalogue, or ground-motion amplitudes, and the uncertainties associated are very large. This study focuses on recorded data in South-East Brazil where broadband stations are installed, belonging to two networks: the network managed by the seismology group at the IAG-USP in São Paulo which exists since about 20 years, and the network managed by the Observatorio Nacional in Rio de Janeiro which has just been set up. The two networks are now integrated into the national network RSB (Rede Sismográfica Brasileira) which will also include stations from the rest of Brazil currently in installation by the Universities of Brasilia and Natal. There are a couple of events with magnitude greater than 3 recorded at these very sensitive stations, usually at rather large distances. At first sight these data may appear meaningless in the context of seismic hazard but they can help to improve different parts involved in the process. The analysis of the S-wave Fourier spectra can help to better resolve source, path and site effects in Brazil. For instance moment magnitudes can be computed from the flat part of the Fourier spectra. These magnitudes are of utmost importance in order to build an homogeneous catalogue in terms of moment magnitude. At the moment only body wave magnitude (or some equivalent scale) are determined routinely for the events in Brazil. Attenuation and site effect, especially the high-frequency attenuation known as the kappa effect will also help to

  4. CRUSTAL TECTONICS AND SEISMICITY OF THE MIDDLE EAST

    NASA Astrophysics Data System (ADS)

    Ghalib, H. A.; Gritto, R.; Sibol, M. S.; Herrmann, R. B.; Aleqabi, G. I.; Caron, P. F.; Wagner, R. A.; Ali, B. S.; Ali, A. A.

    2009-12-01

    The Arabian plate describes a geological entity and a dynamic system that has been in continuous interaction with the African plate to the west and south and the Eurasian plate to the north and east. The western and southern boundaries are distinguished by see floor spreading along the Gulf of Aden and Red Sea and transform faulting along the Dead Sea, whereas the northern and eastern boundaries are portrayed by compressional suture zones under thrusting the Turkish and Iranian plateaus. Despite this favorable juxtaposition of continental land masses and the plethora of national seismic networks in every country of the Middle East, the majority of published research on the Arabian plate and surrounding tectonic blocks still depends primarily on global seismographic stations and occasional local networks. Since 2005, we deployed a number of seismic stations, and more recently a five elements array, in close proximity to the northeastern boundary of the Arabian plate. The primary objective of the effort is to better understand the regional seismicity and seismotectonics of the Arabian plate and surrounding regions. To date over a terabyte of high quality 100 sps continuous three-component broadband data have been collected and being analyzed to derive models representative of the greater Middle East tectonic setting. This goal is, in part, achieved by estimating local and regional seismic velocity models using receiver function and surface wave dispersion analyses, and by using these models to obtain accurate hypocenter locations and event focal mechanisms. The resulting events distribution reveals a distinct picture of the interaction between the seismicity and tectonics of the region. The highest seismicity rate seems to be confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases again in the Bandar Abbas region. Spatial distribution of the events and stations provide thorough

  5. Multiscale Finite-frequency Seismic Imaging of the Southern Alaska Subduction Zone

    NASA Astrophysics Data System (ADS)

    Song, X.; Hung, S. H.; Tong, P.; Liu, Q.

    2015-12-01

    Southern Alaska is one of the most seismically active regions in north America as the Pacific plate subducts northward beneath North America plate along the Aleutian trench. In this study, we determine 3-D variations of P- and S-wave speed and Possion's ratio (Vp/Vs) perturbations of the southern Alaska subduction zone based on broadband tele-seismic data recorded by 198 seismic stations for about 2000 events with magnitudes greater than 5.5 during the period from June 2000 to December 2014. Relative arrival times of P and S phases bwtween stations are accurately measured by adapting the efficient multi-channel cross-correlation (MCCC) technique. The obtained arrival-time data are then used to tomographically image the Vp and Vs structures beneath the stations based on 3-D finite-frequency sensitivity kernels and a wavelet-based multi-scale model parameterization. Our results show strong positive velocity anomalies in the crust and upper mantle starting at a depth of about 50km and extending to northwestward down to a depth of 200 km and covering about 350 km in horizontal distance. The high velocity feature interpreted as a cold slab has a thickness of about 50km and a subducting angle of about 45o, consistent with some previous studies of southern Alaska. We also plan to further obtain high-resolution seismic imaging of southern Alaska subduction zone by utilizing the converted and coda waves of tele-seismic main phases (e.g., P and S) based on a hybrid tomographic technique combining spectral-element method (SEM) and frequency-wavenumber (FK) method. The 3D Vp and Vs models obtained from finite-frequency traveltime tomography thus can serve as a proper starting velocity model for the hybrid SEM-FK imaging to further reveal high-resolution details of the subduction zone.

  6. Variation of seismic source parameters around the southern Korean Peninsula

    NASA Astrophysics Data System (ADS)

    Rhee, H. M.; Sheen, D. H.; Kang, T. S.

    2014-12-01

    In this study, we determined seismic source parameters from 557 events with ML≥1.6 that occurred in the southern part of the Korean Peninsula from 2001 to 2013. A total of 7,267 S-wave trains on three-component seismograms recorded at broadband seismic stations were used for measuring the corner frequency, Brune stress drop and moment magnitude by using the iterative method of Jo and Baag (2001) based on the methods of Snoke (1987) and Andrews (1986). The SNR were calculated for each seismogram to exclude the possible contamination of the records by noise and/or instrumental malfunctioning. For the stable correction of attenuation, we tested several Q factors from the previous studies on those for the Korean Peninsula and found Kim (2007) gave the best result. In this study, as shown by Shi et al. (1998), the stress drop tended to decrease with decreasing seismic moment from the magnitude 3.5. Although there was large scatter in stress drop, however, the stress drops seemed to be constant for the larger events and the average stress drop was estimated to around 45.5 bar. It is interesting that there was a variation in stress drops depending on earthquake location: stress drops of the earthquakes occurred in the East Sea (Japan Sea) and the southwestern part of North Korea were relatively lower than those for the events occurred at other region in the southern Korean Peninsula.

  7. Evaluation of Flexible Array Station Performance and Ambient Noise Analysis Using 500 Days of Continuous Recordings

    NASA Astrophysics Data System (ADS)

    Alvarez, M. G.; Anderson, K.; Arias-Dotson, E.; Fowler, J.; Woodward, R.

    2008-12-01

    Within the NSF funded EarthScope USArray program, the Flexible Array (FA) is a pool of campaign seismic instruments for Principal Investigator-driven studies to augment the Transportable Array footprint in imaging key geophysical targets at higher resolution. In this study we evaluate the performance of FA stations using data recorded from the EarthScope CAFÉ experiment in western Washington. Using this unique data set, we create a reference point on how well portable broadband stations perform for an extended continuous period of over 500 days (150:2006 - 50:2008) . All instrumentation that comprise the CAFE experiment is essentially new, of the same type and deployed using a uniform installation technique. The performance of 60 stations is analyzed; 46 stations are broadband, equipped with Guralp CMG 3T and Reftek R130's, the remainder equipped with short period Guralp CMG 40T1Hz and the same data acquisition system. The information used for this evaluation is derived from three sources; detailed field service notes kindly provided by the PI's (Ken Creager, Stephane Rondenay, Geoff Abers), data reports from the IRIS Data Management Center, and the actual time series data. The data return (based on data archived at the DMC w/o any problems) for this experiment is calculated to be 94.5% . The various failures through time are segregated into logical categories where trends in deployment techniques and equipment failures are quantified. Using McNamara statistical analysis to characterize background seismic noise, probability density functions were computed for 25 CAFE stations spanning over 500 days of recording beginning in mid 2006. Results from each station were then combined to produce a network wide characterization of the background noise level. For the same time period, PSD's for 35 nearby Transportable Array stations were also computed and combined into a single system wide PSD. Both installation types perform remarkable well with some differences being

  8. Seismic Body-Wave Interferometry Using Noise Auto-correlations for Crustal Structure

    NASA Astrophysics Data System (ADS)

    Oren, Can; Nowack, Robert L.

    2016-10-01

    In this study, we use ambient seismic noise recorded at selected broadband USArray Earthscope Transportable Array (TA) stations to obtain effective reflection seismograms using noise auto-correlations. In order to best retrieve the body-wave component of the Green's function beneath a station from ambient seismic noise, a number of processing steps are used, including temporal sign-bit normalization, spectral whitening, and band-pass filtering. Hourly auto-correlations are stacked for different time periods including one day, one month, and one year. On the final stack, different amplitude gain functions are applied, including automatic gain control (AGC), to equalize the correlation amplitudes. The robustness of the resulting ambient noise auto-correlations is first tested on a TA station in Nevada where we are able to identify arrivals similar to those found in an earlier study. We then investigated noise auto-correlations applied to several USArray TA stations in the central U.S., and the results were then compared with reflectivity synthetics for an average crustal model based on CRUST 1.0 where an AGC was used to enhance the later arrivals. Different stacking periods are also investigated in order to find stable correlation stacks.

  9. The AlpArray Seismic Network: current status and next steps

    NASA Astrophysics Data System (ADS)

    Hetényi, György; Molinari, Irene; Clinton, John; Kissling, Edi

    2016-04-01

    The AlpArray initiative (http://www.alparray.ethz.ch) is a large-scale European collaboration to study the entire Alpine orogen at high resolution and in 3D with a large variety of geoscientific methods. The core element of the initiative is an extensive and dense broadband seismological network, the AlpArray Seismic Network (AASN), which complements the permanent seismological stations to ensure homogeneous coverage of the greater Alpine area. The some 260 temporary stations of the AlpArray Seismic Network are operated as a joint effort by a number of institutions from Austria, Bosnia-Herzegovina, Croatia, Czech Republic, France, Germany, Hungary, Italy, Slovakia and Switzerland. The first stations were installed in Spring 2015 and the full AASN is planned to be operational by early Summer 2016. In this poster we present the actual status of the deployment, the effort undertaken by the contributing groups, station performance, typical noise levels, best practices in installation as well as in data management, often encountered challenges, and planned next steps including the deployment of ocean bottom seismometers in the Ligurian Sea.

  10. Development of an event search and download system for analyzing waveform data observed at seafloor seismic network, DONET

    NASA Astrophysics Data System (ADS)

    Takaesu, M.; Horikawa, H.; Sueki, K.; Kamiya, S.; Nakamura, T.; Nakano, M.; Takahashi, N.; Sonoda, A.; Tsuboi, S.

    2014-12-01

    Mega-thrust earthquakes are anticipated to occur in the Nankai Trough in southwest Japan. In the source areas, we installed seafloor seismic network, DONET (Dense Ocean-floor Network System for Earthquake and Tsunamis), in 2010 in order to monitor seismicity, crustal deformations, and tsunamis. DONET system consists of totally 20 stations, which is composed of six kinds of sensors; strong-motion and broadband seismometers, quartz and differential pressure gauges, hydrophone, and thermometer. The stations are densely distributed with an average spatial interval of 15-20 km and cover near coastal areas to the trench axis. Observed data are transferred to a land station through a fiber-optical cable and then to JAMSTEC (Japan Agency for Marine-Earth Science and Technology) data management center through a private network in real time. The data are based on WIN32 format in the private network and finally archived in SEED format in the management center to combine waveform data with related metadata. We are developing a web-based application system to easily download seismic waveform data of DONET. In this system, users can select 20 Hz broadband (BH type) and 200 Hz strong-motion (EH type) data and download them in SEED. Users can also search events from the options of time periods, magnitude, source area and depth in a GUI platform. Event data are produced referring to event catalogues from USGS and JMA (Japan Meteorological Agency). The thresholds of magnitudes for the production are M6 for far-field and M4 for local events using the USGS and JMA lists, respectively. Available data lengths depend on magnitudes and epicentral distances. In this presentation, we briefly introduce DONET stations and then show our developed application system. We open DONET data through the system and want them to be widely recognized so that many users analyze. We also discuss next plans for further developments of the system.

  11. Seismic tomography and dynamics of geothermal and natural hydrothermal systems in the south of Bandung, Indonesia

    NASA Astrophysics Data System (ADS)

    Jousset, Philippe; Sule, Rachmat; Diningrat, Wahyuddin; Syahbana, Devy; Schuck, Nicole; Akbar, Fanini; Kusnadi, Yosep; Hendryana, Andri; Nugraha, Andri; Ryannugroho, Riskiray; Jaya, Makki; Erbas, Kemal; Bruhn, David; Pratomo, Bambang

    2015-04-01

    The structure and the dynamics of geothermal reservoirs and hydrothermal systems allows us to better assess geothermal resources in the south of Bandung. A large variety of intense surface manifestations like geysers, hot-steaming grounds, hot water pools, and active volcanoes suggest an intimate coupling between volcanic, tectonic and hydrothermal processes in this area. We deployed a geophysical network around geothermal areas starting with a network of 30 seismic stations including high-dynamic broadband Güralp and Trillium sensors (0.008 - 100 Hz) and 4 short-period (1 Hz) sensors from October 2012 to December 2013. We extended the network in June 2013 with 16 short-period seismometers. Finally, we deployed a geodetic network including a continuously recording gravity meter, a GPS station and tilt-meters. We describe the set-up of the seismic and geodetic networks and we discuss observations and results. The earthquakes locations were estimated using a non-linear algorithm, and revealed at least 3 seismic clusters. We perform joint inversion of hypo-center and velocity tomography and we look at seismic focal mechanisms. We develop seismic ambient noise tomography. We discuss the resulting seismic pattern within the area and relate the structure to the distribution of hydrothermal systems. We aim at searching possible structural and dynamical links between different hydrothermal systems. In addition, we discuss possible dynamical implications of this complex volcanic systems from temporal variations of inferred parameters. The integration of those results allows us achieving a better understanding of the structures and the dynamics of those geothermal reservoirs. This approach contributes to the sustainable and optimal exploitation of the geothermal resource in Indonesia.

  12. Surface dynamic deformation estimates from local seismicity: the Itoiz reservoir, Spain

    NASA Astrophysics Data System (ADS)

    Santoyo, Miguel A.; Martínez-Garzón, Patricia; García-Jerez, Antonio; Luzón, Francisco

    2016-07-01

    We analyze the ground motion time histories due to the local seismicity near the Itoiz reservoir to estimate the near-source, surface 3D displacement gradients and dynamic deformations. The seismic data were obtained by a semipermanent broadband and accelerometric network located on surface and at underground sites. The dynamic deformation field was calculated by two different methodologies: first, by the seismo-geodetic method using the data from a three-station microarray located close to the dam, and second, by single station estimates of the displacement gradients. The dynamic deformations obtained from both methods were compared and analyzed in the context of the local free-field effects. The shallow 1D velocity structure was estimated from the seismic data by modeling the body wave travel times. Time histories obtained from both methods result quite similar in the time window of body wave arrivals. The strain misfits between methods vary from 1.4 to 35.0 % and rotational misfits vary from 2.5 to 36.0 %. Amplitudes of displacement gradients vary in the range of 10-8 to 10-7 strains. From these results, a new scaling analysis by numerical modeling is proposed in order to estimate the peak dynamic deformations for different magnitudes, up to the expected maximum M w in the region (M5.5). Peak dynamic deformations due to local M w5.5 earthquakes would reach amplitudes of 10-5 strain and 10-3 radians at the Itoiz dam. The single station method shows to be an adequate option for the analysis of local seismicity, where few three-component stations are available. The results obtained here could help to extend the applicability of these methodologies to other sites of engineering interest.

  13. Seismic Energy From Waterfalls in Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Workman, E. J.; Koper, K. D.; Burlacu, R.; Lin, F. C.

    2014-12-01

    We surveyed continuous seismic data recorded at two seismic stations in Yellowstone National Park that are located near to Yellowstone National Park's Upper and Lower Falls. Lower Falls is the largest waterfall in Yellowstone, with an estimated flow rate of 70 cubic meters per second, falling an estimated 94 meters, while the Upper Falls has a flow of 70 cubic meters per second, jetting over a 21 meter gap downward 33 meters. A study based on a deployment of seismometers in Yellowstone in September and October of 1972 had found a predominant 2 Hz signal associated with the Lower Falls, with the signal remaining above background noise within 6 km of the falls in every direction but the south. Station YUF is a three-component, broadband seismometer operated by the University of Utah Seismograph Stations that is located approximately 1.5 km southwest of the Lower Falls, while station B206 is a three-component, short-period, borehole seismometer operated by the Plate Boundary Observatory, located roughly 1.2 km west of the Lower Falls. We computed power spectral densities (PSD) for all available hour-long segments of continuous data from the vertical components of YUF and B206 beginning September 22, 2006 and July 10, 2008, respectively. Yearly spectrograms were used to visualize the PSDs. Both stations showed spectral peaks in the double-frequency microseismic band, with stronger amplitudes in winter than in summer, presumably generated mainly by storms in the North Pacific. Both also showed strong peaks near a period of 1 s, but with the opposite seasonal dependence. This 1 s peak signal broadens in frequency during the summer, from 1 to 5 Hz, as well as uniformly increasing in power across this band. This short-period noise was compared to discharge measurements of the Yellowstone River made at the Yellowstone Lake outlet, about 18.5 km upstream from the Upper Falls. For periods of 0.5-2.0 s the correlation coefficient between the seismic energy and the river

  14. Extracting source characteristics and dynamics of the August 2010 Mount Meager landslide from broadband seismograms

    NASA Astrophysics Data System (ADS)

    Allstadt, Kate

    2013-09-01

    methods can substantially improve the characterization of the dynamics of large and rapid landslides. Such landslides often generate strong long-period seismic waves due to the large-scale acceleration of the entire landslide mass, which, according to theory, can be approximated as a single-force mechanism at long wavelengths. I apply this theory and invert the long-period seismic waves generated by the 48.5 Mm3 August 2010 Mount Meager rockslide-debris flow in British Columbia. Using data from five broadband seismic stations 70 to 276 km from the source, I obtain a time series of forces the landslide exerted on the Earth, with peak forces of 1.0 × 1011 N. The direction and amplitude of the forces can be used to determine the timing and occurrence of events and subevents. Using this result, in combination with other field and geospatial evidence, I calculate an average horizontal acceleration of the rockslide of 0.39 m/s2 and an average apparent coefficient of basal friction of 0.38 ± 0.02, which suggests elevated basal fluid pressures. The direction and timing of the strongest forces are consistent with the centripetal acceleration of the debris flow around corners in its path. I use this correlation to estimate speeds, which peak at 92 m/s. This study demonstrates that the time series recording of forces exerted by a large and rapid landslide derived remotely from seismic records can be used to tie post-slide evidence to what actually occurred during the event and can serve to validate numerical models and theoretical methods.

  15. Comprehensive Analysis of Broadband Data of Densely Distributed Broadband CNDSN for Crustal and Upper Mantle Structure in China

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Niu, F.; Huang, Z.; Liu, R.

