فهرست مطالب

Seismology and Earthquake Engineering - Volume:24 Issue: 2, Spring 2023
  • Volume:24 Issue: 2, Spring 2023
  • تاریخ انتشار: 1402/06/14
  • تعداد عناوین: 6
  • On the GIS-based Seismic Risk Maps of Jablah City, Syria
    Ahlam Khalil *, Raed Ahmad, Mohamad Daoud Page 1

    Seismic risk assessment is a necessary study to mitigate future earthquake damage in urban area. Jablah city is an old coastal city in Syria; it had been affected by many historical earthquakes, and it has not been studied seismically yet. The seismic database in National Earthquake Center in Syria was used to calculate seismic hazard maps of the study area. These maps indicate that the values of the ground acceleration are increasing towards the north and southeast of the Jablah city. Field work on soil shows that dominant period values range from 0.34 to 2.5 seconds, and amplification factor values from 1.1 to 3.7. The period of free vibration of the buildings varied from 0.09 to 0.45 seconds for the selected buildings. To assess the current status of the buildings, an evaluation form of vulnerability has been prepared. As a result, the vulnerability coefficient of the studied buildings to seismic forces ranged from 0.3 to 0.6. To obtain seismic risk maps, GIS program was used to process multiple layers such as seismic hazard map, dominant period, amplification factor of soil, free vibration period of buildings and assessment of their current status. The results show that many crowded neighborhoods in Jablah city are located in high seismic risk areas where tall and important buildings are located. This confirms that the high potential of human and economic losses concentrated in the city center.

    Keywords: Risk Assessment, Seismic Hazard, Vulnerability, Dominant period, Amplification Factor
  • Possible Precursors Linked to the 2021 Fin Doublet Earthquakes
    Amin Abbasi *, Hamidreza Javan-Emrooz Page 2

    Precursors as informer pioneers of near future occurrence of earthquakes, are very diverse in their natures. We examined three short term possible precursors contain foreshocks, b-value variations, and amplitude abnormalities in the Very Low Frequency (VLF) radio signals for the November 14, 2021 Fin double-earthquakes (M > 6). By searching-zoom method in earthquakes one degree on each side of the hypocenter location in the Iranian Seismological Center (IrSC), the International Earthquake Engineering and Seismology (IIEES) and the Building and Hosing Research Center (BHRC) catalogs, those data for the reviewing foreshocks were provided, then they analyzed by use of ZMAP for the b-value changes based on the Guttenberg-Richter empirical relation methodology. Whereas, in the BHRC accelerometer portal reported 8 events before the main shock times, none of them are not in the other catalogs. The temporal b-value variations from the normal, shown non sharp fits to the rises or falls of the seismicity as an expected indicator. Some b-value in accordance with the seismic up and down rate tracks, have high spatial uncertainties. We observed some amplitude anomalies in the VLF received signals from mean standard deviation in VLF signal measurements (2σ criterion in the statistical method) in about 4 days before and up to 5 days after the main shocks. Albeit, in follow the null hypothesis, for verifying (and not refused) these relations, are needed to be qualified data. As you will see, all three catalogs used in the coverage, quality, verification and appropriate data for logical and reliable review and processing are not less error than the expected standards. The main goal has been to investigate the possible precursors before the 2021 Fin doublet earthquakes by using available local ground base data and obtainable facilities in this field and considering their improvement. The possibility of some foreshocks associated with double earthquakes cannot be ruled out. Therefore, the reliability of the studied precursors completely dependent to the proper data, that sufficient-precise instruments for their observations and recording are vital requirement. It is possible to use that kind of reliable and high-quality data in the analysis of pre-earthquake signals or even reasonable forecasting, which, if possible, will bring a valuable achievement in the future. We came to the conclusion that with such researches, the necessity of data quality and improving the level of their acquisition/standard in the country's research centers, must be carefully defined for more scientific and practical effects.

    Keywords: Earthquake, Precursor, Foreshock, b-value, VLF radio signals
  • The Role of Tear Faults on the Morphology and Seismic Activity of the Ashkhaneh Fault Zone, Kopeh-Dagh, NE Iran
    Saeid Rahimzadeh *, Noorbakhsh Mirzaei Page 3

    The Kopeh-Dagh zone of NE Iran is dominated by active strike-slip and thrust faults that accommodate a part of the convergence between the Arabian and Eurasian Plates. The Ashkhaneh thrust fault zone with approximately 80 km long is one of the main accommodative structures which has been dissected by a number of strike-slip tear faults. Tectonic geomorphology, satellite-based Global Positioning System (GPS), and seismic data imply that the development of tear faults is one of the main controlling factors in structural deformation and related seismic activity along the Ashkhaneh thrust fault zone. The tectonic activity of the Ashkhaneh fault zone is mainly due to the E-W trending range-parallel reverse faults and NE-SW to ENE-WSW trending range-crossing left-lateral strike-slip tear faults coming from two stages. In the first stage, the major E-W trending Ashkhaneh thrust fault zone has been developed in response to the collision of Central Iran with the South Caspian Basin. In the second stage, the progressive N-S shortening resulted in mountain curvature in eastern Alborz and the formation of strike-slip tear faults in response to the differential shortening along the Ashkhaneh fault zone. The sense of slip and geometry of the tear faults and the Ashkhaneh thrust fault seems to provide insights into faults interaction, so that the likely movement along one of these faults may cause reactivation of the other fault(s); similar to the earthquake occurrences on the Shalgun-Yelimsi tear fault (2019/11/07, Mw 5.9) and South Bozgush thrust fault (2019/11/10, Mw 4.4) in northwestern Iran.

