List of articles (by subject) Geophysics
-
Open Access Article
1 - Determination of body waves quality factor in the NW Iran, with power spectrum analysis
Hooman Latifi Reza Heidari Noorbakhsh MirzaeiAs one of the ways to identify seismological characteristics in the region, determining the quality factor of seismic mapping can provide valuable information about inside the earth. This study investigates local site effects as a function of frequency and presents a ne MoreAs one of the ways to identify seismological characteristics in the region, determining the quality factor of seismic mapping can provide valuable information about inside the earth. This study investigates local site effects as a function of frequency and presents a new relationship for determining the quality factor in northwestern Iran with regard to local site effects. These sites are selected so that their signal-to-noise ratio (SNR) is greater than 5. This study uses the Short-Time Fourier Transform (STFT) method in which a fixed time window and its multiplication by a given signal are used. The coefficients resulting from this transformation are considered as wave amplitudes at any frequency by performing a short-time Fourier transform. The amount of power spectrum decay is used instead of the ground displacement amplitude decay. Local site effects and kappa, a function of the path and site effects, were investigated and became the basis of spectral decay calculations. The results of this study were compared with those of the previous study based on conventional and classical methods and the accuracy of the methods was evaluated using standard deviation (SD) values. Finally, the quality factor equations were obtained for the North-South component (N-S) as Q(f)=(78±2)f^((1.37±0.02)), for the East-West component (E-W) as Q(f)=(62±2)f^((1.5±0.03)), and for the vertical component (Z) as Q(f)=(87±2)f^((1.29±0.03)). Manuscript profile -
Open Access Article
2 - Near surface cavities mapping using integrated geophysical techniques: Case study of Gadwalian dam, North Pakistan
Waqar Ahmad Khaista Rehman Muhammad Farooq Asghar Ali Tanveer AhmedIntegrated geophysical techniques have always been useful in identifying subsurface features. In the present study, three integrated geophysical methods of ground-penetrating radar (GPR), resistivity and Multi-channel Analysis (MASW) of surface waves have been utilized MoreIntegrated geophysical techniques have always been useful in identifying subsurface features. In the present study, three integrated geophysical methods of ground-penetrating radar (GPR), resistivity and Multi-channel Analysis (MASW) of surface waves have been utilized for near surface studies and identification of subsurface cavities near the Gadwalian dam. Acquisition of four inline and crossline profiles through GPR (100 MHz shielded antenna), two resistivity profiles through Imaging system and six seismic refraction profiles (MASW) have been made on the selected site having potential subsurface cavities. The processing and interpretation of GPR data through different software’s exhibit variations in amplitude/diffraction patterns and several cavities have been identified in the GPR profiles. Sweetness attributes applied on the GPR data set also validate the cavities and unsaturated/saturated fractures. Slate beds and cavities have also been identified on pseudosections obtained through resistivity imaging. Further studies on 2D shear velocity (Vs30) profiles using MASW analysis for interpretation suggested that the absence of low velocity layer in shallow surface and velocity increase with respect to depth. Manuscript profile -
Open Access Article
3 - Microtremor analysis to evaluate BMKG region III building, Bali, Indonesia
Muh Sarkowi Rahmat Wibowo Ida Bagus Yogi Mahmud Yusuf Yohana BokaBali Island has experienced more than 6 significant earthquakes (magnitude > 6) since 1815, which caused extensive damage to buildings and casualties. The microtremor data analysis in the building of Indonesian meteorology, climatology and geophysics agency (BMKG) Re MoreBali Island has experienced more than 6 significant earthquakes (magnitude > 6) since 1815, which caused extensive damage to buildings and casualties. The microtremor data analysis in the building of Indonesian meteorology, climatology and geophysics agency (BMKG) Region III Denpasar aims to reduce the risk of building damage and casualties due to the earthquake. The analysis was conducted by measuring microtremor and processing the data to obtain the natural frequency of the soil (f0s HVSR) and building (f0b HVSR), resonance, soil (Kg), and building vulnerability index (Kb) so that the safety of the building can be known in the event of an earthquake. The processing and