    2013-12-01

    The new Chinese National Digital Seismic Network (CNDSN) consists of 144 national backbone stations and hundreds of regional stations deployed in all provinces. The large amount of high-quality broadband seismic waveform data recorded at these stations allowed us to conduct comprehensive studies of the crustal and upper mantle structure of China. This study mainly focused on the analysis of teleseismic receiver function and Rayleigh wave dispersion data. Specifically: (1) We estimated the crustal thickness and Vp/Vs ratio (hence Poisson's ratio) with an advanced H-κ analysis of receiver function data on each station. (2) We next inverted these receiver function data for a 1D S-wave velocity profile with depth. In order to stabilize the linearized inversion, we developed a ray-parameter based stacking method to correct the move-outs in converted and reverberated phase arrivals and normalize the amplitude for the preparation of stacked data and employed multiple pre-conditions on the inversion procedure. Moreover, we well constructed starting model with mulit-constraints from independent studies. (3) We developed high-resolution Rayleigh wave group velocity tomographic models at periods range from 10s to 80s. (4) With the Rayleigh wave dispersions extracted from the group velocity tomography at each station, the joint inversion of receiver function and surface wave data released the limits when using individual data set. Taking the advantage of dense distribution of the stations in CNDSN, we were able to extend the 1D models of all stations to a 3D model and review their lateral variations across China. The mainland of China is believed highly diversely in geology, consisting of various tectonic blocks from ancient Archean cratons to young and active orogens. Our crustal thinness model indicates that the crust varies from 29km to 37km to the eastern part of China, and gradually increase to 45 ~ 50km towards the central and northwestern parts. The Tibetan plateau

  16. Crustal Structure of the Middle East from Regional Seismic Studies

    NASA Astrophysics Data System (ADS)

    Gritto, Roland; Sibol, Matthew; Caron, Pierre; Ghalib, Hafidh; Chen, Youlin

    2010-05-01

    We present results of crustal studies obtained with seismic data from the Northern Iraq Seismic Network (NISN). NISN has operated ten broadband stations in north-eastern Iraq since late 2005. This network was supplemented by the five-element broadband Iraq Seismic Array (KSIRS) in 2007. More recently, the former Iraq Seismic Network (ISN), destroyed during the war with Iran, was reestablished with the deployment of six broadband stations throughout Iraq. The aim of the present study is to derive models of the local and regional crustal structure of the Middle East, including Eastern Turkey, Iraq and Iran. To achieve this goal, we derive crustal velocity models using receiver function, surface wave and body wave analyses. These refined velocity models will eventually be used to obtain accurate hypocenter locations and event focal mechanisms. Our analysis of preliminary hypocenter locations produced a clearer picture of the seismicity associated with the tectonics of the region. The largest seismicity rate is confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases in the Bandar Abbas region again. Additionally, the rift zones in the Red Sea and the Gulf of Aden are clearly demarked by high seismicity rates. Surface wave velocity analysis resulted in a clear demarcation of the tectonic features in the region. The Arabian shield, Zagros thrust zone and the Red Sea are apparent through distinct velocity distributions separating them from each other. Furthermore, the shear wave velocity of the crust in North Iraq appears to be 10% higher than that of the Iranian plateau. The velocity anomaly of the Zagros mountains appears to be present into the upper mantle beyond the resolving limit of our model. Analysis of waveform data for obstructed pathways indicates clear propagation paths from the west or south-west across the Arabian shield as well as from the north and east into NISN. Phases

  17. Estimating correlations of neighbouring frequencies in ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Ben-Zion, Yehuda

    2016-08-01

    Extracting accurate empirical Green's functions from the ambient seismic noise field requires the noise to be fully diffuse and that different frequency components are not correlated. Calculating a matrix of correlation coefficients of power spectral samples can be used to estimate deviations from a fully diffuse random noise field in the analysed frequency range. A fully diffuse field has correlations only in a narrow region around the diagonal of the matrix, with frequency resolution inversely proportional to length of the used time window. Analysis of low-frequency data (0.005-0.6 Hz) recorded by three broad-band stations of the southern California seismic network reveals three common types of correlations, manifested in the correlation coefficient matrix as square, diagonal halo and correlated stripes. Synthetic calculations show that these types of signatures in the correlation coefficient matrix can result from certain combinations of cross-frequency correlated random components and diffuse field. The analysis of observed data indicates that the secondary microseismic peak around 0.15 Hz is correlated with its neighbouring frequencies, while the primary peak around 0.06 Hz is more diffuse. This suggests that the primary and secondary peaks may be associated with somewhat different physical origins. In addition, significant correlation of frequencies below that of the primary microseismic peak suggests that the very low frequencies noise is less scattered during propagation. The power spectra recorded by a station close to the edge of the Los Angeles basin is higher compared to data recorded by stations outside the basin perhaps because of enhanced basin reverberations and/or closer proximity to the ocean. This and other regional variations should be tested further using data from many more stations.

  18. Seismic databases and earthquake catalogue of the Caucasus

    NASA Astrophysics Data System (ADS)

    Godoladze, Tea; Javakhishvili, Zurab; Tvaradze, Nino; Tumanova, Nino; Jorjiashvili, Nato; Gok, Rengen

    2016-04-01

    The Caucasus has a documented historical catalog stretching back to the beginning of the Christian era. Most of the largest historical earthquakes prior to the 19th century are assumed to have occurred on active faults of the Greater Caucasus. Important earthquakes include the Samtskhe earthquake of 1283, Ms~7.0, Io=9; Lechkhumi-Svaneti earthquake of 1350, Ms~7.0, Io=9; and the Alaverdi(earthquake of 1742, Ms~6.8, Io=9. Two significant historical earthquakes that may have occurred within the Javakheti plateau in the Lesser Caucasus are the Tmogvi earthquake of 1088, Ms~6.5, Io=9 and the Akhalkalaki earthquake of 1899, Ms~6.3, Io =8-9. Large earthquakes that occurred in the Caucasus within the period of instrumental observation are: Gori 1920; Tabatskuri 1940; Chkhalta 1963; 1991 Ms=7.0 Racha earthquake, the largest event ever recorded in the region; the 1992 M=6.5 Barisakho earthquake; Ms=6.9 Spitak, Armenia earthquake (100 km south of Tbilisi), which killed over 50,000 people in Armenia. Recently, permanent broadband stations have been deployed across the region as part of various national networks (Georgia (~25 stations), Azerbaijan (~35 stations), Armenia (~14 stations)). The data from the last 10 years of observation provides an opportunity to perform modern, fundamental scientific investigations. A catalog of all instrumentally recorded earthquakes has been compiled by the IES (Institute of Earth Sciences, Ilia State University). The catalog consists of more then 80,000 events. Together with our colleagues from Armenia, Azerbaijan and Turkey the database for the Caucasus seismic events was compiled. We tried to improve locations of the events and calculate Moment magnitudes for the events more than magnitude 4 estimate in order to obtain unified magnitude catalogue of the region. The results will serve as the input for the Seismic hazard assessment for the region.

  19. Functional performance requirements for seismic network upgrade

    SciTech Connect

    Lee, R.C.

    1991-08-18

    The SRL seismic network, established in 1976, was developed to monitor site and regional seismic activity that may have any potential to impact the safety or reduce containment capability of existing and planned structures and systems at the SRS, report seismic activity that may be relevant to emergency preparedness, including rapid assessments of earthquake location and magnitude, and estimates of potential on-site and off-site damage to facilities and lifelines for mitigation measures. All of these tasks require SRL seismologists to provide rapid analysis of large amounts of seismic data. The current seismic network upgrade, the subject of this Functional Performance Requirements Document, is necessary to improve system reliability and resolution. The upgrade provides equipment for the analysis of the network seismic data and replacement of old out-dated equipment. The digital network upgrade is configured for field station and laboratory digital processing systems. The upgrade consists of the purchase and installation of seismic sensors,, data telemetry digital upgrades, a dedicated Seismic Data Processing (SDP) system (already in procurement stage), and a Seismic Signal Analysis (SSA) system. The field stations and telephone telemetry upgrades include equipment necessary for three remote station upgrades including seismic amplifiers, voltage controlled oscillators, pulse calibrators, weather protection (including lightning protection) systems, seismometers, seismic amplifiers, and miscellaneous other parts. The central receiving and recording station upgrades will include discriminators, helicopter amplifier, omega timing system, strong motion instruments, wide-band velocity sensors, and other miscellaneous equipment.

  20. Seismicity of the Jalisco Block

    NASA Astrophysics Data System (ADS)

    Nunez-Cornu, F. J.; Rutz, M.; Camarena-Garcia, M.; Trejo-Gomez, E.; Reyes-Davila, G.; Suarez-Plascencia, C.

    2002-12-01

    In April 2002 began to transmit the stations of the first phase of Jalisco Telemetric Network located at the northwest of Jalisco Block and at the area of Volcan de Fuego (Colima Volcano), in June were deployed four additional MarsLite portable stations in the Bahia de Banderas area, and by the end of August one more portable station at Ceboruco Volcano. The data of these stations jointly with the data from RESCO (Colima Telemetric Network) give us the minimum seismic stations coverage to initiate in a systematic and permanent way the study of the seismicity in this very complex tectonic region. A preliminary analysis of seismicity based on the events registered by the networks using a shutter algorithm, confirms several important features proposed by microseismicity studies carried out between 1996 and 1998. A high level of seismicity inside and below of Rivera plate is observed, this fact suggest a very complex stress pattern acting on this plate. Shallow seismicity at south and east of Bahia de Banderas also suggest a complex stress pattern in this region of the Jalisco Block, events at more than 30 km depth are located under the mouth of the bay and in face of it, a feature denominated Banderas Boundary mark the change of the seismic regime at north of this latitude (20.75°N), however some shallow events were located at the region of Nayarit.

  1. The 2007 Sumatra seismic sequence revealed by a regional seismic network in Indonesia

    NASA Astrophysics Data System (ADS)

    Nakano, M.; Inoue, H.; Kumagai, H.; Yamashina, T.; Sunarjo; Fauzi; Suhardjono

    2007-12-01

    distributed in a region extending about 300 km along the subduction zone of the Indo-Australian Plate. The depths of aftershocks range from 15 to 60 km. In the off-Bengkulu region, the earthquakes with M8 or above occurred in 1381, 1608 and 1833, approximately every 230 years. Now 174 years have been passed since the last event in 1833. We did not experience M8 class earthquakes during the last 210 years in the off-Padang region, which is to the north of off-Bengkulu. The off-Padang region corresponds to a seismic gap between the source regions of the 2007 Sumatra seismic sequence and M8.7 Nias earthquake on March 2005. The sequence of the M8.4, M8.0, and M6.8 earthquakes moving towards the northwest from off-Bengkulu in the 2007 seismic activity suggests the imminency of a large earthquake off Padang. We have been deploying broadband seismograph networks in Indonesia, including JISNET, by an international cooperation among Indonesia, Germany, China, and Japan, aiming at improving the capabilities to monitor seismic activity and tsunami generation in Indonesia. The seismic networks are now in operation, and totally 150 seismic stations will be installed by the end of 2008. Seismic monitoring based on these regional networks would contribute to early notification of a large earthquake anticipated to occur in the off-Padang region.

  2. Geologic interpretations of seismic data: Braintree-Weymouth by-pass stations 29-56, Liberty Street grade separation in Braintree, Massachusetts

    USGS Publications Warehouse

    May, James E.; Linehan, Rev. Daniel

    1950-01-01

    At the request of the Massachusetts Department of Public Works, seismic and geologic studies were made for the projected Braintree-Weymouth By-Pass grade separation at Liberty Street in Braintree, Massachusetts. The work was performed in order to furnish data that would aid the engineers in preparing estimates of the quantity of bedrock to be excavated for this project. The study represents part of a cooperative program of the Massachusetts Department of Public Works and the United States Geological Survey. The work was performed in May 1949.

  3. Discrimination of DPRK M5.1 February 12th, 2013 Earthquake as Nuclear Test Using Analysis of Magnitude, Rupture Duration and Ratio of Seismic Energy and Moment

    NASA Astrophysics Data System (ADS)

    Salomo Sianipar, Dimas; Subakti, Hendri; Pribadi, Sugeng

    2015-04-01

    On February 12th, 2013 morning at 02:57 UTC, there had been an earthquake with its epicenter in the region of North Korea precisely around Sungjibaegam Mountains. Monitoring stations of the Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) and some other seismic network detected this shallow seismic event. Analyzing seismograms recorded after this event can discriminate between a natural earthquake or an explosion. Zhao et. al. (2014) have been successfully discriminate this seismic event of North Korea nuclear test 2013 from ordinary earthquakes based on network P/S spectral ratios using broadband regional seismic data recorded in China, South Korea and Japan. The P/S-type spectral ratios were powerful discriminants to separate explosions from earthquake (Zhao et. al., 2014). Pribadi et. al. (2014) have characterized 27 earthquake-generated tsunamis (tsunamigenic earthquake or tsunami earthquake) from 1991 to 2012 in Indonesia using W-phase inversion analysis, the ratio between the seismic energy (E) and the seismic moment (Mo), the moment magnitude (Mw), the rupture duration (To) and the distance of the hypocenter to the trench. Some of this method was also used by us to characterize the nuclear test earthquake. We discriminate this DPRK M5.1 February 12th, 2013 earthquake from a natural earthquake using analysis magnitude mb, ms and mw, ratio of seismic energy and moment and rupture duration. We used the waveform data of the seismicity on the scope region in radius 5 degrees from the DPRK M5.1 February 12th, 2013 epicenter 41.29, 129.07 (Zhang and Wen, 2013) from 2006 to 2014 with magnitude M ≥ 4.0. We conclude that this earthquake was a shallow seismic event with explosion characteristics and can be discriminate from a natural or tectonic earthquake. Keywords: North Korean nuclear test, magnitude mb, ms, mw, ratio between seismic energy and moment, ruptures duration

  4. Structure of Suasselkä Postglacial Fault in northern Finland obtained by analysis of ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Afonin, Nikita; Kozlovskaya, Elena

    2016-04-01

    Understanding inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of ambient seismic noise recorded by the temporary DAFNE array in northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä post-glacial fault (SPGF) that was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised the area of about 20 to 100 km and consisted of 8 short-period and 4 broad-band 3-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September, 2011-May, 2013. Recordings of the array have being analyzed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä Gold Mine. As a result, we found several dozens of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate correspondent surface wave dispersion curves. After that S-wave velocity models were obtained as a result of dispersion curves inversion using Geopsy software. The results suggest that the area of

  5. Development of Alaska Volcano Observatory Seismic Networks, 1988-2008

    NASA Astrophysics Data System (ADS)

    Tytgat, G.; Paskievitch, J. F.; McNutt, S. R.; Power, J. A.

    2008-12-01

    The number and quality of seismic stations and networks on Alaskan volcanoes have increased dramatically in the 20 years from 1988 to 2008. Starting with 28 stations on six volcanoes in 1988, the Alaska Volcano Observatory (AVO) now operates 194 stations in networks on 33 volcanoes spanning the 2000 km Aleutian Arc. All data are telemetered in real time to laboratory facilities in Fairbanks and Anchorage and recorded on digital acquisition systems. Data are used for both monitoring and research. The basic and standard network designs are driven by practical considerations including geography and terrain, access to commercial telecommunications services, and environmental vulnerability. Typical networks consist of 6 to 8 analog stations, whose data can be telemetered to fit on a single analog telephone circuit terminated ultimately in either Fairbanks or Anchorage. Towns provide access to commercial telecommunications and signals are often consolidated for telemetry by remote computer systems. Most AVO stations consist of custom made fiberglass huts that house the batteries, electronics, and antennae. Solar panels are bolted to the south facing side of the huts and the seismometers are buried nearby. The huts are rugged and have allowed for good station survivability and performance reliability. However, damage has occurred from wind, wind-blown pumice, volcanic ejecta, lightning, icing, and bears. Power is provided by multiple isolated banks of storage batteries charged by solar panels. Primary cells are used to provide backup power should the rechargable system fail or fall short of meeting the requirement. In the worst cases, snow loading blocks the solar panels for 7 months, so sufficient power storage must provide power for at least this long. Although primarily seismic stations, the huts and overall design allow additional instruments to be added, such as infrasound sensors, webcams, electric field meters, etc. Yearly maintenance visits are desirable, but some

  6. EMERALD: A Flexible Framework for Managing Seismic Data

    NASA Astrophysics Data System (ADS)

    West, J. D.; Fouch, M. J.; Arrowsmith, R.

    2010-12-01

    The seismological community is challenged by the vast quantity of new broadband seismic data provided by large-scale seismic arrays such as EarthScope’s USArray. While this bonanza of new data enables transformative scientific studies of the Earth’s interior, it also illuminates limitations in the methods used to prepare and preprocess those data. At a recent seismic data processing focus group workshop, many participants expressed the need for better systems to minimize the time and tedium spent on data preparation in order to increase the efficiency of scientific research. Another challenge related to data from all large-scale transportable seismic experiments is that there currently exists no system for discovering and tracking changes in station metadata. This critical information, such as station location, sensor orientation, instrument response, and clock timing data, may change over the life of an experiment and/or be subject to post-experiment correction. Yet nearly all researchers utilize metadata acquired with the downloaded data, even though subsequent metadata updates might alter or invalidate results produced with older metadata. A third long-standing issue for the seismic community is the lack of easily exchangeable seismic processing codes. This problem stems directly from the storage of seismic data as individual time series files, and the history of each researcher developing his or her preferred data file naming convention and directory organization. Because most processing codes rely on the underlying data organization structure, such codes are not easily exchanged between investigators. To address these issues, we are developing EMERALD (Explore, Manage, Edit, Reduce, & Analyze Large Datasets). The goal of the EMERALD project is to provide seismic researchers with a unified, user-friendly, extensible system for managing seismic event data, thereby increasing the efficiency of scientific enquiry. EMERALD stores seismic data and metadata in a

  7. Long term observation in the Nankai Trough region using broadband ocean bottom seismometers and pressure gauges

    NASA Astrophysics Data System (ADS)

    Nakahigashi, K.; Machida, Y.; Isse, T.; Yamada, T.; Mochizuki, K.; Shinohara, M.; Shiobara, H.; Kanazawa, T.; Uehira, K.

    2011-12-01

    Recently, low-frequency earthquakes and slow slip events are recognized in deep region of the plate boundary between the landward plate and the subducting Philippine plate below the southwestern Japan [e.g., Obara, 2002; Kawasaki, 2004]. The very low frequency earthquakes (VLFEs) occurring close to the Nankai Trough are also reported by using the broadband seismograph data obtained in the land area [e.g., Obara and Ito, 2005]. Such unusual seismic events might reflect coupling properties at the plate boundary. It is important to understand such events for consideration of the subduction process and estimation of generation mechanism of the interplate earthquake in the Nankai Trough. Because the VLFEs in the Nankai Trough region occurred far from land seismic stations, observations using broadband Ocean Bottom Seismometers (BBOBSs) near the trough are needed to understand such VLFE activities. In December 2008, we started an observation campaign off Kii Peninsula. For the first observation, three BBOBSs with Guralp CMG-3T sensors, and six 1Hz type Long-term OBSs were used. The spatial intervals among OBSs were about 20km. In 2009, we recovered them. The data recorded by each OBS were merged and continuous records were reproduced. VLFEs with predominant frequency of 0.01-0.1 Hz were found from continuous records in March 2009. The occurrence of the VLFE has a temporal change. In addition, seismicity of ordinary micro-earthquakes became high simultaneously during the VLFE activities. In November 2009, we started the second observation off Cape Muroto, the westward of the first observation, using three BBOBSs with pressure gauge, and five Long-term OBSs. The subducting seamount was found by an OBS survey in this region [Kodaira et al., 2000]. In February 2011, all the OBS were retrieved. We obtained consecutive data of seismometer and pressure gauge. We can identify a tunami signal from 2010 Chile Earthquake (Mw8.8).In February 2001, we deployed five BBOBSs in the same

  8. Infrasound and Seismic Recordings of a US Airstrike on an ISIS Car Bomb Factory on June 3, 2015

    NASA Astrophysics Data System (ADS)

    Aleqabi, G. I.; Ghalib, H. A. A.; Wysession, M. E.