    Keywords: active tectonics, Tear fault, Faults interaction, Ashkhaneh fault zone, Kopeh-Dagh, Northeast Iran
  • Determination of the Fault Plane of the 2017 Iranian Sefidsang Earthquake, Mw 6.0, by Seismic Moment Tensor Inversion Method
    Ali Songhori, Mehrdad Pakzad *, Ahmad Sadidkhouy, Zahra Khorrami Page 4

    Essentially, assuming a simple fault model, the hypocenter and centroid should be located on the same plane. This approximation can help to distinguish the fault plane from the auxiliary plane of an earthquake in many situations. On April 5, 2017, the Sefidsang earthquake Mw 6 occurred in north-eastern Iran. It was not possible to relate a fault to the earthquake according to the reports of the Iranian seismological center (IRSC) and the International Institute of earthquake engineering and seismology (IIEES) of Iran. The association of the earthquake to the western part of the Fariman fault or to the southern end of the Kashfroud fault is not possible. In this study, data from the stations of the aforementioned agencies was used to model the earthquake waveforms, and an effort was made to find the focal mechanism of this earthquake, investigate it, and also to eliminate the ambiguities that exist in determining the fault plane of the earthquakes using the Hypocenter-Centroid (H-C) method, due to the higher accuracy in simulating the waveforms and finding the centroid point of earthquakes in local and regional distances. we obtain the fault plane with a strike of 324 and dip of 44 degrees, which indicates the northwest-southeast trend, parallel to the trend of the Kashfroud fault. This has good agreement with the results of other researchers.

    Keywords: H-C Method, Focal mechanism, Kashafroud fault, ISOLA
  • A Comprehensive Probabilistic Seismic Hazard Analysis of Karaj, Iran Using Classical and Monte Carlo Simulation Approaches
    Mina Rashidirad, Nazila Kheirkhah, Erfan Firuzi * Page 5

    This study provides a comprehensive probabilistic seismic hazard assessment for Karaj, the capital of Alborz province. In the present study, two probabilistic approaches including the classical and Monte Carlo methods are applied. In this regard, the most recent earthquake catalog of the region, as well as, the most appropriate GMPEs based on the statistical tests of the likelihood and the log-likelihood are used. The results indicated that there are differences between the results of two approaches, which is intensified in the longer return periods. This disparity mainly stemmed from the different concept of two methods for incorporating the aleatory uncertainty. In classical PSHA, the aleatory uncertainty takes into account using the integration which is truncated at a fixed number of the logarithmic standard deviation. While, in the Monte Carlo simulation approach, the aleatory uncertainty is considered in calculation using random sampling of GMPEs variability. In addition, the ground motion shaking map of the region for the dominant seismic scenarios including the rupture of the North-Tehran and Eshterhard faults are developed. These seismic scenarios have the potential of producing the greatest acceleration; consequently, the most vulnerability. The outcomes of this study can be used for providing urban plan or estimating the probable economic and casualty losses of Karaj.

    Keywords: Probabilistic Seismic Hazard Assessment, Classical Seismic Hazard Analysis, Monte Carlo Simulation, Karaj, Iran
  • Numerical Modeling of a New Mitigation Measure for Reverse Surface Fault Rupture Hazards Effects on Buildings
    Mahtab Shiravi, Mojtaba Moosavi * Page 6

    Surface fault rupture can lead to significant harm to engineered structures and facilities due to differential displacement in the ground. With the growing demand for land use, it might become essential to implement strategies to protect structures against hazards arising from fault rupture propagation. This study examines a novel mitigation approach utilizing an underpinning technique. To lessen foundation rotation during a fault rupture, a pile similar to the underpinning technique is employed beneath the foundation. This pile is not used to reinforce the main foundation; rather, it serves as a structural element to reduce hazards during a fault rupture with the removed support between the foundation and the pile. The effectiveness of this pile in the soil under the structure is evaluated through a series of numerical models. The findings suggest that while this pile is effective in mitigating the dangers of surface fault rupture, such as building rotation, its application should be guided by comprehensive geotechnical investigation given the complex nature of fault-foundation interaction issues.

    Keywords: Fault rupture, Soil-Structure Interaction, Mitigation, piled foundation