analyzing results the characteristics of microtremor data get the f0b has a greater value than the f0s value so that the building is relatively safe from resonance. The resonance value of the building with the ground has an (R) value of 6.67% - 13.3%, with an average resonance value of 8.89% which is included in the medium resonance. The location of the building is in an area with a Kg of 8.20 – 10.81, which is included in the category of low to moderate soil vulnerability index, and the Kb has a value of 0.4827x10-6 – 7.9771x10-6, with the first floor having an index highest vulnerability. The f0s, f0b, R, Kg, and Kb show that the building is in the safe category in the event of an earthquake. Manuscript profile -
Open Access Article
4 - Resistivity surveys application for detection of shallow caves in a case example from Western Iraq
Ali Abed Kamal Ali Asama Al-HadithyThe 2-D and 3-D imaging resistivity techniques were used in the current study to determine the shallow subsurface caves in the Haditha region, western Iraq. The 2-D resistivity imaging has been applied at five locations. The dipole-dipole arrangement was selected with a MoreThe 2-D and 3-D imaging resistivity techniques were used in the current study to determine the shallow subsurface caves in the Haditha region, western Iraq. The 2-D resistivity imaging has been applied at five locations. The dipole-dipole arrangement was selected with an electrode spacing of 2 m. The inverted models show the anomalous resistivity variation between the background rocks and the voids. Which showed shallow cavities at 1 to 6 m depth, whereas some of them are extending to a depth of 23 m. The unconformity layer between Anah and Euphrates formations is the lowest cohesive than the rocks beneath and above it. Providing the best area for the caves to be formed resulted from dissolving its rocks by leaking rainwater and groundwater. The 3-D resistivity imaging technique was selected near some visible caves by collating seven 2D imaging lines in mapping the subsurface extent of such cavities. 3D imaging draws a sub-surface image in presence of 3D inhomogeneity such as caves. The horizontal slices of 3D models show up these caves with anomalous high resistivity at 0-0.80 m, 0.80-1.72 m, 1.72-2.78 m, and 2.78-3.99 m depths. It also shows a group of small caves, such as the sink-hole canals that connect the main cave to the surface. Both 2-D and 3-D resistivity models have marked a very similar spread of subsurface caves in the study area and show some caves, in the upper part of the unconformity layer. The large values of RMS error for models, attributed to the presence of large homogeneities in the study area. Such heterogeneities are mainly caused by a large variation in the subsurface resistivity of the rocks surrounding the caves and the large spread of shallow caves. Manuscript profile -
Open Access Article
5 - Hazard functions and conditional probability of earthquake occurrences in major fault zones in Turkey
Hakan KaracaAmong several distribution characteristics, temporal distribution characteristics of earthquakes provide the most crucial information on the temporal patterns of past seismicity. Identification of such patterns is required for seismic hazard, forecast studies and also s MoreAmong several distribution characteristics, temporal distribution characteristics of earthquakes provide the most crucial information on the temporal patterns of past seismicity. Identification of such patterns is required for seismic hazard, forecast studies and also simulation of future seismicity. The confusion of how to model the past temporal patterns does limit further development:. Though the Poisson model is routinely used in hazard modelling, its validity is often questioned. Furthermore, the question as to which model best represent past temporal patterns of earthquake occurrence is not answered yet. Within this context, in this study, to investigate the interevent time (IET) distribution, two seismically active regions in Turkey are selected where the seismic activity never diminishes and the hazard remains high. These regions, namely the western end of the North Anatolian Fault Zone and East Anatolian Fault Zone are known to produce moderate or large magnitude earthquakes. Four distributions, namely, exponential, gamma, Weibull and lognormal models are tested for how well they fit the earthquake records of the two faults, and importantly, the hazard functions that is instantaneous rate of occurrence of events, and conditional probabilities are also developed for performance evaluation. In the end, it is observed that, each model has flaws in identification of temporal pattern of earthquake occurrences and forecasting earthquakes. Manuscript profile