    2015-12-01

    Concurrent infrasound and seismic records of a jet airstrike in Iraq are presented. Media reports stated that US jets carried out a large airstrike on June 3, 2015, just after midnight local time, that targeted and destroyed an ISIS car bomb factory in Hawija, Iraq, just south of the city of Kirkuk, Iraq. The resulting explosion was felt within Kirkuk and at other locations as far as 34 km away from the Hawija factory. Seismic broadband stations located in northern Iraq, at a distance of about 160 km, show clear simultaneous signals of infrasound waves on the seismometers as well as on collocated infrasound equipment. From an analysis of the body waves, the Pg to Lg time difference is nearly ~20 sec, with a back azimuth of 250o to 260o, which is consistent with explosion location. The time difference between the Pg and infrasound signals is just over 7 minutes, consistent with sound speed in the atmosphere. No clear Rg wave was observed. As was demonstrated by Aleqabi, Wysession, and Ghalib [2015, BSSA, in press], broadband seismic recordings are able to identify and distinguish between several different kinds of MOUT (military operations in urban terrain) and even determine the magnitudes of ordinance used in certain blasts. The addition of collocated infrasound equipment provides additional constraints that can be used in the analysis of the size and form of the MOUT.

  9. Planning the improvement of seismic monitoring in a volcanic supersite: experience on Mt. Etna

    NASA Astrophysics Data System (ADS)

    D'Alessandro, Antonino; Scarfi, Luciano; Scaltrito, Antonio; Aiesi, Giampiero; Di Prima, Sergio; Ferrari, Ferruccio; Rapisarda, Salvatore

    2013-04-01

    Etna is one of the most active volcanoes in the world and one of the most intriguing natural laboratories for the understanding of eruptive processes and lava uprising in basalt-type volcanic environments; indeed, it is considered, by the scientific international community, together with the Vesuvius and the Hawaiian Islands, as a volcanic supersite. Its activity is continuously monitored by the Osservatorio Etneo of the Istituto Nazionale di Geofisica e Vulcanologia (INGV), by means of an array of integrated multidisciplinary techniques. In particular, Etna seismicity is recorded by a dense local seismic network (ESN- Etna Seismic Network), which, nowadays, consists of about 40 real-time seismic stations, many of which equipped with broadband velocity and accelerometer sensors. The data are analyzed routinely in detail by the Osservatorio Etneo staff, producing daily and periodic reports and bulletins of the earthquakes located in the whole Sicily and southern Calabria region. In the last decades, seismological observations provided important information on both the dynamics and internal structure of the volcano, in addition to their interaction with the regional tectonic structures. In the last year, in the framework of the VULCAMED project, an INGV workgroup has taken on the task of developing the existing seismic network through the installation of new measurement stations. By considering the spatial distribution of earthquakes in the area, the presence of structures known as seismically active and through extensive geological-geophysical surveys, ten potential new sites were identified. In the following months, some of these sites will complement the existing network. The choice of optimal sites must clearly be made through a careful analysis of environmental noise, of the possible logistics, technical and broadcast problems, but must also take into account the geometry of the existing seismic network. For this purpose, we applied the Seismic Network

  10. The Irpinia Seismic Network (ISN): a new Monitoring Infrastructure for Seismic Alert Management in Campania Region, Southern Italy

    NASA Astrophysics Data System (ADS)

    Iannaccone, G.; Satriano, C.; Weber, E.; Cantore, L.; Corciulo, M.; Romano, L.; Martino, C.; Dicrosta, M.; Zollo, A.

    2005-12-01

    The Irpinia Seismic Network is an high dynamics, high density seismographic network under development in the Southern Apenninic chain. It is deployed in the area stroken by several destructive earthquakes during last centuries. In its final configuration the network will consist of more than fourty high dynamic seismic stations subdivided in physical subnetworks inter-connected by a robust data transmission system. The system is being designed with two primary targets: -Monitoring and analysis of background seismic activity produced by the active fault system which is the cause for large earthquakes in the past, included the 1980, Irpinia earthquake (Ms=6.9) - Development and experimentation of a prototype system for seismic early and post-event warning to be used for protecting public infrastructures and buildings of strategic relevance of the Regione Campania The seismic network will be completed in two stages: 1 - Deployment of 30 seismic stations along the Campania-Lucania Apenninic chain (to date almost completed) 2 - Setting up radio communication system for data transmission. Installation of 12 additional seismic stations (end of year 2006) To ensure an high dynamic recording range each site is equipped with two type of sensors: 30 force-balance accelerometer (model Guralp CMG5-T) and a velocimeter. In particular, 25 sites with short period three components instrument (model Geotech S13-J) and 5 with broad-band sensor (Nanometrics Trillium, with frequency response in the 0.033-50 Hz band). The used data logger is the Osiris-6 model produced by Agecodagis whose main features are: six channels, O/N 24 bit A/D converter, ARM processor with embedded Linux and open source software, two PCMCIA slots (used for two 5GB microdrive or one disk and wi-fi card), Ethernet, wi-fi and serial communication, low power cosumption (~1 W). Power is ensured by two 120 W solar panels and two 130 Ah gel batteries. Each recording site is equipped with a control/alarm system through

  11. Local magnitude calibration of the Hellenic Unified Seismic Network

    NASA Astrophysics Data System (ADS)

    Scordilis, E. M.; Kementzetzidou, D.; Papazachos, B. C.

    2016-01-01

    A new relation is proposed for accurate determination of local magnitudes in Greece. This relation is based on a large number of synthetic Wood-Anderson (SWA) seismograms corresponding to 782 regional shallow earthquakes which occurred during the period 2007-2013 and recorded by 98 digital broad-band stations. These stations are installed and operated by the following: (a) the National Observatory of Athens (HL), (b) the Department of Geophysics of the Aristotle University of Thessaloniki (HT), (c) the Seismological Laboratory of the University of Athens (HA), and (d) the Seismological Laboratory of the Patras University (HP). The seismological networks of the above institutions constitute the recently (2004) established Hellenic Unified Seismic Network (HUSN). These records are used to calculate a refined geometrical spreading factor and an anelastic attenuation coefficient, representative for Greece and surrounding areas, proper for accurate calculation of local magnitudes in this region. Individual station corrections depending on the crustal structure variations in their vicinity and possible inconsistencies in instruments responses are also considered in order to further ameliorate magnitude estimation accuracy. Comparison of such calculated local magnitudes with corresponding original moment magnitudes, based on an independent dataset, revealed that these magnitude scales are equivalent for a wide range of values.

  12. Dual broadband metamaterial absorber.

    PubMed

    Kim, Young Ju; Yoo, Young Joon; Kim, Ki Won; Rhee, Joo Yull; Kim, Yong Hwan; Lee, YoungPak

    2015-02-23

    We propose polarization-independent and dual-broadband metamaterial absorbers at microwave frequencies. This is a periodic meta-atom array consisting of metal-dielectric-multilayer truncated cones. We demonstrate not only one broadband absorption from the fundamental magnetic resonances but additional broadband absorption in high-frequency range using the third-harmonic resonance, by both simulation and experiment. In simulation, the absorption was over 90% in 3.93-6.05 GHz, and 11.64-14.55 GHz. The corresponding experimental absorption bands over 90% were 3.88-6.08 GHz, 9.95-10.46 GHz and 11.86-13.84 GHz, respectively. The origin of absorption bands was elucidated. Furthermore, it is independent of polarization angle owing to the multilayered circular structures. The design is scalable to smaller size for the infrared and the visible ranges.

  13. Passive broadband acoustic thermometry

    NASA Astrophysics Data System (ADS)

    Anosov, A. A.; Belyaev, R. V.; Klin'shov, V. V.; Mansfel'd, A. D.; Subochev, P. V.

    2016-04-01

    The 1D internal (core) temperature profiles for the model object (plasticine) and the human hand are reconstructed using the passive acoustothermometric broadband probing data. Thermal acoustic radiation is detected by a broadband (0.8-3.5 MHz) acoustic radiometer. The temperature distribution is reconstructed using a priori information corresponding to the experimental conditions. The temperature distribution for the heated model object is assumed to be monotonic. For the hand, we assume that the temperature distribution satisfies the heat-conduction equation taking into account the blood flow. The average error of reconstruction determined for plasticine from the results of independent temperature measurements is 0.6 K for a measuring time of 25 s. The reconstructed value of the core temperature of the hand (36°C) generally corresponds to physiological data. The obtained results make it possible to use passive broadband acoustic probing for measuring the core temperatures in medical procedures associated with heating of human organism tissues.

  14. Comparison of the bedrock depth from array measurements of Rayleigh waves associated with microtremor and seismic profile obtained the Seismic Reflection Data, Eskisehir Basin, Turkey

    NASA Astrophysics Data System (ADS)

    Tün, Muammer; Karabulut, Savaş; Özel, Oğuz

    2015-04-01

    Ground motion estimation for future earthquakes is one of the most challenging problems in seismology and earthquake engineering. The bedrock depth has a considerable seismic risk for the urban area of Eskişehir. In this study, multiple station microtremor measurement methods which are more practical, non-distructive, fast and economical compared to seismic reflection method were implemented. These method using microtremor recordings have become a very useful data for microzonation studies because of their simple acquisition and analysis. Extensive ambient noise measurements were performed in the basin of Eskisehir from June 2010 to spring 2012. We use data recorded by a broadband seismometer and digitizer CMG-6TD, Guralp seismometer. Some of the measurement locations, the CMG-6TD sensor was located into 30 cm-deep holes in the ground to avoid strongly wind-generated, long-period noise. Dominant frequency (f), bed-rock depth (h) and shear-wave velocity (Vs) were determined from Spatial Autocorrelation (SPAC) methods. With the SPAC Method, it is possible to constrain the velocity structure underlying the site using microtremor array measurements. The results obtained were compared to the 96-channel seismic reflection data with explosive energy source. Several seismic reflection surveys with P-Gun seismic source have been performed on the same place with array measurements. We used two types of seismic sources: 36 cartridge Gun. Shot interval was 10 meters, group interval (one geophone per group, 48 geophones in total) was 10 meters, near offset was 10 meters, far offset was 480 meters, CDP interval was 5 meters. We adapted the 'Off-End Spread' technique while using the Gun. Reflection images within the sedimentary section correlate well with the velocity structure obtained from SPAC.

  15. Seismic array constraints on the D″ discontinuity beneath Central America

    NASA Astrophysics Data System (ADS)

    Whittaker, Stefanie; Thorne, Michael S.; Schmerr, Nicholas C.; Miyagi, Lowell

    2016-01-01

    We analyzed 16,150 transverse component seismic recordings from 54 deep-focus earthquakes in the South American and Caribbean regions recorded at broadband stations in North America between 2005 and 2012. We treated subgroups of seismic stations within 3° radius geographical bins as seismic arrays and performed vespagram analysis. We focused on the S, ScS, and Scd arrivals and collected data in the epicentral distance range from 55° to 90°. In particular, we searched for D″ discontinuity presence in the vespagrams in a 25° by 35° (or 1520 by 2130 km) area beneath Central America. Analysis of these data showed 125 clear Scd observations, 180 Scd observations of lesser quality, and 343 nonobservations. We produced a new map of the discontinuity height beneath Central America. Our map shows an average discontinuity height of 286 ± 6 km (σ = 76 km). The region is punctuated by a large topographic high centered at approximately 10°N and 90°W with a maximum height of 380 km. Two smaller topographic highs are located at approximately 4°N and 81°W (discontinuity height of 320 km) and at 4°N and 70°W (height of 315 km). The observation of multiple Scd arrivals collocated with the strongest gradients in inferred topography provides evidence for topographic variation on the discontinuity rather than multiple discontinuities. The regions where the discontinuity has the greatest height can be explained by localized enrichment of mid-ocean ridge basalt from the subducted Farallon slab impinging on the core-mantle boundary.

  16. Preliminary Ambient Noise and Seismic Interferometry Analysis of the Laguna del Maule Volcanic Field, Chile

    NASA Astrophysics Data System (ADS)

    Wespestad, C.; Thurber, C. H.; Bennington, N. L.; Zeng, X.; Cardona, C.; Keranen, K. M.; Singer, B. S.

    2015-12-01

    Laguna del Maule Volcanic Field is a large, restless, youthful rhyolitic system in the Southern Andes of Chile. We present a preliminary examination of ambient noise data at this site from 12 University of Wisconsin and 6 OVDAS (Southern Andean Volcano Observatory) broadband seismometers for a 3 month period. Ambient noise tomography seeks to correlate pairs of stations, with one station acting as a virtual source and the other a receiver, generating empirical Green's functions between each pair. The noise correlation functions (NCFs) were computed for day-long and hour-long windows, then the final NCFs were obtained from stacking each time window set. The hour-long NCFs converged more rapidly, so this time window was chosen for use in later stages. This study used phase weighted stacking of the NCFs instead of linear stacking in order to achieve a better signal to noise ratio (SNR), although linearly stacked Green's functions were also created to confirm the improvement. Phase weighted stacking can detect signals with weak amplitudes much more clearly than linear stacking by finding coherence of signals in multiple frequency bins and down-weighting the importance of amplitude for correlation (Schimmel and Gallart, 2007). The Frequency-Time Analysis Technique was utilized to measure group velocity, and initial results show it to be about 2 km/s on average. Fluctuations of the average velocity between different station pairs across this dense array will provide a preliminary indication of the location and size of the magma system. This study also applied seismic interferometry using ambient noise to determine temporal changes in seismic velocity occurring at Laguna del Maule. Initial results show temporal changes in seismic velocity correlated to seasonal changes in the hydrologic cycle (rain, snow pack, snow melt, etc.). Current work focuses on identifying changes in seismic velocity associated with ongoing volcanic processes.

  17. Explore Seismic Velocity Change Associated with the 2010 Kaohsiung Earthquake by Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Ku, Chin-Shang; Wu, Yih-Min; Huang, Bor-Shouh; Huang, Win-Gee; Liu, Chun-Chi

    2016-04-01

    A ML 6.4 earthquake occurred on 4 March 2010 in Kaohsiung, the southern part of Taiwan, this shallow earthquake is the largest one of that area in the past few years. Some damages occurred on buildings and bridges after the earthquake, obvious surface deformation up to few cm was observed and the transportation including road and train traffic was also affected near the source area. Some studies about monitoring the velocity change induced by the big earthquake were carried out recently, most of studies used cross-correlation of the ambient noise-based method and indicated velocity drop was observed immediately after the big earthquake. However, this method is not able to constrain the depth of velocity change, and need to assume a homogeneous seismic velocity change during the earthquake. In this study, we selected 25 broadband seismic stations in the southern Taiwan and time period is from 2009/03 to 2011/03. Then we explored the velocity change associated with the 2010 Kaohsiung earthquake by applying ambient noise tomography (ANT) method. ANT is a way of using interferometry to image subsurface seismic velocity variations by using surface wave dispersions extracted from the ambient noise cross-correlation of seismic station-pairs, then the 2-D group velocity map with different periods could be extracted. Compare to ambient noise-based cross-correlation analysis, we estimated sensitivity kernel of dispersion curves and converted 2-D group velocity map from "with the period" to "with the depth" to have more constraints on the depth of velocity change. By subtracting shear velocity between "before" and "after" the earthquake, we could explore velocity change associated with the earthquake. Our result shows velocity reduction about 5-10% around the focal depth after the 2010 Kaohsiung earthquake and the post-seismic velocity recovery was observed with time period increasing, which may suggest a healing process of damaged rocks.

  18. Tectonic tremor and brittle seismic events triggered along the Eastern Denali Fault in northwest Canada

    NASA Astrophysics Data System (ADS)

    Zimmerman, J. P.; Aiken, C.; Peng, Z.

    2013-12-01

    Deep tectonic tremor has been observed in a number of plate-bounding tectonic environments around the world. It can occur both spontaneously (i.e. ambient) and as a result of small stress perturbations from passing seismic waves (i.e. triggered). Because tremor occurs beneath the seismogenic zone (> 15 km), it is important to understand where and how tremor occurs to discern its relationship with shallower earthquakes. In this study, we search for triggered tremor and brittle seismic events along the Eastern Denali Fault (EDF) in northwest Canada, an intraplate strike-slip region where previously tremor has not been observed. We retrieve seismic data for 19 distant earthquakes from 9 broadband stations monitored by the Canadian National Seismograph Network (CNSN). We apply high-pass or band-pass filters to the seismic data to suppress signals from distant events and search for local sources. Triggered tremor signals exhibit high-frequency contents, have long duration (> 15 s), are coincident with passing surface waves of the distant earthquakes, and are observable among nearby stations. Using this simple approach, we have identified 4 mainshocks that triggered tremor in our study region: the 2011/03/11 Mw9.1 Tohoku, 2012/04/11 Mw8.6 Sumatra, 2012/10/28 Mw7.7 Haida Gwaii, and 2013/01/05 Mw7.5 Craige earthquakes. Our initial locations indicate that the tremor source occurs on or near the southeastern portion of the EDF near the fault trace. In addition to the triggered tremor sources, we also identified many 'brittle' events with very short durations triggered by the Rayleigh waves of the 2012/10/28 Mw7.7 Haida Gwaii earthquake. While we were unable to locate these brittle events, they appear to be seismically similar to triggered icequakes observed in Antarctica (Peng et al., 2013) and occur during the dilatational strain changes caused by the Rayleigh waves.

  19. Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

    NASA Astrophysics Data System (ADS)

    Becker, D.; Meier, T.; Bohnhoff, M.; Harjes, H.-P.

    2010-04-01

    We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete and surrounding islands. More than 2,500 local and regional events with magnitudes up to M L = 4.5 were recorded during the time period July 2003-June 2004. The magnitude of completeness varies between 1.5 on Crete and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were observed. The plate

  20. Integration of onshore and offshore seismological data to study the seismicity of the Calabrian Region

    NASA Astrophysics Data System (ADS)

    D'Alessandro, Antonino; Guerra, Ignazio; D'Anna, Giuseppe; Gervasi, Anna; Harabaglia, Paolo; Luzio, Dario; Stellato, Gilda

    2014-05-01

    -land seismic stations. The lack of offshore stations prevents accurate determination of the hypocentral parameters also for moderate-strong earthquakes that occur in the Calabria offshore. With the aim of investigate the near shore seismicity in the Sibari Gulf and its eventual relationship with the Pollino activity, in the early 2014 will start a project for the improvement of the Calabrian Seismic Network in monitoring the Sibari Gulf area by deploying several Ocean Bottom Seismometers with Hydrophone (OBS/H). For this experiment, each OBS/H is equipped with a broad-band seismometer housed in a glass sphere designed to operate at a depth of up to 6000 m and with an autolevelling sensor system. The OBS/Hs are also equipped with an hydrophone. Analogical signals are recorded with a sampling frequency of 200 Hz by a four-channel 21 bits datalogger. In this work, we plan to present the preliminary results of the monitoring campaign showing the largest improvement in hypocenter locations derived from the integration of the onshore and offshore seismic stations.

