Seismic Traces Calibration for CTBT
Development and Efficiency Analysis of Blast Techniques of the Seismic Traces Calibration for CTBT
Tech Area / Field
- ENV-MIN/Monitoring and Instrumentation/Environment
- ENV-SEM/Seismic Monitoring/Environment
3 Approved without Funding
NIIIT (Pulse Techniques), Russia, Moscow
- Institute of Dynamics of the Geosphere, Russia, Moscow\nCentral Experimental-Methodical Expedition of Geophysical Survey of RAS, Russia, Kaluga reg., Obninsk\nVNIITF, Russia, Chelyabinsk reg., Snezhinsk\nGEON, Russia, Moscow\nInstitute of Computational Mathematics and Mathematical Geophysics, Russia, Novosibirsk reg., Novosibirsk\nAltay-Sayan Experimental-Methodical Seismologic Expedition, Russia, Novosibirsk reg., Novosibirsk\nNational Nuclear Center of the Republic of Kazakstan / Institute of Geophysical Researches, Kazakstan, Kurchatov
- Preparatory Comission for the Comprehensive Nuclear-test-ban Treaty Organization, Austria, Vienna\nNORSAR, Norway, Kjeller
Project summaryThe aim of this Project is the development and experimental research of seismic trace calibration technique using chemical blasts of various configuration, study of geophysical wave field peculiarities and estimation of blasting technique efficiency in reference to the issue of consolidation of confidence measures in frames of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). This Project is directed to the study of peculiarities of geophysical wave fields arising while conduction of deepened chemical blasts and to demonstration of methods of their conduction and signals recording to develop the offers on their use for calibration of the International monitoring system of CTBT, and to collect ground truth data of known sources.
Proposals on the Project are aimed to collect ground truth data and velocity models useful for calibration in the different seismic areas.
Such high-quality ground truth events at a GT5 level or better (with absolute location and depth errors less than 5 kilometers) with magnitude not less then 2.5 will be obtained: a) from dense local networks, b) from instrumented mines, c) with remote sensing to regions that are difficult or impossible to access, and d) by dedicated calibration explosions especially reciprocal calibration shots. Researches of uncertainties in the acquired ground truth information will be provided. The ground truth data collection will be provided with geophysical studies that generate new ground-truth events and with source geometry information such as mining explosions or mining-related collapses.
At the stages of the experiments planning and realization the acknowledges how seismic energy is generated from underground phenomena and how this energy is partitioned between P and S waves, and also how the generation and partitioning of the seismic energy is affected by properties such as 1) source region medium and overburden, 2) the local structure, and 3) the surrounding tectonic province. Another question is: what is the physical basis for a measurable property, such as magnitude that can be directly related to the yield of a fully coupled explosion, and how do emplacement conditions effect the observation. The attempts to develop models that calibrate earth velocity and attenuation structure of regional phases Pn, Pg, Sn, Lg and surface waves in various Eurasia regions will be provided.
The attempts in improved modeling of waveforms at local, regional, and nearteleseismic distances (up to 2000 km) will be provided. In results of field experiments full waveform synthetic seismograms matching to data for seismic event detection, location, and discrimination will be improved.
Four tasks and associated subtasks will be conducted to accomplish this scope of work. The tasks are summarized as follows:
- Development and support of the data collection and management system.
- Development of IMS Calibration techniques Using Mining Shots.
- Development of IMS Calibration techniques Using Regional networks.
- Development of IMS Calibration techniques Using Special blasts.
7 Russian Institutions and 1 Kazakh will carry out these tasks.
Seismic trace calibration in the interests of CTBT verification contributes to the increase of accuracy of questionable seismic source localization and its subsequent identification. Use only of the earlier collected data on earthquakes and short-delay industrial explosions gives very raw estimations of event coordinates because of the difference of source mechanisms. The alternative vibration sources are characterized by limited zone of propagation of exited waves (up to 250-350 km), and do not allow realization of seismic trace calibration in regional zones of recording by the International Monitoring System (IMS) (500-2000km). At the same time shallow deepened blasts of chemical explosives, up to 30t mass, allow recording of seismic signals at distances of more than 1000 km. The restraining factor in use of blasting methods is a considerable cost of boring and blasting works, and the necessity of conducting tens of explosions at various distances and azimuths for calibration of one monitoring station (array of stations).
The proposed blasting methods assume subsequent conduction of a series of chemical explosive blasts with a value of mass in a range from a small mass - for calibration of near zone, to large masses (several tons) - for regional calibration. At the same time the results of recording signals from small explosions are used for selection of optimum configuration and for specifying mass of more powerful explosions. To reduce a number of blasts it is proposed to use seismological principle of reciprocity, and locate explosive source near IMS seismic station, and recording should be carried out in tens of stationary and temporary points situated in regional zone.
The theoretical part of the project assumes realization of account of a complete wave field of calibration explosions for station ZAL. The Boltzman model with aftereffect will be taken as the basis model. The initial data for accounts are: Vp, Vs, density of medium, and also either good quality Q or factors of attenuation in layers. Either explosion on depth or impact to free surface or distributed source is simulated as a source. The result of modeling is: seismograms either of surface or inside of medium, and also photos of fronts of waves at the various moments of time (seism films). The system of the integral-differential equations, which simulates the mentioned task, will be solved by the specially developed numerical methods.
It is assumed to carry out experimental works in the area of IMS seismic stations in the territory of Russia (no less then 2) and in the area of 1 - 2 stations in Kazakhstan, which are included in the IMS. Selection of stations is determined considering the possibility of regional recording at distances of an order of 1000 km. For verification of reciprocity principle at regional distances it is supposed to organize special blasts at operating quarries in the zone of selected IMS seismic stations. Seismic observations will be carried out in explosion’s near zone for provision of geoecological monitoring and specifying structure of the earth’s crust, in local zone for comparison with the results of recording signals from other explosive and vibration sources and for verification of reciprocity principle, and also in regional zone for obtaining preliminary data about the peculiarities and travel times of seismic waves propagation along various traces and study of a deep structure of region.
For taking of comparative estimations of blast techniques efficiency observations and data acquisition from alternative calibration sources (large industrial explosions) will be carried out. Observations of infrasound and other geophysical fields generated by powerful explosions will be carried out simultaneously with seismological observations in order to increase the efficiency of experimental works.
The results of data recording and processing will be archived in CSS3.0 Format compatible with the International Data Center format and will be introduced into the database of the prototype of Information and Analytical Center of NIIIT’s Monitoring System of chemical blasts and will be available for participants of the Project.
In the progress of works under the Project the analysis and generalization of experimental materials obtained using reciprocity method and direct seismic sounding method will be carried out. On the basis of a series of experiments with explosive excitation of seismic signals at various configurations of a network of seismic receivers and points of excitation the recommendations will be worked out pertaining to the arrangement and conduction of calibration experiments in the interests of the CTBT. Estimates of cost and duration of experimental works will be obtained.
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