Wyniki wyszukiwania - BazTech

1

Seismic site characterization considering directional near‑field seismogenic active faults in Aswan area, Egypt

Thabet Mostafa, Omar Khaled, Mohamed Abdel Nasser, Osman Mohamed

Acta Geophysica

|

2023

|

Vol. 71, no. 3

1119--1148

EN

Aswan area in South Egypt experiences continuous seismic activity due to seismogenic active faults, particularly Kalabsha and Seiyal active EW faults. The seismic site characterization is not properly identified, although the presence of high-density distribution of earthquake stations. The present study investigates fourteen earthquake stations of the Egyptian National Seismic Network, as well as six microtremor measurement sites. We analyzed ground motions due to seismogenic active faults recorded at surface from these fourteen earthquake stations. We measured microtremors for up to 120 min with portable seismometers at six sites in the vicinity of the High Dam area. The horizontal-to-vertical spectral ratios of earthquakes (EHVSR) and microtremors (MHVSR), their plots as a function of frequency and direction of motion, and diffuse field inversion are used in the study. Therefore, we could provide an obvious understanding of the site characterization including resonance frequencies, directional amplifications, and back-calculated subsurface velocity structures at these stations and sites. We found three predominant amplification directions of NS, EW, and NE–SW due to the horizontal components of the seismic waves. These amplification directions are near-transversal ~ transversal to the NS and EW strikes of the active fault system in the study area. In time–frequency analyses of the records, this directionality is observed clearly for S-wave and surface wave time windows. We validated the diffuse field inversion process not only using fitting between observed and inverted EHVSRs and MHVSRs, but also using available geological 2D cross sections and hydrological information in Aswan area.

2

Calibration of the spectral ratio pyrometers on VGA-matrices of photo detectors

Firago V., Sencov A., Wójcik W.

Przegląd Elektrotechniczny

|

2008

|

R. 84, nr 3

164-167

EN

The paper describes a calibration method of spectral pyrometer made up of several VGA photodetectors, that utilizes black body model and tungsten incadescent lamp.

PL

Artykuł opisuje metodę kalibracji pirometru spektralnego utworzonego z wielu fotodetektorów VGA przy użyciu modelu ciała czarnego i wolframowej lampy żarzeniowej.

3

Application of the horizontal to vertical spectral ratio technique for estimating the site characteristics of ground motion caused by mining induced events

Olszewska D., Lasocki S.

Acta Geophysica Polonica

|

2004

|

Vol. 52, nr 3

301-318

EN

The work presents an attempt of application of the horizontal-to-vertical spectral ratio (HVSR) method for estimating the local amplification of ground motion caused by mining seismic events in the Legnica Głogów Copper District. Amplifying properties of the surface layer are assessed from the ratio of amplitude spectra of the horizontal and vertical components of ground acceleration, recorded at the surface. The location of a local maximum of the ratio in the frequency band up to 8 Hz assigns the resonant frequency of the surface layer; the maximal value estimates the amplification factor at the measurement point. The spectral ratio was evaluated for 219 ground acceleration records from ten recording stations. The HVSR curves for induced seismicity turned out to be similar to the typical HVSR-s for natural earthquakes. Amplification factors estimated by the HVSR method were used to reduce the observed peak ground accelerations (PGA-s) to the bedrock. The reduction significantly improved an agreement beween the PGA values order and the order of epicentral distances. The obtained results suggest that the HVSR method can be successfully used to evaluate the local influence of the surface layer also for induced seismicity, in spite of the fact that in this case the conditions for application of the method essentially differ from the conditions met in natural seismicity.