  1. Cataloguing Seismic Waveform Properties Recorded With a 3D Network in a Gold Mine in South Africa

    NASA Astrophysics Data System (ADS)

    Julia, J.; Nyblade, A. A.; Gok, R.; Walter, W. R.; Linzer, L.; Durrheim, R. J.; Dirks, P.

    2007-12-01

    The SAVUKA gold mine is located in the northwestern edge of the Witwatersrand basin, a Late Archean (3.07- 2.71~Ga) intracratonic basin in South Africa that hosts the largest known gold-uranium-pyrite ore deposits in the world. Seismic events related to the mine activity span several orders of magnitude through a variety of sources that include mine blasts, pillar collapses, and faulting events. These events are systematically recorded and catalogued through an in-mine, 3D seismic network consisting of 20, three-component, short-period stations with natural frequencies ranging between 4.5 and 28.0~Hz and deployed as deep as ~3.5 km. After 5 months of seismic monitoring of the mine, we have been able to assemble a database of over 6000 events spanning magnitudes in the -2.5 < ML < 4.4 range. The potential of this unique data set for characterizing the detailed seismic properties of the basin and studying source properties of non-double couple events is explored through simple, first-pass analysis on the recorded waveforms. Moreover, the in-mine network is complemented by a small array of 4 broadband stations interspaced ~10~km apart on the surface of the mine, and by a number of AfricaArray stations in South Africa and neighboring countries located at regional distances (50- 1000~km) from the mine. The largest mine-induced events are clearly recorded at distances as far away from the mine as 450~km and provide a unique opportunity for studying the regional propagation of seismic phases as well as the structure of the cratonic crust underlying the basin.

  2. Long-period seismic amplification in the Kanto Basin from the ambient seismic field

    NASA Astrophysics Data System (ADS)

    Denolle, Marine A.; Miyake, Hiroe; Nakagawa, Shigeki; Hirata, Naoshi; Beroza, Gregory C.

    2014-04-01

    Tokyo, like many seismically threatened cities, is situated atop a sedimentary basin that has the potential to trap and amplify seismic waves from earthquakes. We study amplification in the Kanto Basin by exploiting the information carried by the ambient seismic field. We use 375 seismic stations from the high sensitivity seismograph network across central Honshu as virtual sources and 296 seismic stations of the Metropolitan Seismic Observation network shallow borehole seismometers within the basin as receivers to map the basin response. We find a linear relationship between ground motion and basin depth at periods of 2-10 s that could be used to represent 3-D basin effects in ground motion prediction equations. We also find that the strength of basin seismic amplification depends strongly on the direction of illumination by seismic waves.

  3. Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

    NASA Astrophysics Data System (ADS)

    Haldar, C.; Kumar, P.; Kumar, M. Ravi

    2014-05-01

    Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P-to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stations reveal that the Moho depth varies between ~ 10 ± 1 km and ~ 20 ± 1 km with the depths of the lithosphere-asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

  4. Seismic Activity at tres Virgenes Volcanic and Geothermal Field

    NASA Astrophysics Data System (ADS)

    Antayhua, Y. T.; Lermo, J.; Quintanar, L.; Campos-Enriquez, J. O.

    2013-05-01

    The volcanic and geothermal field Tres Virgenes is in the NE portion of Baja California Sur State, Mexico, between -112°20'and -112°40' longitudes, and 27°25' to 27°36' latitudes. Since 2003 Power Federal Commission and the Engineering Institute of the National Autonomous University of Mexico (UNAM) initiated a seismic monitoring program. The seismograph network installed inside and around the geothermal field consisted, at the beginning, of Kinemetrics K2 accelerometers; since 2009 the network is composed by Guralp CMG-6TD broadband seismometers. The seismic data used in this study covered the period from September 2003 - November 2011. We relocated 118 earthquakes with epicenter in the zone of study recorded in most of the seismic stations. The events analysed have shallow depths (≤10 km), coda Magnitude Mc≤2.4, with epicentral and hypocentral location errors <2 km. These events concentrated mainly below Tres Virgenes volcanoes, and the geothermal explotation zone where there is a system NW-SE, N-S and W-E of extensional faults. Also we obtained focal mechanisms for 38 events using the Focmec, Hash, and FPFIT methods. The results show normal mechanisms which correlate with La Virgen, El Azufre, El Cimarron and Bonfil fault systems, whereas inverse and strike-slip solutions correlate with Las Viboras fault. Additionally, the Qc value was obtained for 118 events. This value was calculated using the Single Back Scattering model, taking the coda-waves train with window lengths of 5 sec. Seismograms were filtered at 4 frequency bands centered at 2, 4, 8 and 16 Hz respectively. The estimates of Qc vary from 62 at 2 Hz, up to 220 at 16 Hz. The frequency-Qc relationship obtained is Qc=40±2f(0.62±0.02), representing the average attenuation characteristics of seismic waves at Tres Virgenes volcanic and geothermal field. This value correlated with those observed at other geothermal and volcanic fields.

  5. The Case for Broadband Evangelism

    ERIC Educational Resources Information Center

    Augustson, J. Gary; Roberts, Mike

    2004-01-01

    Higher education has an important stake in the national effort to widely deploy a state-of-the-art broadband public network. The Broadband Policy Group (BPG) developed a set of three principles to provide a consistent frame of reference for pursuing policy initiatives: (1) affordable broadband access; (2) a new regulatory structure; and (3)…

  6. Operating a global seismic network - perspectives from the USGS GSN

    NASA Astrophysics Data System (ADS)

    Gee, L. S.; Derr, J. S.; Hutt, C. R.; Bolton, H.; Ford, D.; Gyure, G. S.; Storm, T.; Leith, W.

    2007-05-01

    The Global Seismographic Network (GSN) is a permanent digital network of state-of-the-art seismological and geophysical sensors connected by a global telecommunications network, serving as a multi-use scientific facility used for seismic monitoring for response applications, basic and applied research in solid earthquake geophysics, and earth science education. A joint program of the U.S. Geological Survey (USGS), the National Science Foundation, and Incorporated Research Institutions in Seismology (IRIS), the GSN provides near- uniform, worldwide monitoring of the Earth through 144 modern, globally distributed seismic stations. The USGS currently operates 90 GSN or GSN-affiliate stations. As a US government program, the USGS GSN is evaluated on several performance measures including data availability, data latency, and cost effectiveness. The USGS-component of the GSN, like the GSN as a whole, is in transition from a period of rapid growth to steady- state operations. The program faces challenges of aging equipment and increased operating costs at the same time that national and international earthquake and tsunami monitoring agencies place an increased reliance on GSN data. Data acquisition of the USGS GSN is based on the Quanterra Q680 datalogger, a workhorse system that is approaching twenty years in the field, often in harsh environments. An IRIS instrumentation committee recently selected the Quanterra Q330 HR as the "next generation" GSN data acquisition system, and the USGS will begin deploying the new equipment in the middle of 2007. These new systems will address many of the issues associated with the ageing Q680 while providing a platform for interoperability across the GSN.. In order to address the challenge of increasing operational costs, the USGS employs several tools. First, the USGS benefits from the contributions of local host institutions. The station operators are the first line of defense when a station experiences problems, changing boards

  7. Tilt prior to explosions and the effect of topography on ultra-long-period seismic records at Fuego volcano, Guatemala

    NASA Astrophysics Data System (ADS)

    Lyons, John J.; Waite, Gregory P.; Ichihara, Mie; Lees, Jonathan M.

    2012-04-01

    Ground tilt is measured from broadband seismic records prior to frequent explosions at Fuego volcano, Guatemala. We are able to resolve tilt beginning 20-30 minutes prior to explosions, followed by a rapid reversal in deformation coincident with explosion onsets. The tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of Fuego appears to affect the ultra-long-period signals. We account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite-difference modeling. The results indicate a shallow spherical pressure source, and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography. The tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release.

  8. ACTS broadband aeronautical terminal

    NASA Technical Reports Server (NTRS)

    Agan, M. J.; Densmore, A. C.

    1995-01-01

    This paper discusses the design of, and experiments with, the ACTS Broadband Aeronautical Terminal. As part of the ongoing effort to investigate commercial applications of ACTS technologies, NASA's Jet Propulsion Laboratory and various industry/government partners are developing a broadband mobile terminal for aeronautical applications. The ACTS Broadband Aeronautical Terminal is designed to explore the use of K/Ka-band for high data rate aeronautical satellite communications. Currently available commercial aeronautical satellite communications systems are only capable of achieving data rates on the order of tens of kilobits per second. The broadband terminal used in conjunction with the ACTS mechanically steerable antenna, can achieve data rates of 384 kilobits per second, while use of an ACTS spot beam antenna with this terminal will allow up to T1 data rates (1.544 megabits per second). The aeronautical terminal will be utilized to test a variety of applications that require a high data rate communications link. The use of the K/Ka-band for wideband aeronautical communications has the advantages of spectrum availability and smaller antennas, while eliminating the one major drawback of this frequency band, rain attenuation, by flying above the clouds the majority of the time.

  9. Broadband simultaneous multiplane imaging

    NASA Astrophysics Data System (ADS)

    Blanchard, P. M.; Greenaway, A. H.

    2000-09-01

    A technique, using a distorted diffraction grating, which enables the simultaneous imaging of multiple object planes side-by-side on a single camera is described. The chromatic properties of the imaging system are discussed and a modification to allow operation with broadband illumination is demonstrated.

  10. The Acoustic Signal of a Helicopter can be Used to Track it With Seismic Arrays

    NASA Astrophysics Data System (ADS)

    Eibl, Eva P. S.; Lokmer, Ivan; Bean, Christopher J.; Akerlie, Eggert

    2016-04-01

    We apply traditional frequency domain methods usually applied to volcanic tremor on seismic recordings of a helicopter. On a volcano the source can be repeating, closely spaced earthquakes whereas for a helicopter the source are repeating pressure pulses from the rotor blades that are converted through acoustic-to-seismic coupling. In both cases the seismic signal is referred to as tremor. As frequency gliding is in this case merely caused by the Doppler effect, not a change in the source, we can use its shape to deduce properties of the helicopter. We show in this analysis that the amount of rotor blades, rotor revolutions per minute (RPM), flight direction, height and location can be deduced. The signal was recorded by a seven station broadband array with an aperture of 1.6 km. Our spacing is close enough to record the signal at all stations and far enough to observe traveltime differences. We perform a detailed spectral and location analysis of the signal, and compare our results with the known information on the helicopter's speed, location, height, the frequency of the blades rotation and the amount of blades. This analysis is based on the characteristic shape of the curve i.e. speed of the gliding, minimum and maximum fundamental frequency, amplitudes at the inflection points at different stations and traveltimes deduced from the inflection points at different stations. The helicopter GPS track gives us a robust way of testing the method. This observation has an educative value, because the same principles can be applied to signals in different disciplines.

  11. Seismic Investigations of the Zagros-Bitlis Thrust Zone

    NASA Astrophysics Data System (ADS)

    Gritto, R.; Sibol, M.; Caron, P.; Quigley, K.; Ghalib, H.; Chen, Y.

    2009-05-01

    We present results of crustal studies obtained with seismic data from the Northern Iraq Seismic Network (NISN). NISN has operated 10 broadband stations in north-eastern Iraq since late 2005. At present, over 800 GB of seismic waveform data have been analyzed. The aim of the present study is to derive models of the local and regional crustal structure of north and north-eastern Iraq, including the northern extension of the Zagros collision zone. This goal is, in part, achieved by estimating local and regional seismic velocity models using receiver function- and surface wave dispersion analyses and to use these velocity models to obtain accurate hypocenter locations and event focal mechanisms. Our analysis of hypocenter locations produces a clear picture of the seismicity associated with the tectonics of the region. The largest seismicity rate is confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases in the Bandar Abbas region again. Additionally, the rift zones in the Read Sea and the Gulf of Aden are clearly demarked by high seismicity rates. Our analysis of waveform data indicates clear propagation paths from the west or south-west across the Arabian shield as well as from the north and east into NISN. Phases including Pn, Pg, Sn, Lg, as well as LR are clearly observed on these seismograms. In contrast, blockage or attenuation of Pg and Sg-wave energy is observed for propagation paths across the Zagros-Bitlis zone from the south, while Pn and Sn phases are not affected. These findings are in support of earlier tectonic models that suggested the existence of multiple parallel listric faults splitting off the main Zagros fault zone in east-west direction. These faults appear to attenuate the crustal phases while the refracted phases, propagating across the mantle lid, remain unaffected. We will present surface wave analysis in support of these findings, indicating multi

  12. Seismicity and Crustal Anisotropy Beneath the Western Segment of the North Anatolian Fault: Results from a Dense Seismic Array

    NASA Astrophysics Data System (ADS)

    Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Cambaz, D.; Mutlu, A. K.; Kahraman, M.; Houseman, G. A.; Rost, S.; Thompson, D. A.; Cornwell, D. G.; Utkucu, M.; Gülen, L.

    2013-12-01

    The North Anatolian Fault (NAF) is one of the major strike slip fault systems on Earth comparable to San Andreas Fault in some ways. Devastating earthquakes have occurred along this system causing major damage and casualties. In order to comprehensively investigate the shallow and deep crustal structure beneath the western segment of NAF, a temporary dense seismic network for North Anatolia (DANA) consisting of 73 broadband sensors was deployed in early May 2012 surrounding a rectangular grid of by 70 km and a nominal station spacing of 7 km with the aim of further enhancing the detection capability of this dense seismic array. This joint project involves researchers from University of Leeds, UK, Bogazici University Kandilli Observatory and Earthquake Research Institute (KOERI), and University of Sakarya and primarily focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), receiver functions, moment tensor inversions, shear wave splitting, and ambient noise correlations. To begin with, we obtained the hypocenter locations of local earthquakes that occured within the DANA network. The dense 2-D grid geometry considerably enhanced the earthquake detection capability which allowed us to precisely locate events with local magnitudes (Ml) less than 1.0. Accurate earthquake locations will eventually lead to high resolution images of the upper crustal structure beneath the northern and southern branches of NAF in Sakarya region. In order to put additional constraints on the active tectonics of the western part of NAF, we also determined fault plane solutions using Regional Moment Tensor Inversion (RMT) and P wave first motion methods. For the analysis of high quality fault plane solutions, data from KOERI and the DANA project were merged. Furthermore, with the aim of providing insights on crustal anisotropy, shear wave splitting parameters such as lag time and fast polarization direction were obtained for local events recorded

  13. SKS anisotropy on a dense broadband array over the Ruby Mountains Metamorphic Core Complex, Nevada

    NASA Astrophysics Data System (ADS)

    Golos, E. M.; Litherland, M.; Klemperer, S. L.

    2012-12-01

    The Ruby Mountains metamorphic core complex (RMCC), located in the Basin-and-Range Province in northeastern Nevada, is thought to have formed by some combination of low-angle detachment faulting, lateral crustal flow, and vertical diapirism. We deployed a 50-station densely-spaced passive seismic array from June 2010 through June 2012, as part of the Earthscope Flexible Array campaign. We were particularly interested in determining whether two layers of anisotropy are distinguishable, as this could imply the existence of discrete crustal and mantle strain fabrics, and potentially provide insight into local flow involved in the formation of the RMCC. We analyzed SKS splitting using the SplitLab program (Wüstefeld et al., 2008, Comp. Geosci. 34, 515) to calculate fast-axis direction, Φ, and time delay, δt, of events with magnitude ≥ 5.50 at distances of 90 to 130 degrees on 35 of our broadband seismic stations. Approximately ten such events were used per station. The mean delay time found was 0.8 s with a standard deviation of 0.28 s, and the mean fast-axis azimuthal direction was -70.1 degrees with a standard deviation of 19 degrees. We did not find evidence of two-layer anisotropy beneath the Ruby Mountains: mean splitting times within and beyond the RMCC are well within one standard deviation of each other, and average fast directions show no obvious trend within the RMCC. Either there is no significant additional crustal strain associated with the RMCC formation; or, the strain direction is identical to that of regional mantle flow; or, most likely, our data quality is insufficient to resolve crustal anisotropy superimposed on mantle anisotropy with a potentially similar fast direction. However, a systematic counterclockwise rotation of fast-axis direction across our array—the four easternmost stations (D03, D02, B17, and C18) have a mean Φ = -40.5 degrees, whereas the four westernmost stations (D05, B01, B02, and C02) have a mean Φ = -79.5 degrees

  14. Seismic Anisotropy Beneath the Southern Puna Plateau

    NASA Astrophysics Data System (ADS)

    Calixto Mory, F. J.; Sandvol, E. A.; Kay, S. M.; Comte, D.; Alvarado, P. M.; Heit, B.; Yuan, X.

