A quantitatively new analog-to-digital converter (ADC) module has been developed during 2010, in co-operation with Tedia Ltd. The module has a 28-bit final resolution and uses 32-bit arithmetic. There are two versions, with four and twelve analog inputs. The 4-input module replaces the original 21-bit version, produced until 2009. The 12-input module is intended to be deployed in small-aperture seismic arrays. The whole set consists of four 3-channel detached modules that can be interconnected with the main module using a cable of up to 100 m in length. This design increases signal-to-noise ratio (SNR) by placing the A/D part as close to the seismograph as possible in order to transmit digital data for storage. All channels are sampled coherently so that all four sensors are automatically synchronised. It allows the detection of local events even though the sync-signal is absent. In other words, the 12-input module is suitable for ad-hoc field measurements even in places where there is no GPS signal. All arrays operated by the Institute of Rock Structure and Mechanics (IRSM) are going to be upgraded to use these modules and some new sites will also be set-up with this innovative equipment (e.g. Lazy in Western Bohemia and Dobrá Voda in Slovakia)., Milan Brož and Jaroslav Štrunc., and Obsahuje bibliografii
A novel method called Generalized Average of Signals (GAS) for detection of very weak waves in seismograms is describe d and tested. The general principle of the GAS method is to take advantage of the cohe rency of the signal, which is extracted. The signals are shaped with moving window and converted to the frequency domain. Then they are non-linearly summed considering their complex representation (a mplitudes and phases). The method impr oves signal-to-noise ratio of coherent seismograms considerably. The GAS method is tested on sy nthetic seismograms and comp ared with the PWS method., Jiří Málek, Petr Kolínský, Jaroslav Štrunc and Jan Valenta., and Obsahuje bibliografické odkazy
In October 2005 local seismic monitoring started in the area of the Hronov-Poříčí Fault Zone. In the present paper we summarize seismic measurements using a small-aperture seismic array Ostaš. Parameters of the array and methodology of the data registration and processing are described. The list of local microearthquakes during two years of registration is presented., Jiří Málek, Milan Brož, Vladimír Stejskal and Jaroslav Štrunc., and Obsahuje bibliografické odkazy
The NKCA and KVCA small-aperture (~ 90 m) seismic arrays in western Bohemia represent the second deployment of this type in the Czech Republic. The arrays have a regular triangular geometric configuration with high gain three-component seismographs in each corner of the triangle. This allows very weak local earthquakes to be detected with a high degree of precision and, thereby, substantially enhances the results of the pre-existing local seismic network (WEBNET). This paper reports on the pilot measurement period. It summarises the final configuration of the arrays and compares the derived results. The measured data have been analysed using the DP/EP system developed by NORSAR. This incorporates several array techniques such as beamforming, f-k analysis, and the cross-correlation method. It has been shown that during the study period, the levels of seismic activity recorded by the seismic arrays were up to fifteen times greater than the levels recorded by the pre-existing seismic network., Jaroslav Štrunc and Milan Brož., and Obsahuje bibliografii