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Recent Seismological Research of the Caspian Basin

Keith Priestley, Bullard Labs, Mikhail Rozhkov, SYNAPSE Science Center

The paper reflects the state of recent basic seismological research of the Caspian Sea basin. Being one of the main instruments for studying the Earth's deep structure, modern seismological techniques are based upon new data, collected with the help of modern technologies of data acquisition. Present seismic installations of the Caspian Basin, jointly operated by scientists from different countries, highly satisfy such concepts. Two major massive experiments must be mentioned here: (1) joint Russian-British program CSN on studying South Caspian Basin structure conducted by the University of Cambridge (UC), UK, and SYNAPSE Science Center (SSC), Russia, and (2) small aperture array (SAA) program conducted by the Incorporated Research Institutions for Seismology of the United States (IRIS). Both programs are being performed with the technical support of the Institute of Seismology of Turkmenian Academy of Sciences. Program (2) was mainly performed by the University of California San Diego during the past 2 years. Huge amounts of data, recorded by more than 50 instruments of so called "seismic antenna" near the city of Ashgabad, soon will be available for the scientific community through the IRIS Data Management System (if you are; Internet user, check wvvw.iris.washington.edu). In current paper, we would like to describe progress made within the framework of program CSN (Caspian Seismic Network), and relative activity at the SSC.

Caspian Seismic Network. CSN research project was started for better understanding seismic structure of the south Caspian Basin and the surrounding region. To accomplish this we have installed a number of broad-band digital recording seismographs around the Caspian and operated these for about two years. Data at each CSN station is recorded on a Refraction Technology 72a-02 data loggers which are equipped with either Omega or GPS external hard disks and a Guralp CMG-3T triaxial broadband feedback seismometers. During next 2 weeks one more site will be equipped with the same instruments nearby the city of Kara-Kala (KAR). In Azerbaijan the stations LNK and BAK, later moved to Shemakha (SHE), are operated in cooperation with Dr. S. Agamirzoev from the Geophysical, Azerbaijan. In addition to the data from our seismograph network, this study data from the IRIS seismograph station near Ashgabad, Turkmenistan (ABKT). We expect, that the output of the study may find application in solving next problems:

  • Clearing the character of the modern geodynamic process, playing significant role in aa leveling regime of the Caspian basin, and so forming ecological situation of he coastal areas
  • Establishing possible connection between Caspian water level regime and the generating ng earthquakes in the surrounding regions;'
  • Clearing the role of the Caspian geodynamics in mud-volcanic activity, sudden mud-gas outbursts, causing economic and human losses;
  • Creating detail velocity structure to improve the precision of seismic sources location;
  • Design of urban developing of the coastal area, that is connected with reliable data on seismic risk at this territory;
  • Establishing possible connection between recent submerge of the Gulf of Kara-Bogaz-Gol and geodynamic processes. Presently more than 50 cubic kilometers of Caspian waters a year fill the Gulf. This may play significant role in terms of the induced seismicity, especially for 5 western Turkmenistan, where one of the largest world earthquake occurred in the year of 1895 nearby Krasnovodsk (M=8.2).

Historical Seismogram Processing

We also touch here such important aspect as re-interpretation of old recordings of Deep Seismic Sounding (DSS) experiments. DSS data significantly our knowledge about the structure of the area under research. For the Caspian there are many paper records of DSS data, created during the marine experiment of the year of 1956. Totally there were 2500 km of the profiles, located mainly in the Central south. The area covered by the profiles is overlapped by the area of 5 paths between the Turkmenian and Azerbaijanian recording sites. So using data may improve seismic models which are to be created after processing the appropriate amount of data. Some records were digitized manually on the devices with rather poor precision, some have never been digitized at all. There are big archives of paper records ;in Russia and Azerbaijan, which are precious for science and tend to be corrupted by time if natural decay. Also, even results produced earlier with a part of historical materials nrrd to be re-interpreted by using advanced processing techniques, which would require advanced digitizing procedures. For this purpose DGS software package (automated digitizing software for scanned images) working under UNIX operating system was developed at the SSC. We have already started to create an archive of digital data and images of scanned paper records related to the Caspian Basin, as well as a database of processed data and experiment's parameters. This work is being performed at the Local Area Network of the SSC equipped with SUN Workstations and PCs working under UNIX. Outside users will have an access to the database via Internet using our WWW server www.synapse.ru.

Data processing

Presently two groups of scientists - at the Cambridge University and at the SYNAPSE Science Center - work on the CSN data processing. The work at the SSC includes mainly event association with HDF and PDE catalogues, local and regional events location, and creation of epicenter's map. For this purpose we use a package SNDA (Seismic Network Data Analysis), developed by the SSC. As soon as the database of the regional events will be created at the SSC, we will use several advanced techniques, tested on another sets of data. For example, we expect satisfactory results using artificial neural networks (back-propagation, cascade correlation and clustering) for depth determination and wave field animation. This modeling will possibly require results on receiver function analysis, received at Cambridge.

Acknowledgments

The success of the CSN experiment was achieved because of great job done by SSC staff scientist Vasily Kiselevich on array operation and data collection/processing. The help of Andrey Rasskazov on hardware support, Alexey Chulkov on data processing, and Eugeny Kapitchnikov on paper preparation is also significant. We also thank Dr. Batyr Karryev for his contribution to this research.

Cambridge University SYNAPSE Science Center/ Moscow IRIS Data Analysis Center, Russia

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