    2011-12-01

    The central Andean plateau offers an excellent natural laboratory to study mantle flow along an active continental margin as well as the link between plateau uplift and lithospheric delamination. The region between 25°S to 28°S, known as the southern Puna plateau, is characterized by a number of anomalous features possibly indicative of delamination. A total of 43 US and 30 German broadband three component seismic stations were deployed across the southern Puna plateau for approximately two years. The region of study has the advantage of deep and intermediate depth seismicity beneath the array that can be used to constrain the depth distribution of seismic anisotropy in the upper mantle. Teleseismic shear wave splitting results show a transition from east-west fast directions in the east of the array to east-west and north-south in the middle of the array, beneath Galan, and to predominantly north-south in the west part of the array. Azimuthal analysis of local events shows that the events coming from the North of the array split predominantely in the west-south north-east direction. The events coming from the south show splitting into the south-east north-west. Events coming from the West and East show predominant slab parallel splitting. Furthermore, a comparison of the teleseismic and local splitting lag times would suggest the presence of a significant amount of inter- or sub-slab anisotropy. Surface wave measurements indicate the presence of a high velocity block beneath Galan, a very large ignimbrite volcanic center, at depths between 190km (0.007 Hz) and 150 km (0.009 Hz). This can be interpreted as a delaminated block that has resulted in widespread crustal melting. At those same depths there are two high velocity zones, south east and north west of vicuña pampa. At 105 km (0.0125 Hz) we start to see the slab which seems to be deeping to the south. A low velocity zone further east could be responsible for the flatness of the slab at 26°S. At shallower

  15. Ambient seismic noise tomography of SW Iberia integrating seafloor- and land-based data

    NASA Astrophysics Data System (ADS)

    Corela, Carlos; Silveira, Graça; Matias, Luís; Schimmel, Martin; Geissler, Wolfram

    2016-04-01

    We used ambient seismic noise recorded by 24 broadband ocean bottom seismometers (OBS-BB) deployed in in the Gulf of Cadiz during the EC funded NEAREST project and seven broadband land stations located in the South of Portugal to image the sedimentary and crustal structure beneath the Eastern Atlantic and SW Iberia. We computed ambient noise cross-correlations to obtain empirical Green's functions (EGFs) between all station pairs, and using both sort of sensors, namely seismometers and hydrophones. Despite the great difference between the crustal structure below beneath OBSs and land stations and the recording conditions, we were able to compute high signal-to-noise ratio EGFs, by applying a linear cross-correlation with a running absolute mean average time normalization, followed by a time-frequency phase weighted stack. Dispersion analysis was then applied to the EGFs, between 4 and 20s period. The obtained 395 reliable group velocity dispersion curves, between all station pairs, allowed mapping the lateral variation of Rayleigh wave group velocities, as a function of period. Finally, dispersion curves extracted from each cell of the 2D group velocity maps were inverted, as a function of depth, to obtain the 3D distribution of the shear-wave velocities. The 3-D shear wave velocity model, computed from joint inversion of OBS and land stations data allowed to estimate the thickness of sediments and crust and the Moho depth. Although, we could perceive the impact of the spatial gap between OBSs and land stations, our model displays a good correlation with the main geological features. The main results on the sedimentary layer thickness and on the Moho depth are in agreement with the model proposed by other studies using observations from multi-beam bathymetry and seismic profiling, thus confirming that, not only that ambient noise tomography is a valuable tool to image oceanic domains, but also that we can integrate seafloor- and land-based stations. Publication

  16. Two-station phase velocity determination for structure in North Africa

    SciTech Connect

    Hazler, S; Pasyanos, M; Sheehan, A; Walter, W

    1999-07-28

    The seismic structure of North Africa is poorly understood due to the relative paucity of stations and seismicity when compared to other continental regions of the world. A better understanding of the velocity structure in this area will allow improved models of travel times and regional phase amplitudes. Such models will improve location and identification capability in this region leading to more effective monitoring of the Comprehensive Nuclear-Test-Ban Treaty. Using regional-to-teleseismic Rayleigh and Love waves that traverse the area we can obtain information about the region's seismic structure by examining phase velocity as a function of period. We utilize earthquakes from the tectonically active regions bounding North Africa (Mediterranean, Red Sea, East African Rift, and Mid-Atlantic Ridge) recorded at broadband seismic stations distributed throughout the region. A two-station method is utilized to determine phase velocity information along the interstation segment of the ray path. The two-station method provides particular advantage in this region as it dramatically increases the number of events available to provide pure North African sampling. Bandpass filters are applied to the seismograms so that peaks and troughs may be correlated. The phase is unwrapped and a difference curve computed. The difference curve is then converted to a phase velocity dispersion curve. Phase velocity curves are constructed in the range of 10 to 120 seconds. Rayleigh and Love waves in this period range are most sensitive to the shear velocity structure of the lithosphere and can be used in combination with additional independent seismic observations (e.g. Pn tomography, surface wave group velocity tomography, receiver functions, etc.) to construct reliable velocity models. We compare velocities computed in this study to those generated from well known models for similar tectonic regions throughout the world in order to better define the tectonic setting of North Africa

  17. Southern Africa seismic structure and source studies

    NASA Astrophysics Data System (ADS)

    Zhao, Ming

    1998-09-01

    The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data. Waveform and travel time data used in this study come mainly from a large mine tremor in South Africa (msb{b} 5.6) recorded on stations of the southern Africa and the Tanzania Broadband Seismic Experiment. Auxiliary data along similar profiles are obtained from other moderate events within eastern and southern Africa. The waveform data from the large tremor show upper mantle triplications for both the 400 and 670-km discontinuities between 18sp° and 27sp° distance. The most notable feature of the data is a large, late P phase that propagates to at least 27sp°. This phase is striking because of its late arrival time (as much as 15 seconds after direct P at 27sp°) and high amplitude relative to the first arrival. Travel times from all available stations are used to invert for the P wave velocity structure down to 800 km depth and S wave velocity structure down to 200 km using the Wiechert-Herglotz (W-H) inversion technique. The P wave velocities from the uppermost mantle down to 300 km are as much as 3% higher than the global average and are slightly slower than the global average between 300 and 400 km depths. The velocity gradient between 300 and 400 km is 0.0015 1/s. The S wave travel time data yield fast velocities above 200-km depth. The S wave velocity structure appears inconsistent with the P wave structure model indicating varying Poisson's ratio in the upper mantle. Little evidence is found for a pronounced upper mantle low velocity zone. Both sharp and gradual-change 400-km discontinuities are favored by the waveform data. The 670-km discontinuity appears as a gradual-change zone. The source mechanism of the mb 5.6 mining tremor itself is important for seismic discrimination and insight into mining tremor sources. Source parameters for this event as well as some other large mining tremors from the South African gold mines are studied

  18. Seismicity and Improved Velocity Structure in Kuwait

    SciTech Connect

    Gok, R M; Rodgers, A J; Al-Enezi, A

    2006-01-26

    The Kuwait National Seismic Network (KNSN) began operation in 1997 and consists of nine three-component stations (eight short-period and one broadband) and is operated by the Kuwait Institute for Scientific Research. Although the region is largely believed to be aseismic, considerable local seismicity is recorded by KNSN. Seismic events in Kuwait are clustered in two main groups, one in the south and another in the north. The KNSN station distribution is able to capture the southern cluster within the footprint of the network but the northern cluster is poorly covered. Events tend to occur at depths ranging from the free surface to about 20 km. Events in the northern cluster tend to be deeper than those in south, however this might be an artifact of the station coverage. We analyzed KNSN recordings of nearly 200 local events to improve understanding of seismic events and crustal structure in Kuwait, performing several analyses with increasing complexity. First, we obtained an optimized one-dimensional (1D) velocity model for the entire region using the reported KNSN arrival times and routine locations. The resulting model is consistent with a recently obtained model from the joint inversion of receiver functions and surface wave group velocities. Crustal structure is capped by the thick ({approx} 7 km) sedimentary rocks of the Arabian Platform underlain by normal velocities for stable continental crust. Our new model has a crustal thickness of 44 km, constrained by an independent study of receiver functions and surface wave group velocities by Pasyanos et al (2006). Locations and depths of events after relocation with the new model are broadly consistent with those reported by KISR, although a few events move more than a few kilometers. We then used a double-difference tomography technique (tomoDD) to jointly locate the events and estimate three-dimensional (3D) velocity structure. TomoDD is based on hypoDD relocation algorithm and it makes use of both absolute and

  19. Temporal Evolution of a Seismic Swarm at Chiles - Cerro Negro volcanic complex

    NASA Astrophysics Data System (ADS)

    Ruiz, Mario

    2015-04-01

    The increasing seismic activity in the area of the Chiles - Cerro Negro volcanic complex, located on the Ecuador-Colombian border, has been jointly monitored by the Instituto Geofisico - Ecuador and the Observatorio Vulcanologico y Sismologico de Pasto (OVSP), a division of the Servicio Geologico Colombiano. Since April 2013, three seismic swarms have been detected in this area, and more than 400.000 events have been recorded since November 2013. The largest and most recent swarm has a daily average of 3894 events between March and the 12th of December 2014. Currently a seismic network of 13 short- and broad-band stations (5 Colombian, 8 Ecuadorian) was deployed in this area. High quality epicenters of seismic events with magnitudes Ml>2.0, RMS<0.75 s, Gap < 180° and 10 or more phases are located in an area 1-4 km south of Chiles volcano with shallow depths (up to 14 km). Most events have magnitudes between 1.0 to 4.0. Fifteen events have magnitudes larger than 4.0 including an event that occurred on October 20, 2014. This event had a local magnitude of 5.7 and an oblique (strike-slip with some thrusting) focal mechanism. Waveforms and spectral patterns define these events as volcano-tectonic. However, events with moderate to large magnitudes (above 3.0) contain pronounced very-long-period components. Position time series recorded by a dual-frequency GPS receiver at the SE flank of Chiles show a slight departure from the normal tectonic trend beginning with the appearance of the last seismic swarm on or around September 30, 2014. This trend is subsequently punctuated by a sharp deformation transient related to the coseismic displacement of the October 20 event. After more than a year of very anomalous seismic activity and concurrent minor deformation, no evidence of surficial volcanic activity has been documented.

  20. Seismicity of Dronning Maud Land/antarctica As Detected By The Neumayer Seismological Array

    NASA Astrophysics Data System (ADS)

    Eckstaller, A.; Mueller, C.; Hoffmann, M.

    Array seismology provides a powerful tool for improving detection and localization capabilities for monitoring weak seismic events. Little is known about seismic activity of the Antarctic continent due to the sparse station deployment of the global network in this region. To improve monitoring capabilities a small-aperture short-period detec- tion array was installed in the vicinity of the German base Neumayer/Dronning Maud Land. The array complements the Neumayer seismograph network and the broadband seismograph SNAA at the neighbouring South African base Sanae IV. The array was installed in the austral summer season 1997 and has been operational almost continu- ously since that time. The design was adopted from the SPITS-array in Svalbard and consists of 15 short-period vertical seismometers arranged on three concentric rings around the 3-component intermediate-period seismometer in the center. Event detec- tion and beamforming is done automatically using array processing software from NORSAR. With this seismic antenna the number of detected Antarctic earthquakes was increased significantly. In particular, two seismically active regions were identified along the Jutul-Penck-Graben and off Kapp Norvegia. The nature of this seismic activity is not yet fully understood. Especially, the Jutul-Penck-Graben region is of interest since the question arises if this is an active tectonic rift system or if the seismic activity origi- nates from post-glacial rebound movements. Better knowledge of hypocentral depths and focal mechanisms will contribute to the understanding of these mechanisms. An integrated approach by using temporary local networks including geodetical and air- borne geophysical measurements may reveal the mechanisms of these neotectonic dynamics.

  1. The Irpinia Seismic Network (ISNet): hardware and data management

    NASA Astrophysics Data System (ADS)

    Iannaccone, G.

    2009-04-01

    The Irpinia Seismic Network, operating in southern Italy, is primarily aimed at providing an alert for moderate to large earthquakes in selected target sites in the Campania Region, and it also provides data for rapid computation of regional ground-shaking maps. ISNet is deployed over the active seismic faults system of Irpinia, southern Italy. It features 28 seismic stations and 5 data processing sites (local control centers - LCC). All stations are equipped with a strong-motion accelerometer and a three component velocimeter, with a one second natural period, for a high dynamic recording range. Five stations host broadband sensors, for recording regional and teleseismic events. The recorded seismic data are sent from each station to the nearby LCC, through a Wi-Fi directional antenna, in SeedLink format. Each LCC runs: the SeisComP software, to relay the data to outside SeedLink clients; the Earthworm system, for real-time processing (e.g. to produce a bulletin of automatically detected events); the Winston software, for data storage and visualization. To monitor and maintain all of the described ISNet instrumentation, and to access, analyze and edit the seismic data produced, we developed a software application, SeismNet Manager, that implements a web-based user interface to a database of all the ISNet information and data. For early warning applications, a high bandwidth radio links backbone is being deployed, interconnecting the LCCs and the Network Control Center in Naples. We developed a software application that processes the live streams of 3-component acceleration from the stations and, while an energetic event is occurring, promptly performs picking, event detection, event location and magnitude estimation. The earthquake location uses an evolutionary, real-time technique based on an equal differential time (EDT) formulation, and a probabilistic approach for describing the hypocenter. This algorithm, at each time step, relies on both the information from

  2. 3-D Modeling for Upper Mantle Anisotropy Beneath Idaho-Oregon (IDOR) Region Using Sks Splitting Intensity Measurements from IDOR Passive Seismic Project Dataset

    NASA Astrophysics Data System (ADS)

    Hongsresawat, S.; Panning, M. P.; Russo, R. M.; Mocanu, V. I.; Stanciu, A. C.; Bremner, P. M.; Torpey, M. E.; VanDecar, J. C.

    2014-12-01

    We used data recorded at 86 broadband seismic stations of the IDOR Passive Seismic Project to determine upper mantle anisotropy across the suture along which Blue Mountain island-arc terranes accreted to North America during Cretaceous. This suture is currently associated with the Western Idaho Shear Zone (WISZ), a narrow, highly-deformed ductile fault that was the locus of both dextral strike-slip along, and subduction beneath, the Paleozoic margin of the North American craton. We measured shear wave splitting intensity (SI), a seismic observable that is suitable for use in 3-D inversions of upper mantle seismic anisotropy, to determine these fabrics beneath the IDOR network. SI fast-polarization directions are spatially coherent across the region, and fall into three main groups: a group with fast azimuths trending ENE-WSW, observed at stations in eastern Oregon and the NW-SE-striking western Snake River Plain; a group with E-W trending fast azimuths observed at stations along the WISZ and the Idaho Batholith, which outcrops immediately east of the suture zone; and a group with ENE-WSW trending fast azimuths observed at stations situated in the Basin-and-Range extended region of southeastern Idaho. SI delay times range from 0.46 to 1.85 seconds, with a mean of 1.1 s. We also used backazimuthal variations of SI at all stations to invert for for 3-D anisotropic fabric using the finite-frequency approach called vectorial tomography (Chevrot and Monteiller, 2009). Our preliminary results are consistent with alignment of upper mantle fabrics in the extension direction as Basin-and-Range extension propagates northward into less-extended regions of Idaho and Oregon.

  3. EMERALD: Coping with the Explosion of Seismic Data

    NASA Astrophysics Data System (ADS)

    West, J. D.; Fouch, M. J.; Arrowsmith, R.

    2009-12-01

    The geosciences are currently generating an unparalleled quantity of new public broadband seismic data with the establishment of large-scale seismic arrays such as the EarthScope USArray, which are enabling new and transformative scientific discoveries of the structure and dynamics of the Earth’s interior. Much of this explosion of data is a direct result of the formation of the IRIS consortium, which has enabled an unparalleled level of open exchange of seismic instrumentation, data, and methods. The production of these massive volumes of data has generated new and serious data management challenges for the seismological community. A significant challenge is the maintenance and updating of seismic metadata, which includes information such as station location, sensor orientation, instrument response, and clock timing data. This key information changes at unknown intervals, and the changes are not generally communicated to data users who have already downloaded and processed data. Another basic challenge is the ability to handle massive seismic datasets when waveform file volumes exceed the fundamental limitations of a computer’s operating system. A third, long-standing challenge is the difficulty of exchanging seismic processing codes between researchers; each scientist typically develops his or her own unique directory structure and file naming convention, requiring that codes developed by another researcher be rewritten before they can be used. To address these challenges, we are developing EMERALD (Explore, Manage, Edit, Reduce, & Analyze Large Datasets). The overarching goal of the EMERALD project is to enable more efficient and effective use of seismic datasets ranging from just a few hundred to millions of waveforms with a complete database-driven system, leading to higher quality seismic datasets for scientific analysis and enabling faster, more efficient scientific research. We will present a preliminary (beta) version of EMERALD, an integrated

  4. Preliminary Results of Crustal Structure beneath the Wabash Valley Seismic Zone Using Teleseismic Receiver Functions and Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Zhu, L.; Aziz Zanjani, A.; Hu, S.; Liu, Y.; Herrmann, R. B.; Conder, J. A.

    2015-12-01

    As part of a on-going EarthScope FlexArray project, we deployed 45 broadband seismographs in a 300-km-long linear profile across the Wabash Valley Seismic Zone (WVSZ). Here we present preliminary results of crustal structure beneath WVSZ based on teleseismic receiver functions and ambient noise tomography. We combined waveform data of the temporary stations in 2014 with those of permanent seismic stations and the transportable array stations in our study area since 2011. We found 656 teleseismic events with clear P-wave signals and obtained 2657 good-quality receiver functions of 84 stations using a time-domain iterative deconvolution method. We estimated crustal thickness and Vp/Vs ratio beneath each station using the H-κ stacking method. A high-resolution crustal structural image along the linear profile was obtained using the Common-Conversion-Point (CCP) stacking method. We also measured Rayleigh-wave phase and group velocities from 5 to 50 s by cross-correlating ambient noises between stations and did joint-inversion of receiver functions and surface wave dispersions for S-velocity structures beneath selected stations. The results show that the average crustal thickness in the region is 47 km with a gentle increase of crustal thickness from southeast to northwest. A mid-crustal interface is identified in the CCP image that also deepens from 15 km in the southeastern end to >20 km in the northwest. The CCP image shows that the low-velocity sedimentary layer along the profile is broad and is thickest (~10 km) near the center of the Wabash Valley. Beneath the center of the Valley there is a 40-km-wide positive velocity discontinuity at a depth of 40 km in the lower crust that might be the top of a rift pillow in this failed continental rift. Further results using 3D joint inversion and CCP migration will be presented at the meeting.

  5. Estimating site effects for seismic hazard assessment in Portugal using shear wave and geotechnical data

    NASA Astrophysics Data System (ADS)

    Cancela Pinto, C.; Carvalho, J.; Vilanova, S.; Borges, J.

    2012-04-01

    The estimation of seismic ground motion requires a simultaneous understanding of the effects of earthquake sources, propagation effects in the earth and local geological site conditions. In this work we address the latter issue in Portugal mainland. The SCENE project has the main goal to improve the seismic hazard assessment in Portugal by taking into account the site effects. To achieve this purpose, the project was divided into two main goals: 1) to estimate the shear-wave profiles at the seismic stations in order to correct the recorded ground motions for site effects and 2)to produce a regional soil classification based on shear-wave velocity averaged on the upper 30m (VS30) that will be used to include first order site effects in seismic hazard maps. This parameter was calculated using seismic refraction and reflection data, interpreted with the aid of nearby wells. The refraction interpretation was carried out using the generalized reciprocal and first break tomographic methods. Using reflection seismic software, the velocities measured from the reflection hyperbolae occasionally observed in the shot gathers were used to obtain an average velocity until the respective reflector and complement the refraction data. The soil classification is based on the eurocode 8, which uses only shear wave velocities, but the classification presented here includes also standard penetration test (SPT) data. The seismic acquisition was carried out next to the accelerometer and broadband stations located in the regions center and south of Portugal. To produce a soil classification, 30 P-wave and 30 S-wave profiles were acquired and data collected under the scope of other projects was also used. The classification takes into consideration not only the geological units on which the seismic profiles were acquired but lithological information and has been generalized to each unit using 1: 200.000 scale geological cartography. This classification for southern Portugal is presented

  6. Effects of heterogeneities on the propagation, scattering and attenuation of seismic waves and the characterization of seismic source. Final report, 1 December 1982-30 November 1985

    SciTech Connect

    Aki, K.; Cormier, V.F.; Toksoz, M.N.

    1985-01-01

    During this reporting period, work was completed on testing alternative measures of body-wave magnitude. It was found that alternative measures of body waves magnitude often exhibit as much scatter as classical measures of magnitude, although coda magnitudes usually have slightly less scatter than spectral and classical magnitudes. In the cases investigated, these differences were usually not statistically significant. Another completed task was an investigation of the intrinsic attenuation of the Earth's mantle selected paths from the Sea of Okhotsk to Regional Seismic Test Network (RSTN) and Global Digital Seismic Network (GDSN) Stations in North America. It was concluded that the intrinsic attenuation in the mantle beneath eastern North America is both depth and frequency dependent and that spectral and time domain studies of attenuation can be reconciled in the frequency band up to 2 Hz. The focus of the project was then divided between source problems related to scattering and seismic wave propagation in three-dimensional, heterogeneous media. A significant result was that short period and broadband waveforms can improve the depth-resolution-determined earthquakes and underground nuclear explosions, forming a powerful discriminant. Scattering was studied theoretically and observationally. The significant result of that work is that the Earth's lithosphere must possess multiple scales of heterogeneity in order to explain both the amplitude and phase fluctuations at large arrays as well as the shapes of local S coda.

  7. Upper-Mantle Anisotropy from SKS Splitting on a Dense Broadband Profile Across the Salton Trough, Southern California

    NASA Astrophysics Data System (ADS)

    Kinsella, A. B.; Barak, S.; Klemperer, S. L.

    2012-12-01

    Alex Kinsella, Shahar Barak, and Simon L. Klemperer Stanford University The Salton Trough is an active magma-dominated rift linking the Gulf of California to the San Andreas fault system. Because the rift is buried beneath a thick pile of Colorado River sedimentary rock, surprisingly little is currently known about the total volume of intrusion into the crust and the magma distribution within and beyond the rift margins. Our Broadband Salton Seismic Imaging Project, part of the larger USGS-NSF SSIP (Salton Seismic Imaging Project), deployed 42 broadband seismographs from 2011 to 2013 across the Salton Trough from San Diego to the Colorado River. Thirty-six of the stations were deployed along a WSW-ENE line across the trough, while the other six stations were deployed off-line to provide areal coverage. Our broadband study is intended to lead to a better understanding of magmatic dominated rifts. We analyzed shear wave splitting of SKS and SKKS phases from earthquakes with moment magnitude greater than 5.5 at distances 90° to 145°. Preliminary single-layer models based on the largest magnitude events show fast axes aligned roughly east-west at stations in the Peninsular Ranges west of the Salton Trough, as recognized by many previous studies, while in the center and east of the trough, the fast axes are roughly NNW-SSE (parallel to the axis of the Salton Trough). Delay times on the western side of the trough range from 0.5 to 1.5 seconds, but stations on the eastern side of the trough have generally shorter delay times, clustering between 0.5 and 0.8 seconds. These relatively large delay times indicate the mantle is the dominant source of the anisotropy. The W-E anisotropy to the west has previously been interpreted as due to either movement of the trailing edge of the Farallon plate over the last 20 million years or Cenozoic N-S compression in southern California. The NNW-SSE fast axes, within and east of the trough, might be explained by NW-SE mantle flow due to

  8. Albuquerque Basin seismic network

    USGS Publications Warehouse

    Jaksha, Lawrence H.; Locke, Jerry; Thompson, J.B.; Garcia, Alvin

    1977-01-01

    The U.S. Geological Survey has recently completed the installation of a seismic network around the Albuquerque Basin in New Mexico. The network consists of two seismometer arrays, a thirteen-station array monitoring an area of approximately 28,000 km 2 and an eight-element array monitoring the area immediately adjacent to the Albuquerque Seismological Laboratory. This report describes the instrumentation deployed in the network.

  9. Seismic tomography reveals the upper-mantle structure beneath the Carpathian-Pannonian system

    NASA Astrophysics Data System (ADS)

    Dando, B. D.; Houseman, G.; Stuart, G. W.; Hegedus, E.; Kovacs, A.; Brueckl, E. P.; Hausmann, H.; Radovanovic, S.

    2009-12-01

    The Carpathian Basins Project (CBP) aims to understand the formation of the Miocene-age extensional basins contained within the convergent arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new tomographic determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from 232 teleseismic events. To avoid contamination of our inversion results from crustal velocity variations, deterministic corrections are applied to our travel-time residuals using crustal velocity models obtained from controlled source experiments and sediment thickness maps. Our 3-D velocity model images the fast velocity structure of the eastern Alps down to ~350 km. Beneath the Pannonian basin the velocity variation at 300 km depth is dominated by a fast region which extends eastward from the Alpine anomaly and reaches down into the mantle transition zone (MTZ). This fast structure is limited on the North side by slow material beneath the North Carpathians. At depths greater than 450 km, below the eastern Pannonian basin, a slow anomaly extends to the base of the model. Beneath the same region Hetenyi et al. (submitted to GRL), used receiver functions from the CBP dataset, to show a localised depression of the 660 km discontinuity of up to ~40 km. We aim to address how the depression of the 660 km discontinuity and its associated density and velocity variations affect our tomographic images. Our results will help to provide

  10. Using a Genetic Algorithm to Model Broadband Regional Waveforms for Crustal Structure in the Western United States

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Joydeep; Sheehan, Anne F.; Tiampo, Kristy; Rundle, John

    1999-01-01

    In this study, we analyze regional seismograms to obtain the crustal structure in the eastern Great Basin and western Colorado plateau. Adopting a for- ward-modeling approach, we develop a genetic algorithm (GA) based parameter search technique to constrain the one-dimensional crustal structure in these regions. The data are broadband three-component seismograms recorded at the 1994-95 IRIS PASSCAL Colorado Plateau to Great Basin experiment (CPGB) stations and supplemented by data from U.S. National Seismic Network (USNSN) stations in Utah and Nevada. We use the southwestern Wyoming mine collapse event (M(sub b) = 5.2) that occurred on 3 February 1995 as the seismic source. We model the regional seismograms using a four-layer crustal model with constant layer parameters. Timing of teleseismic receiver functions at CPGB stations are added as an additional constraint in the modeling. GA allows us to efficiently search the model space. A carefully chosen fitness function and a windowing scheme are added to the algorithm to prevent search stagnation. The technique is tested with synthetic data, both with and without random Gaussian noise added to it. Several separate model searches are carried out to estimate the variability of the model parameters. The average Colorado plateau crustal structure is characterized by a 40-km-thick crust with velocity increases at depths of about 10 and 25 km and a fast lower crust while the Great Basin has approximately 35- km-thick crust and a 2.9-km-thick sedimentary layer.

  11. Future large broadband switched satellite communications networks

    NASA Technical Reports Server (NTRS)

    Staelin, D. H.; Harvey, R. R.

    1979-01-01

    Critical technical, market, and policy issues relevant to future large broadband switched satellite networks are summarized. Our market projections for the period 1980 to 2000 are compared. Clusters of switched satellites, in lieu of large platforms, etc., are shown to have significant advantages. Analysis of an optimum terrestrial network architecture suggests the proper densities of ground stations and that link reliabilities 99.99% may entail less than a 10% cost premium for diversity protection at 20/30 GHz. These analyses suggest that system costs increase as the 0.6 power of traffic. Cost estimates for nominal 20/30 GHz satellite and ground facilities suggest optimum system configurations might employ satellites with 285 beams, multiple TDMA bands each carrying 256 Mbps, and 16 ft ground station antennas. A nominal development program is outlined.

  12. Characterizing Seismic Anisotropy across the Peruvian Flat-Slab Subduction Zone: Shear Wave Splitting from PULSE

    NASA Astrophysics Data System (ADS)

    Eakin, C. M.; Long, M. D.; Beck, S. L.; Wagner, L. S.; Tavera, H.

    2013-12-01

    Although 10% of subduction zones worldwide today exhibit shallow or flat subduction, we are yet to fully understand how and why these slabs go flat. An excellent study location for such a problem is in Peru, where the largest region of flat-subduction currently exists, extending ~1500 km in length (from 3 °S to 15 °S) and ~300 km in width. Across this region we investigate the pattern of seismic anisotropy, an indicator for past and/or ongoing deformation in the upper mantle. To achieve this we conduct shear wave splitting analyzes at 40 broadband stations from the PULSE project (PerU Lithosphere and Slab Experiment). These stations were deployed for 2+ years across the southern half of the Peruvian flat-slab region. We present detailed shear wave splitting results for deep and teleseismic events, making use of a wide variety of available phases that sample the upper mantle directly beneath the stations (such as SKS, SKKS, PKS, sSKS, SKiKS, ScS and local/direct S). We analyze the variability of our results with respect to initial polarizations and ray paths, as well as spatial variability between stations as the underlying slab morphology changes. Preliminary results show predominately NW-SE fast polarizations (trench oblique to sub-parallel) over the flat-slab region east of Lima. These results are consistent with observations of more complex multi-layered anisotropy beneath a nearby permanent station (NNA). Further south, towards the transition to steeper subduction, the splitting pattern becomes increasingly dominated by null measurements. Over to the east however, beyond Cuzco, where the mantle wedge might begin to play a role, we record fast polarizations quasi-parallel to the local slab contours. We carefully evaluate the different possible source locations within the subduction zone for this seismic anisotropy and observe increasing evidence for distinct anisotropy within the slab as well as the sub-slab mantle.

  13. SEISMIC SOURCE AND PATH CALIBRATION IN THE KOREAN PENINSULA, YELLOW SEA

    SciTech Connect

    Herrmann, R B; Walter, W R; Pasyanos, M

    2007-07-11

    Two significant seismic events were analyzed using the crustal velocity model developed under this contract. The M{sub W} = 4.55 Korea earthquake of January 20, 2007 occurred in the Republic of Korea on land and within the dense digital seismic network. Using P-wave arrivals from 60 broadband, short-period and acceleration stations, the event occurred at 37.68N, 128.58E at a depth of 7.5 km at 20070120115653.8. Source inversion was performed using the accelerometer recordings in the 0.05-0.20 Hz band the broadband data in the 0.02-0.10 Hz band, with identical focal mechanisms and source depths of 9 and 11 km, respectively. This is the largest event on land in South Korea since the M{sub W} 4.7 event on December 13, 1996. Forward modeling of the waveforms at INCN and MDJ indicates the ability of the current model to match observations on the Korean Peninsula and the effect of significant pulse shape modification for paths that partially cross the Sea of Japan. The results of using the local network data provide a ground truth point for other studies analyzing seismic events on the peninsula. The isotropic seismic moment of the October 9, 2006 North Korea explosion was estimated from the Rayleigh-wave spectral amplitudes observed at MDJ and INCN. Very little Love wave signal was observed, indicating weak tectonic release. The explosion yield was investigated using the Denny and Johnson (1991) model relating yield to the observed isotropic moment as a function of depth of burial and material properties. Sensitivity analysis highlights the strong effect of the assumed velocity and density structure in the upper kilometer of the Earth and the assumed depth of burial on the estimated yield. The crustal velocity model developed under this contract provides strong constraints on the expected shear-wave velocities in the shallow parts of the crust. Issues to be investigated include the effect of wave propagation through the Eastern Sea (Sea of Japan) to stations in South

  14. New seismic study begins in Puerto Rico

    USGS Publications Warehouse

    Tarr, A.C.

    1974-01-01

    A new seismological project is now underway in Puerto Rico to provide information needed for accurate assessment of the island's seismic hazard. The project should also help to increase understanding of the tectonics and geologic evolution of the Caribbean region. The Puerto Rico Seismic Program is being conducted by the Geological Survey with support provided by the Puerto Rico Water Resources Authority, an agency responsible for generation and distribution of electric power throughout the Commonwealth. The Program will include the installation of a network of high quality seismograph stations to monitor seismic activity on and around Puerto Rico. These stations will be distributed across the island to record the seismicity as uniformly as possible. The detection and accurate location of small earthquakes, as well as moderate magnitude shocks, will aid in mapping active seismic zones and in compiling frequency of occurrence statistics which ultimately wil be useful in seismic risk-zoning of hte island. 

  15. Watching the wind: seismic data contamination at long-periods due to atmospheric pressure-field-induced tilting

    NASA Astrophysics Data System (ADS)

    de Angelis, S.; Bodin, P.; Hagel, K.; Fletcher, D.

    2010-12-01

    Long-period noise generated by the elastic response of the Earth to atmospheric pressure fluctuations has long been recognized as a limiting factor for seismic investigations. The quality of seismic data recorded by sensitive, near-surface broadband seismometers can be severely corrupted by this effect. During the recent installation of a new broadband site on the Olympic Peninsula in Washington, the Pacific Northwest Seismic Network recorded and investigated elevated daytime noise levels at periods exceeding 30 seconds. Substantial power spectral density variations of the background noise field, 15-20 dB, were observed in the horizontal component seismograms. The pattern of the long-period noise exhibited striking correlations with local fluctuations of the air temperature and wind speed as measured nearby the seismic station by the National Weather Service Forecast Office, Seattle, Washington, and the National Oceanic and Atmospheric Administration. Several past studies have demonstrated that local wind systems may lead to variations of the atmospheric pressure field that deform the ground and perturb seismograms. The rotational component of this motion is detected by horizontal-component seismometers because at periods longer than the sensor’s low corner frequency the sensor is acting essentially as a tiltmeter. We obtained a transfer function that describes the response of the broadband seismometer to a tilt step change and estimated the amplitude of tilt noise to be on the order of 10-9 - 10-8 radians. Within the seismic pass-band of the sensor, it is not possible to remove the tilt signal from the observed seismograms because the details of the tilting depend on the pressure field variations, the compliance of the near surface to pressure variations, and the design and construction of the seismometer vault itself. At longer periods, using the seismic data to recover tilts of tectonic origin is made challenging because of the needed instrument correction

  16. Field Report on the iMUSH Active Source Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Kiser, E.; Levander, A.; Schmandt, B.; Palomeras, I.; Harder, S. H.; Creager, K. C.; Vidale, J. E.; Malone, S. D.

    2014-12-01

    In the second half of July we completed the iMUSH active source seismic experiment, one component of the Imaging Magma Under Saint Helens project. A team of ~75 volunteers deployed 3500 seismographs to ~5920 locations on and around Mount St. Helens over the course of 3 weeks. This instrument deployment was accompanied by 23 shots distributed around the volcano. Instrumentation consisted of ~2550 Reftek 125A (Texan) seismographs with 4.5 Hz geophones, and 920 Nodal Seismic recorders with 10 Hz geophones. The shots were also recorded by the permanent stations of the Pacific Northwest Seismograph Network and 70 iMUSH broadband seismographs. Fifteen of the shots, 424 kg each, formed two rings around Mount Saint Helens at 15 km and 30 km radius from the summit. Eight of the shots, 828 kg each, were fired at distances of 50 to 80 km from MSH on NW-SE and NE-SW azimuths. The deployment geometry consisted of two lines oriented NW/SE and NE/SW, and three arrays. The offset of the lines ranged from 150 km to 190 km with an average spacing of 200 m. The first array was centered on the volcano with a radius of 30 km, and required both driving and hiking to deploy. Arrays two and three were set out with, and centered on, the NW/SE line. These arrays had a distance range from MSH of 30-75 km and an azimuth range of about 100 degrees. In addition to this large-scale deployment, we set out 7 beamforming arrays approximately collocated with iMUSH broadband seismographs, and above clusters of seismicity in the region. The aperture of these arrays was about 1 km with an instrument spacing of 100 m. The final deployment ended only days before the AGU abstract deadline, so we have not yet examined all of the data. However, the preliminary indications are that signal to noise is excellent: The shots, several of which registered on PNSN as ML>2.1, carried across the entire array, and were recorded as far away as Seattle and Corvallis on permanent stations. The array also recorded a

  17. Seismic anisotropy inferred from teleseismic and local shear waves beneath the Pamir

    NASA Astrophysics Data System (ADS)

    Eken, Tuna; Kufner, Sofia-Katerina; Tilmann, Frederik; Schurr, Bernd; Yuan, Xiaohui; Mechie, James; Haberland, Christian; Kind, Rainer

    2014-05-01

    The Pamir region, which is located at the north of the western Himalayan syntaxis, is considered to be a unique place with its active continental subduction. Strongly arcuate southward-directed subduction of Eurasian continental lithosphere is evident in the high resolution images inferred from P receiver function (PRF) analysis and precise hypocenter distributions of Pamir deep seismicity reaching intermediate depths (up to 300 km depth). Our main motivation in the current study is to map lateral variations of seismic anisotropy parameters for a better understanding of a possible link between surface and internal deformation in the context of crust and mantle structure. To achieve this aim we perform shear wave splitting (SWS) analysis on both S-wave signals of local deep-focused earthquakes and SKS phases of teleseismic earthquakes recorded at several temporary passive seismic networks (i.e., TIPAGE, FERGANA, TIPTIMON) in the region. Our first findings inferred from SKS splitting analysis involve 460 measurements obtained for 71 high quality teleseismic events (Mw>5.8) recorded at 48 broadband stations within the TIPAGE seismic network with delay times of typically 1-1.5 s. The pattern of fast polarization directions (FPDs) measured at the stations in the central Pamir, overlying the zone of intermediate depth seismicity mainly follows the rotation of the strike direction of the subduction except that stations in the east differ by up to ~10° in an anti-clockwise direction. The FPDs in this part show nearly NE-SW directions in the west and toward the east exhibit a gradual clockwise rotation with ENE-WSW orientations along most of the main profile. Similarly the stations located in the vicinity of the Main Pamir Thrust in the north indicate FPDs which tend to align with prominent southward dipping thrust faults ~ 150 km to the north or northwest of the deep seismicity as well as the main strike of the Alai Valley. Our initial findings imply that the subduction

  18. The multiparameter station at Galeras Volcano (Colombia): concept and realization

    NASA Astrophysics Data System (ADS)

    Seidl, Dieter; Hellweg, Margaret; Calvache, Marta; Gomez, Diego; Ortega, Adriana; Torres, Roberto; Böker, Franz; Buttkus, Burkhard; Faber, Eckhard; Greinwald, Siegfried

    2003-07-01

    Volcanoes are complex systems, in which the interaction of many different physical and chemical factors and processes contribute to changes in activity. In the past 40 years, our ability to observe and quantify short-term changes in a volcano's activity has improved due to the installation of seismometers and tiltmeters and the continuous records they provide. However, due to instrumental limitations, the observations have mainly been used phenomenologically, to draw inferences about possible changes on the basis of previous experience. Since 1995, the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) and the Instituto de Investigación e Información Geocientı´fica, Minero-Ambiental y Nuclear (INGEOMINAS) have been working to develop and deploy a multiparameter (MP) station on Galeras Volcano, Colombia. This station is designed to concurrently measure various geophysical and geochemical parameters. It includes three broadband seismometers at the crater rim, as well as a more remotely located, broadband seismic reference. At other locations in the crater or on the rim, electromagnetic probes, an infrasound sensor and a weather station are operating. The data from these sensors are digitized at each site with 24-bit digitizers and transmitted by spread-spectrum radio, via repeater when necessary, to the Observatorio Vulcanológico y Sismológico (OVP) in the city of Pasto. There they are received and displayed on a networked personal computer and recorded continuously. The data flow into the routine analysis procedures of the OVP and the continuous data are archived on CD. In addition to the other sensors, a system of specially developed sensors continuously monitors the chemistry and physics of the gases at fumaroles on the active cone. The data from this system are also transmitted in realtime to OVP and recorded. The continuous recordings of the MP station are supplemented by regular thermographic measurements of the surface temperature in the crater

  19. Martian seismicity

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.; Grimm, Robert E.

    1991-01-01

    The design and ultimate success of network seismology experiments on Mars depends on the present level of Martian seismicity. Volcanic and tectonic landforms observed from imaging experiments show that Mars must have been a seismically active planet in the past and there is no reason to discount the notion that Mars is seismically active today but at a lower level of activity. Models are explored for present day Mars seismicity. Depending on the sensitivity and geometry of a seismic network and the attenuation and scattering properties of the interior, it appears that a reasonable number of Martian seismic events would be detected over the period of a decade. The thermoelastic cooling mechanism as estimated is surely a lower bound, and a more refined estimate would take into account specifically the regional cooling of Tharsis and lead to a higher frequency of seismic events.

  20. Earthquake location determination using data from DOMERAPI and BMKG seismic networks: A preliminary result of DOMERAPI project

    SciTech Connect

    Ramdhan, Mohamad; Nugraha, Andri Dian; Widiyantoro, Sri; Métaxian, Jean-Philippe; Valencia, Ayunda Aulia

    2015-04-24

    DOMERAPI project has been conducted to comprehensively study the internal structure of Merapi volcano, especially about deep structural features beneath the volcano. DOMERAPI earthquake monitoring network consists of 46 broad-band seismometers installed around the Merapi volcano. Earthquake hypocenter determination is a very important step for further studies, such as hypocenter relocation and seismic tomographic imaging. Ray paths from earthquake events occurring outside the Merapi region can be utilized to delineate the deep magma structure. Earthquakes occurring outside the DOMERAPI seismic network will produce an azimuthal gap greater than 180{sup 0}. Owing to this situation the stations from BMKG seismic network can be used jointly to minimize the azimuthal gap. We identified earthquake events manually and carefully, and then picked arrival times of P and S waves. The data from the DOMERAPI seismic network were combined with the BMKG data catalogue to determine earthquake events outside the Merapi region. For future work, we will also use the BPPTKG (Center for Research and Development of Geological Disaster Technology) data catalogue in order to study shallow structures beneath the Merapi volcano. The application of all data catalogues will provide good information as input for further advanced studies and volcano hazards mitigation.

  1. Three-dimensional seismic velocity structure and earthquake relocations at Katmai, Alaska

    NASA Astrophysics Data System (ADS)

    Murphy, Rachel; Thurber, Clifford; Prejean, Stephanie; Bennington, Ninfa

    2014-04-01

    We invert arrival time data from local earthquakes occurring between September 2004 and May 2009 to determine the three-dimensional (3D) upper crustal seismic structure in the Katmai volcanic region. Waveforms for the study come from the Alaska Volcano Observatory's permanent network of 20 seismic stations in the area (predominantly single-component, short period instruments) plus a densely spaced temporary array of 11 broadband, 3-component stations. The absolute and relative arrival times are used in a double-difference seismic tomography inversion to solve for 3D P- and S-wave velocity models for an area encompassing the main volcanic centers. The relocated hypocenters provide insight into the geometry of seismogenic structures in the area, revealing clustering of events into four distinct zones associated with Martin, Mageik, Trident-Novarupta, and Mount Katmai. The seismic activity extends from about sea level to 2 km depth (all depths referenced to mean sea level) beneath Martin, is concentrated near 2 km depth beneath Mageik, and lies mainly between 2 and 4 km depth below Katmai and Trident-Novarupta. Many new features are apparent within these earthquake clusters. In particular, linear features are visible within all clusters, some associated with swarm activity, including an observation of earthquake migration near Trident in 2008. The final velocity model reveals a possible zone of magma storage beneath Mageik, but there is no clear evidence for magma beneath the Katmai-Novarupta area where the 1912 eruptive activity occurred, suggesting that the storage zone for that eruption may have largely been evacuated, or remnant magma has solidified.

  2. Three-dimensional seismic velocity structure and earthquake relocations at Katmai, Alaska

    USGS Publications Warehouse

    Murphy, Rachel; Thurber, Clifford; Prejean, Stephanie G.; Bennington, Ninfa

    2014-01-01

    We invert arrival time data from local earthquakes occurring between September 2004 and May 2009 to determine the three-dimensional (3D) upper crustal seismic structure in the Katmai volcanic region. Waveforms for the study come from the Alaska Volcano Observatory's permanent network of 20 seismic stations in the area (predominantly single-component, short period instruments) plus a densely spaced temporary array of 11 broadband, 3-component stations. The absolute and relative arrival times are used in a double-difference seismic tomography inversion to solve for 3D P- and S-wave velocity models for an area encompassing the main volcanic centers. The relocated hypocenters provide insight into the geometry of seismogenic structures in the area, revealing clustering of events into four distinct zones associated with Martin, Mageik, Trident-Novarupta, and Mount Katmai. The seismic activity extends from about sea level to 2 km depth (all depths referenced to mean sea level) beneath Martin, is concentrated near 2 km depth beneath Mageik, and lies mainly between 2 and 4 km depth below Katmai and Trident-Novarupta. Many new features are apparent within these earthquake clusters. In particular, linear features are visible within all clusters, some associated with swarm activity, including an observation of earthquake migration near Trident in 2008. The final velocity model reveals a possible zone of magma storage beneath Mageik, but there is no clear evidence for magma beneath the Katmai-Novarupta area where the 1912 eruptive activity occurred, suggesting that the storage zone for that eruption may have largely been evacuated, or remnant magma has solidified.

  3. Deformation of the Continental Lithosphere at the Margins of the North American Craton: Constraints from Seismic Anisotropy

    NASA Astrophysics Data System (ADS)

    Long, M. D.; Benoit, M. H.; Ford, H. A.; Wirth, E. A.; Aragon, J. C.; Abrahams, L.; McNamara, J.; Jackson, K.

    2015-12-01

    Earth's continents exhibit striking properties, including relatively thick and low-density crust and a strong, thick, long-lived mantle lithosphere. Major questions related to the formation, stability, evolution, and dynamics of cratonic lithosphere remain unanswered. One promising avenue for understanding the stability of cratonic lithosphere through geologic time is to understand how their margins are deformed via tectonic processes such as orogenesis and rifting. Here we present results of several recent and ongoing studies which aim to constrain past lithospheric deformation along the eastern margin of the North American craton. Each of these studies focuses on constraining seismic anisotropy, or the directional dependence of seismic wavespeeds, in the lithospheric upper mantle. Because there is a causative link between upper mantle deformation and the resulting seismic anisotropy, studies of anisotropic structure in the upper mantle beneath continental interiors can shed light on the deformation processes associated with past tectonic events. The recent explosion in the availability of seismic data in the eastern United States, largely due to the EarthScope initiative, has enabled detailed studies of lithospheric deformation using anisotropic receiver function (RF) analysis and SKS splitting analysis. A comparison of lithospheric structure inferred from RFs for stations located to the east of the Grenville deformation front with those located within the cratonic interior argues for extensive deformation of the lithosphere during the formation and/or breakup of Rodinia. The pattern of fast SKS splitting directions measured at USArray Transportable Array (TA) stations shows clear evidence for a specific lithospheric anisotropy signature at stations beneath the Appalachian Mountains, indicating strong, coherent lithospheric deformation associated with Appalachian orogenesis. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment, a linear array

  4. Observed inflation-deflation cycles at Popocatepetl volcano using tiltmeters and its possible correlation with regional seismic activity in Mexico

    NASA Astrophysics Data System (ADS)

    Contreras Ruiz Esparza, M. G., Sr.; Jimenez Velazquez, J. C., Sr.; Valdes Gonzalez, C. M., Sr.; Reyes Pimentel, T. A.; Galaviz Alonso, S. A.

    2014-12-01

    Popocatepetl, the smoking mountain, is a stratovolcano located in central Mexico with an elevation of 5450 masl. The active volcano, close to some of the largest urban centers in Mexico - 60 km and 30 km far from Mexico City and Puebla, respectively - poses a high hazard to an estimated population of 500 thousand people living in the vicinity of the edifice. Accordingly, in July 1994 the Popocatepetl Volcanological Observatory (POVO) was established. The observatory is operated and supported by the National Center for Disaster Prevention of Mexico (CENAPRED), and is equipped to fully monitor different aspects of the volcanic activity. Among the instruments deployed, we use in this investigation two tiltmometers and broad-band seismometers at two sites (Chipiquixtle and Encinos), which send the information gathered continuously to Mexico City.In this research, we study the characteristics of the tiltmeters signals minutes after the occurrence of certain earthquakes. The Popocatepetl volcano starts inflation-deflation cycles due to the ground motion generated by events located at certain regions. We present the analysis of the tiltmeters and seismic signals of all the earthquakes (Mw>5) occurred from January 2013 to June 2014, recorded at Chipiquixtle and Encinos stations. First, we measured the maximum tilt variation after each earthquake. Next, we apply a band-pass filter for different frequency ranges to the seismic signals of the two seismic stations, and estimated the total energy of the strong motion phase of the seismic record. Finally, we compared both measurements and observed that the maximum tilt variations were occurring when the maximum total energy of the seismic signals were in a specific frequency range. We also observed that the earthquake records that have the maximum total energy in that frequency range were the ones with a epicentral location south-east of the volcano. We conclude that our observations can be used set the ground for an early

  5. Analysis of the 23 June 2001 Southern Peru Earthquake Using Locally Recorded Seismic Data

    NASA Astrophysics Data System (ADS)

    Tavera, H.; Comte, D.; Boroschek, R.; Dorbath, L.; Portugal, D.; Haessler, H.; Montes, H.; Bernal, I.; Antayhua, Y.; Salas, H.; Inza, A.; Rodriguez, S.; Glass, B.; Correa, E.; Balmaceda, I.; Meneses, C.

    2001-12-01

    The 23 June 2001, Mw=8.4 southern Peru earthquake ruptured the northern and central part of the previous large earthquake occurred on 13 August 1868, Mw ~9. A detailed analysis of the aftershock sequence was possible due to the deployment of a temporary seismic network along the coast in the Arequipa and Moquegua districts, complementing the Peruvian permanent stations. The deployed temporary network included 10 short period three component stations from the U. of Chile-IRD-France and 7 broad-band seismic stations from the Instituto Geofísico del Perú. This network operated during the first weeks after the mainshock and recorded the major aftershocks like the larger one occurred on 7 July 2001, Mw=7.5, this event defines the southern limit of the rupture area of the 2001 Peruvian earthquake. The majority of the aftershocks shows a thrusting fault focal mechanisms according with the average convergence direction of the subducting Nazca plate, however, normal faulting events are also present in the aftershock sequence like the 5 July 2001, Mw=6.6 one. The depth distribution of the events permitted a detailed definition of the Wadati-Benioff zone in the region. The segment between Ilo and Tacna did not participated in the rupture process of the 2001 southern Peru earthquake. Seismicity located near the political Peruvian-Chilean boundary was reliable determined using the data recorded by the northern Chile permanent network. Analysis of the mainshock and aftershock acelerograms recorded in Arica, northern Chile are also included. The occurrence of the 1995 Antofagasta (Mw=8.0) and the 2001 southern Peru earthquakes suggests that the probability of having a major earthquake in the northern Chile region increased, considering that the previous large earthquake in this region happened in 1877 (Mw ~9), and since that time no earthquake with magnitude Mw>8 had occurred inside of the 1877 estimated rupture area (between Arica and Antofagasta).

  6. Understanding Extension Within a Convergent Orogen: Initial Results From the Carpathian Basins Seismic Project

    NASA Astrophysics Data System (ADS)

    Stuart, G. W.; Houseman, G.; Dando, B.; Hegedus, E.; Brueckl, E.; Radovanovic, S.; Falus, G.; Kovacs, A.; Hausmann, H.; Brisbourne, A.

    2007-12-01

    The Carpathian Basins Project (CBP) aims to understand the origin of Miocene-age extensional basins, of which the Pannonian Basin is the largest, within the arc of the Alpine-Carpathian Mountain Ranges - a compressional structure. Analysis of the subsidence history of the Pannonian Basin shows that its mantle lithosphere has undergone a much greater degree of extension than the overlying crust. We describe the results of a temporary seismic deployment to test competing theories of how the continental lithosphere evolved in the region. We deployed a 46-element seismic network, 450 km x 80 km, oriented in a NW-SE direction, crossing the Vienna and western Pannonian Basins in Austria, Hungary and Serbia. The network ran for 14 months from early May 2006. The stations were broadband to 30s and spaced at ~30 km along 3 parallel lines, which are 40 km apart. The principal object of this network is to use P and S-wave teleseismic tomography to image the upper mantle. P- wave residuals from sources perpendicular to the tectonic grain show a ~1s variation across the Mid-Hungarian High in to the Pannonian Basin. This delay cannot be explained by sedimentary or crustal thickness variations, which are well-controlled by boreholes, deep seismic soundings and our own receiver function analyses. We must infer significant lithospheric thinning and anomalously low asthenospheric velocities underlying the Pannonian Basin to explain our observations. These travel time delays are accompanied by a dramatic change in the orientation of SKS splitting measurements from E-W to NW-SE across the Mid-Hungarian High. We have also installed a more broadly distributed regional broadband array of 10 instruments (broadband to 120 sec) for 2 years from September 2005, spaced at ~100km within Hungary, Croatia and Serbia to augment the data available from permanent broadband networks in central Europe. Preliminary interstation surface wave dispersion results from across the Pannonian Basin imply

  7. Deep structure of Llaima Volcano from seismic ambient noise tomography: Preliminary results

    NASA Astrophysics Data System (ADS)

    Franco, L.; Mikesell, T. D.; Rodd, R.; Lees, J. M.; Johnson, J. B.; Ronan, T.

    2015-12-01

    The ambient seismic noise tomography (ANT) method has become an important tool to image crustal structures and magmatic bodies at volcanoes. The frequency band of ambient noise provides complimentary data and added resolution to the deeper volcanic structures when compared to traditional tomography based on local earthquakes. The Llaima Volcano (38° 41.9' S and 71° 43.8' W) is a stratovolcano of basaltic-andesitic composition. Llaima is located in the South Volcanic Zone (ZVS) of the Andes and is listed as one of the most active volcanoes in South America, with a long documented historical record dating back to 1640. Llaima experienced violent eruptions in 1927 and 1957 (Naranjo and Moreno, 1991), and its last eruptive cycle (2008-2010) is considered the most important after the 1957 eruption. Lacking seismic constraints on the deep structure under Llaima, petrologic data have suggested the presence of magmatic bodies (dikes). These bodies likely play an important role in the eruptive dynamics of Llaima (Bouvet de Maisonneuve, C., et al 2012). Analysis of the 2008-2010 seismicity shows a southern zone (approx. 15 km from the Llaima summit) where there were many Very Long Period events occurring prior to the eruptions. This is in agreement with a deformation zone determined by InSAR analysis (Fournier et al, 2010 and Bathke, 2011), but no geologic model based on geophysical imaging has been created yet. Beginning in 2009, staff from the Chilean Geological Survey (SERNAGEOMIN) started to install a permanent seismic network consisting of nine stations. These nine stations have allowed Chilean seismologists to closely monitor the activity at Llaima, but prevented a high-resolution tomographic imaging study. During the summer of 2015, a temporary seismic network consisting of 26 stations was installed around Llaima. In the work presented here, we analyze continuous waveforms recorded between January and April 2015 from a total of 35 broadband stations (permanent and

  8. Seismicity and Fault Zone Structure Near the Xinfengjiang Water Reservoir, Guangdong, China

    NASA Astrophysics Data System (ADS)

    Yang, H.; Sun, X.; He, L.; Wang, S.

    2015-12-01

    Xingfengjiang Water Reservoir (XWR) was built in 1958 and the first impoundment was conducted in 1959. Immediately following the reservoir impoundment, a series of earthquakes occurred in the vicinity of the XWR, including the 1962 M6.1 earthquake that occurred ~1 km next to the dam. Numerous small earthquakes take place in this region presently, making it one of the most active seismic zones in Guangdong. To investigate the present seismicity and associated fault zone structure, we deployed a temporary seismic network, including a dense linear array across the Ren-Zi-Shi fault southwest to the reservoir. The temporary network is consisted of 42 stations that are operated in the field for more than one month. Because of the mountainous terrain, it is impossible to deploy broadband sensors. Here we use DDV-5 seismometer with a central frequency of 120Hz-5s that is independent on external GPS and battery. During our deployment, numerous earthquakes were recorded. Preliminary results of travel time analysis have shown the characteristic of low velocity fault zone. More detailed analysis, including relocation of earthquakes, ambient noise cross correlation, and modeling body waves, will be presented.

  9. Characterization of tsunamigenic earthquake in Java region based on seismic wave calculation

    SciTech Connect

    Pribadi, Sugeng; Afnimar,; Puspito, Nanang T.; Ibrahim, Gunawan

    2014-03-24

    This study is to characterize the source mechanism of tsunamigenic earthquake based on seismic wave calculation. The source parameter used are the ratio (Θ) between the radiated seismic energy (E) and seismic moment (M{sub o}), moment magnitude (M{sub W}), rupture duration (T{sub o}) and focal mechanism. These determine the types of tsunamigenic earthquake and tsunami earthquake. We calculate the formula using the teleseismic wave signal processing with the initial phase of P wave with bandpass filter 0.001 Hz to 5 Hz. The amount of station is 84 broadband seismometer with far distance of 30° to 90°. The 2 June 1994 Banyuwangi earthquake with M{sub W}=7.8 and the 17 July 2006 Pangandaran earthquake with M{sub W}=7.7 include the criteria as a tsunami earthquake which distributed about ratio Θ=−6.1, long rupture duration To>100 s and high tsunami H>7 m. The 2 September 2009 Tasikmalaya earthquake with M{sub W}=7.2, Θ=−5.1 and To=27 s which characterized as a small tsunamigenic earthquake.

  10. Seismic structure and origin of active intraplate volcanoes in Northeast Asia

    NASA Astrophysics Data System (ADS)

    Duan, Yonghong; Zhao, Dapeng; Zhang, Xiankang; Xia, Shaohong; Liu, Zhi; Wang, Fuyun; Li, Li

    2009-05-01

    Three-dimensional P-wave velocity structure beneath the Changbai and other intraplate volcanic areas in Northeast Asia is determined by inverting 1378 high-quality P-wave arrival times from 186 teleseismic events recorded by 61 broadband seismic stations. Low-velocity (low-V) anomalies are revealed beneath the Changbai, Longgan, Xianjindao volcanoes. High-velocity (high-V) anomalies are found in the mantle transition zone, where deep-focus earthquakes under Hunchun occur at depths of 500-600 km. The high-V anomaly reflects the deep subduction of the Pacific slab under NE Asia which may have contributed to the formation of the Changbai, Longgang, Xianjindao and Jingpohu intraplate volcanoes. A low-V anomaly is also revealed in the mantle transition zone, which may have a close relationship with the occurrence of deep earthquakes under the Hunchun area. Our results support the Big Mantle Wedge (BMW) model by Zhao et al. [Zhao, D., Lei, J., Tang, Y., 2004. Origin of the Changbai volcano in northeast China: evidence from seismic tomography, Chin. Sci. Bull. 49, 1401-1408; Zhao, D., Maruyama, S., Omori, S., 2007. Mantle dynamics of western Pacific and East Asia: insight from seismic tomography and mineral physics. Gondwana Res. 11, 120-131.] who proposed that the intraplate volcanoes in NE Asia are caused by the back-arc magmatism associated with the deep dehydration process of the subducting slab and convective circulation process in the BMW above the stagnant Pacific slab.

  11. Seismicity in Northern Germany

    NASA Astrophysics Data System (ADS)

    Bischoff, Monika; Gestermann, Nicolai; Plenefisch, Thomas; Bönnemann, Christian

    2013-04-01

    Northern Germany is a region of low tectonic activity, where only few and low-magnitude earthquakes occur. The driving tectonic processes are not well-understood up to now. In addition, seismic events during the last decade concentrated at the borders of the natural gas fields. The source depths of these events are shallow and in the depth range of the gas reservoirs. Based on these observations a causal relationship between seismicity near gas fields and the gas production is likely. The strongest of these earthquake had a magnitude of 4.5 and occurred near Rotenburg in 2004. Also smaller seismic events were considerably felt by the public and stimulated the discussion on the underlying processes. The latest seismic event occurred near Langwedel on 22nd November 2012 and had a magnitude of 2.8. Understanding the causes of the seismicity in Northern Germany is crucial for a thorough evaluation. Therefore the Seismological Service of Lower Saxony (NED) was established at the State Office for Mining, Energy and Geology (LBEG) of Lower Saxony in January 2013. Its main task is the monitoring and evaluation of the seismicity in Lower Saxony and adjacent areas. Scientific and technical questions are addressed in close cooperation with the Seismological Central Observatory (SZO) at the Federal Institute for Geosciences and Natural Resources (BGR). The seismological situation of Northern Germany will be presented. Possible causes of seismicity are introduced. Rare seismic events at greater depths are distributed over the whole region and probably are purely tectonic whereas events in the vicinity of natural gas fields are probably related to gas production. Improving the detection threshold of seismic events in Northern Germany is necessary for providing a better statistical basis for further analyses answering these questions. As a first step the existing seismic network will be densified over the next few years. The first borehole station was installed near Rethem by BGR

  12. Calibration of 3D Upper Mantle Structure in Eurasia Using Regional and Teleseismic Full Waveform Seismic Data

    SciTech Connect

    Barbara Romanowicz; Mark Panning

    2005-04-23

    Adequate path calibrations are crucial for improving the accuracy of seismic event location and origin time, size, and mechanism, as required for CTBT monitoring. There is considerable information on structure in broadband seismograms that is currently not fully utilized. The limitations have been largely theoretical. the development and application to solid earth problems of powerful numerical techniques, such as the Spectral Element Method (SEM), has opened a new era, and theoretically, it should be possible to compute the complete predicted wavefield accurately without any restrictions on the strength or spatial extent of heterogeneity. This approach requires considerable computational power, which is currently not fully reachable in practice. We propose an approach which relies on a cascade of increasingly accurate theoretical approximations for the computation of the seismic wavefield to develop a model of regional structure for the area of Eurasia located between longitudes of 30 and 150 degrees E, and latitudes of -10 to 60 degrees North. The selected area is particularly suitable for the purpose of this experiment, as it is highly heterogeneous, presenting a challenge for calibration purposes, but it is well surrounded by earthquake sources and, even though they are sparsely distributed, a significant number of high quality broadband digital stations exist, for which data are readily accessible through IRIS (Incorporated Research Institutions for Seismology) and the FDSN (Federation of Digital Seismic Networks). The starting models used will be a combination of a-priori 3D models recently developed for this region, combining various geophysical and seismological data, and a major goal of this study will be to refine these models so as to fit a variety of seismic waveforms and phases.

  13. PQLX: A seismic data quality control system description, applications, and users manual

    USGS Publications Warehouse

    McNamara, Daniel E.; Boaz, Richard I.

    2011-01-01

    We present a detailed description and users manual for a new tool to evaluate seismic station performance and characteristics by providing quick and easy transitions between visualizations of the frequency and time domains. The software is based on the probability density functions (PDF) of power spectral densities (PSD) (McNamara and Buland, 2004) and builds on the original development of the PDF stand-alone software system (McNamara and Boaz, 2005) and the seismological data viewer application PQL (IRIS-PASSCAL Quick Look) and PQLII (available through the IRIS PASSCAL program: http://www.passcal.nmt.edu/content/pql-ii-program-viewing-data). With PQLX (PQL eXtended), computed PSDs are stored in a MySQL database, allowing a user to access specific time periods of PSDs (PDF subsets) and time series segments through a GUI-driven interface. The power of the method and software lies in the fact that there is no need to screen the data for system transients, earthquakes, or general data artifacts, because they map into a background probability level. In fact, examination of artifacts related to station operation and episodic cultural noise allow us to estimate both the overall station quality and a baseline level of Earth noise at each site. The output of this analysis tool is useful for both operational and scientific applications. Operationally, it is useful for characterizing the current and past performance of existing broadband stations, for conducting tests on potential new seismic station locations, for evaluating station baseline noise levels (McNamara and others, 2009), for detecting problems with the recording system or sensors, and for evaluating the overall quality of data and metadata. Scientifically, the tool allows for mining of PSDs for investigations on the evolution of seismic noise (for example, Aster and others, 2008; and Aster and others, 2010) and other phenomena. Currently, PQLX is operational at several organizations including the USGS National

  14. Modeling regional seismic waves. Final report, 26 September 1991-25 September 1992

    SciTech Connect

    Helmberger, D.V.; Harkrider, D.G.

    1992-03-24

    This research can be divided into two main topics: using the moment of regional Rayleigh waves and a regional magnitude based on the maximum amplitude of the shear wave train as a seismic discriminant and source retrieval from broadband regional seismograms. In section 1, we propose using the ratio of M sub L (local magnitude) to M sub O (Scalar Seismic Moment) as a regional discriminant analagous to the teleseismic discriminant using the m sub b; M sub s ratio. We applied this criterion to a data set of 299 earthquakes and 178 explosions and found that this ratio appears to be diagnostic of source type. This method does require the determination of regional crustal models and path calibrations from master events or by other means. In section 2, we develop and test a method of relocation and source characterization of small earthquakes using one modern regional station. First we model teleseismic body-waves of two events, which are used as masters. Short period depth phases, pP and sP, are used to establish the epicentral depth, and the events are relocated using calibrated stations and a mantle model derived for this region, TIP. The events moved upward by 12 and 31 kms, respectively. Secondly, these events can be used as masters in the calibration of other systems, case-based event characterizations, etc.

  15. Surface-wave Tomography of East African Rift System using Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Kim, S.; Kang, T.; Baag, C.; Nyblade, A. A.

    2008-12-01

    The surface-wave tomography technique for the ambient seismic noise is applied to the east African rift system to investigate shallow crustal structures of the region. Even if the technique has been widely used in many regions to investigate crustal structure in the world, there have been difficulties in application of the technique to the east African region because of unstable data conditions of PASSCAL experiments. A meticulous check of record by record enables us of applying the technique to understand the tectonic environment of the region. The long-period data of one month showing good quality in cross-correlation results are used in this study. They are from the 1994-95 Tanzania Passive-Source Seismic Experiment for the Tanzania craton and its surrounding rift zone, and from the 2000-02 Ethiopia/Kenya Broadband Seismic Experiment and the adjacent permanent stations of the African Array for the Ethiopia rift. The Rayleigh- and Love-wave group-speed maps were inverted using LSQR algorithm for several period bands (5 - 50 s). The preliminary group-speed distribution maps yield results roughly consistent with regional geology. The tomographic images of the Tanzania region show a strong high velocity anomaly at the location corresponding to the Tanzania craton and low velocity anomalies at the surrounding rift regions. For the Ethiopia regions, the features of low velocity anomalies roughly agree with the Tertiary volcanic regions. Combining the Tanzania and Ethiopia broadband arrays, the outline of the east African rift system can be identified as the low velocity anomalies in the surface-wave tomographic results. The structural variation with depth and the feature of the regional shear-wave anisotropy of crust will be explored by converting group- speed dispersion curves into shear-wave velocity structure.

  16. The ADN project : an integrated seismic monitoring of the northern Ecuadorian subduction

    NASA Astrophysics Data System (ADS)

    Nocquet, Jean-Mathieu; Yepes, Hugo; Vallee, Martin; Mothes, Patricia; Regnier, Marc; Segovia, Monica; Font, Yvonne; Vaca, Sandro; Bethoux, Nicole; Ramos, Cristina

    2010-05-01

    The subduction of the Nazca plate beneath South America has caused one of the largest megathrust earthquake sequence during the XXth century with three M>7.7 earthquakes that followed the great 1906 (Mw = 8.8) event. Better understanding the processes leading to the occurrence of large subduction earthquakes requires to monitor the ground motion over a large range of frequencies. We present a new network (ADN) developed under a collaboration between the IRD-GeoAzur (Nice, France) and the IG-EPN (Quito, Ecuador). Each station of the ADN network includes a GPS recording at 5 Hz, an accelerometer and a broadband seismometer. CGPS data will quantify the secular deformation induced by elastic locking along the subduction interface, enabling a detailed modelling of the coupling distribution. CGPS will be used to monitor any transient deformation induced by Episodic Slip Event along the subduction, together with broadband seismometers that can detect any tremors or seismic signatures that may accompany them. In case of any significant earthquake, 5 Hz GPS and accelerometer will provide near field data for earthquake source detailed study. Finally, the broadband seismometers will be used for study of the microseismicity and structure of the subduction zone. The network includes 9 stations, operating since 2008 and covering the coastal area from latitude 1.5°S to the Colombian border. In this poster, we will present preliminary assessment of the data, first hypocenters location, magnitude and focal mechanism determination, as well as results about an episodic slip event detected in winter 2008.

  17. Broadband multimedia for education.

    PubMed

    Mackinnon, M

    1998-01-01

    Over the next five to ten years the accelerating development of computing and broadband networks will lead to a revolution in the ways in which health care is delivered. Patients will spend less time in the great institutions of the tertiary hospitals and the illnesses taking them there will assume a different pattern. The new information technologies will foster the emergence of general practices with a new emphasis on keeping patients in their communities for medical management. Knowledge exchange and delivery--to both patient and practitioner--will therefore become an increasingly important component of the health-care system in the next millennium.

  18. Ambient seismic noise tomography of Jeju Island, South Korea

    NASA Astrophysics Data System (ADS)

    Lee, S. J.; Rhie, J.; Kim, S.; Kang, T. S.; Kim, Y.

    2015-12-01

    Jeju Island, formed by Cenozoic basaltic eruptions, is an island off the southern coast of the Korean Peninsula. This volcanic island is far from the plate boundaries and the fundamental cause of the volcanic activity in this region is not understood well. To understand the origin of the island, resolving the detailed seismic velocity structures is crucial. Therefore, we applied ambient noise tomography to study the velocity structures of the island. Continuous waveform data recorded at 20 temporary and 3 permanent broad-band seismic stations are used. The group and phase velocity dispersion curves of the fundamental mode Rayleigh waves are extracted from cross-correlograms for 253 station pairs by adopting multiple filter technique. The fast marching method and the subspace method are jointly applied to construct 2-D group and phase velocity maps for periods ranging between 1 and 15 s. 1-D shear wave velocity models and their uncertainties are estimated by the Bayesian technique. The optimal number of the layers are determined at the end of the burn-in period based on the Bayesian Information Criteria (BIC). Final 3-D velocity model of the island is constructed by compiling 1-D models. In our 3-D model, a distinct low velocity anomaly appears beneath Mt. Halla from surface to about 6 km depth. The surficial extent of the anomaly is more or less consistent with the surface geologic feature of the third-stage basaltic eruption reported by previous studies but the vertical extension of the anomaly is not well constrained. To improve the velocity model, especially enhance the vertical resolution of the anomaly, we will apply joint analysis of the surface wave dispersions and teleseismic receiver functions. The improved model will provide more information to infer the tectonic or volcanic implications of the anomaly and unravel the origin of the strange volcanic island in South Korea.

  19. Wavelet-based coherence measures of global seismic noise properties

    NASA Astrophysics Data System (ADS)

    Lyubushin, A. A.

    2015-04-01

    The coherent behavior of four parameters characterizing the global field of low-frequency (periods from 2 to 500 min) seismic noise is studied. These parameters include generalized Hurst exponent, multifractal singularity spectrum support width, the normalized entropy of variance, and kurtosis. The analysis is based on the data from 229 broadband stations of GSN, GEOSCOPE, and GEOFON networks for a 17-year period from the beginning of 1997 to the end of 2013. The entire set of stations is subdivided into eight groups, which, taken together, provide full coverage of the Earth. The daily median values of the studied noise parameters are calculated in each group. This procedure yields four 8-dimensional time series with a time step of 1 day with a length of 6209 samples in each scalar component. For each of the four 8-dimensional time series, a multiple correlation measure is estimated, which is based on computing robust canonical correlations for the Haar wavelet coefficients at the first detail level within a moving time window of the length 365 days. These correlation measures for each noise property demonstrate essential increasing starting from 2007 to 2008 which was continued till the end of 2013. Taking into account a well-known phenomenon of noise correlation increasing before catastrophes, this increasing of seismic noise synchronization is interpreted as indicators of the strongest (magnitudes not less than 8.5) earthquakes activation which is observed starting from the Sumatra mega-earthquake of 26 Dec 2004. This synchronization continues growing up to the end of the studied period (2013), which can be interpreted as a probable precursor of the further increase in the intensity of the strongest earthquakes all over the world.

  20. Preliminary results from a new large-aperture seismic and GPS array in southern Mexico

    NASA Astrophysics Data System (ADS)

    Cabral-Cano, E.; Demets, C.; Brudzinski, M.; Arciniega-Ceballos, A.; Diaz-Molina, O.; Correa-Mora, F.

    2006-12-01

    A multi-year deployment of a large aperture seismic and GPS array in southern Mexico, for the purpose of studying the Oaxaca segment of the Middle America subduction zone, entered its second development phase during the summer of 2006. The Oaxaca segment is one of the few places on earth where land-based geophysical observations can be used to study both the locked, seismogenic area of a subduction interface and region of deeper transitional slip, where episodic tremor and slip may originate. The newly expanded array, consisting of eight broad-band seismic and nine continuous GPS stations, measures deformation in the state of Oaxaca and adjacent areas. Important goals of the deployment are to better understand the spatial and temporal histories of episodic slip transients, and their role in either relieving or increasing strain accumulating along the seismogenic portion of a subduction interface. The combined GPS and seismic arrays will be a powerful tool for studying slow slip and non-volcanic tremor, as well as imaging spatial and temporal variations in frictional coupling along the locked and transitional zones beneath our network. Preliminary analysis of seismic data indicates that the seismic stations are uniformly characterized by low noise in the non-volcanic tremor passband of 1-5 Hz, accomplishing an important goal of our site selection. We attribute this to our use of a newly developed, on-site 'listening test' in which our seismic equipment was used to record 30-60 minutes of data before the vault was excavated at a potentially low noise site. The data were processed on site with newly developed software to determine whether the amplitude of the background noise within the frequency band of non-volcanic tremors was low enough to observe the amplitude of tremors previously recorded in Cascadia. Using this test, we confirmed in advance that our selected seismic sites had sufficiently low noise to observe non-volcanic tremor if it is similar to that in

  1. The Aysen (Southern Chile) 2007 Seismic Swarm: Volcanic or Tectonic Origin?

    NASA Astrophysics Data System (ADS)

    Comte, D.; Gallego, A.; Russo, R.; Mocanu, V.; Murdie, R.; Vandecar, J.

    2007-05-01

    The Aysen seismic swarm began January 23, 2007, with a magnitude 5.2 (USGS) earthquake and, after an apparent decrease in activity, continued with a magnitude 5.6 event on February 26. The swarm is characterized by numerous felt earthquakes of small to moderate magnitude, located at crustal depths beneath the Aysen Canal, a prominent fiord of the Chilean littoral. The region is characterized by the subduction of an active oceanic spreading ridge: the Chile Ridge, the divergent Nazca-Antarctic plate boundary, is currently subducting beneath continental South America along the Chile Trench at approximately 46.5°S, forming a plate triple junction in the vicinity of the Taitao Peninsula, somewhat south and west of the swarm. Also, the Liquine-Ofqui dextral strike- slip fault traverses the Aysen Canal in the vicinity of the swarm. This fault has been interpreted as a 1000 km long dextral intra-arc strike-slip fault zone, consisting of two major strands which extend north from the Chile Margin triple junction. The Liquiñe-Ofqui system is marked by several pull-apart basins along its trace through the area. Seismic activity along the Liquiñe-Ofqui fault zone has been poorly studied to date, largely because teleseismic events clearly related to the fault have been few, and southern hemisphere seismic stations are lacking. However, we deployed a dense temporary broad-band seismic network both onland and on the islands in the Aysen region, which allowed us to capture the initial phases of the swarm on some 20 stations, and to determine the background seismicity patterns in this area for the two years preceding the swarm. The swarm could be caused by several processes: the spatial and depth distribution of the events suggests that they are well correlated with reactivation of the southern end of the Liquiñe-Ofqui fault, as defined by geologic studies and onshore gravity data collected in southern Chile. The swarm may be related to formation of new volcanic center between

  2. Unusual Patterns of Seismicity during Eruptive and Non-eruptive Periods at the Persistently Restless Telica Volcano, Nicaragua

    NASA Astrophysics Data System (ADS)

    Rodgers, Melanie J.

    Telica Volcano, Nicaragua, is a persistently restless volcano with high rates of seismicity that can vary from less than ten events to over a thousand events per day. Low-frequency (LF) events dominate the seismic catalogue and seismicity rates at Telica show little clear correlation with periods of eruption. As such, traditional methods of forecasting of volcanic activity based on increases in seismicity and recognition of LF activity are not applicable. A single seismic station has been operating at Telica since 1993, and in 2010 we installed a broadband seismic and continuous GPS network (TESAND network) at Telica. In this study we investigate the seismic characteristics surrounding a nine-month period of phreatic to phreatomagmatic explosions in 1999, and also from the initial three-and-a-half year deployment of the TESAND network, including a three-month phreatic vulcanian eruptive period in 2011. We demonstrate that pertinent information can be obtained from analysis of single-station data, and while large seismic networks are preferable when possible, we note that for many volcanoes this is not possible. We find unusual patterns of seismicity before both eruptive periods; rather than a precursory increase in seismicity as is observed prior to many volcanic eruptions, we observe a decrease in seismicity many months prior to eruption. We developed a new program for cross-correlation of large seismic data catalogues and analysed multiplet activity surrounding both eruptive periods. We observed that the formation of new multiplets corresponds to periods of high event rates (during inter-eruptive periods) and high percentages of daily events that belong to a multiplet. We propose a model for the seismicity patterns observed at Telica, where changes in seismicity are related to a cyclic transition between open-system degassing and closed-system degassing. Periods of open-system degassing occur during non-eruptive episodes and are characterised by high event rates

  3. Investigations of Passive Seismic Body-Wave Interferometry Using Noise Auto-correlations for Crustal and Upper Mantle Structure

    NASA Astrophysics Data System (ADS)

    Oren, C.; Nowack, R. L.

    2015-12-01

    It is known that the positive lags of the auto-correlation for the seismic transmission response of a layered medium correspond to the reflection seismogram (Claerbout, 1968). In this study, we investigate the use of ambient seismic noise recorded at selected broadband USArray EarthScope Transportable Array (TA) stations to obtain effective reflection seismograms for frequencies up to 1 Hz. The goal is to determine the most suitable parameters used for the processing of ambient seismic noise for the identification of crustal and upper mantle reflections and to minimize unwanted artifacts in the noise correlations. In order to best retrieve the body-wave components of the Green's function beneath a station, a number of processing steps are required. We first remove the instrument response and apply a temporal normalization to remove the effects of the most energetic sources. Next we implement spectral whitening. We test several operators for the spectral whitening where the undulations of the power spectrum are related to the strengths of later arrivals in the auto-correlation. Different filters are then applied to the auto-correlation functions, including Gaussian and zero phase Butterworth filters, in order to reduce the effect of side lobes. Hourly auto-correlations are then stacked for up to one year. On the final stack, Automatic Gain Control (AGC) is applied to equalize the correlation amplitudes in the time domain. The robustness of the resulting ambient noise auto-correlation is first tested on selected TA stations in Nevada, where we are able to identify PmP and SmS a