The procedures and interpretation of the magnetic data measured over the Mid-Atlantic Ocean Ridge by Swarm-A satellite is discussed in this paper. The data processing procedure has four phases after the data format conversion. The first phase is the selecting data whose Kp index is lower than 1. Secondly, the main magnetic field should be subtracted from the measured data for example through the IGRF model. This step is followed by removing trend, related to the satellite trajectory. The final step is eliminating the dipole nature of the magnetic field via Reduction to the Pole (RTP). Nonetheless, the RTP process might cause misinterpretation over the large study area and lower latitudes. Therefore, the amplitude of the analytic signal (AS) is used as an alternative to the RTP. The qualitative interpretation of the magnetic anomaly is conducted via AS anomaly, bathymetry, heat flow and tectonic map. Quantitatively correlation coefficients of bathymetry and heat flow with respect to AS are interpreted.
{"title":"Interpretation of the magnetic anomalies over the Mid-Atlantic Ocean Ridge using Swarm-A satellite","authors":"Ilkin Özsöz, Ankaya Pamukçu","doi":"10.15233/gfz.2022.39.3","DOIUrl":"https://doi.org/10.15233/gfz.2022.39.3","url":null,"abstract":"The procedures and interpretation of the magnetic data measured over the Mid-Atlantic Ocean Ridge by Swarm-A satellite is discussed in this paper. The data processing procedure has four phases after the data format conversion. The first phase is the selecting data whose Kp index is lower than 1. Secondly, the main magnetic field should be subtracted from the measured data for example through the IGRF model. This step is followed by removing trend, related to the satellite trajectory. The final step is eliminating the dipole nature of the magnetic field via Reduction to the Pole (RTP). Nonetheless, the RTP process might cause misinterpretation over the large study area and lower latitudes. Therefore, the amplitude of the analytic signal (AS) is used as an alternative to the RTP. The qualitative interpretation of the magnetic anomaly is conducted via AS anomaly, bathymetry, heat flow and tectonic map. Quantitatively correlation coefficients of bathymetry and heat flow with respect to AS are interpreted.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46898870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A statistical post-processing forecast system for medium range predictions using the GFS model has been developed for Jharkhand (India) with the aim of improving rainfall and temperature predictions for agricultural applications. The basis of the integrated block level forecast system (IBL-FS) build includes (i) Decaying weighted mean (DWM) bias correction technique, (ii) Value addition and (iii) Inverse distance squared weighted (IDSW) interpolation. In the first step, model bias corrected district level forecast for 24 districts of Jharkhand is generated from the output of numerical GFS model (T1534L64) by applying DWM bias correction technique. In the second step, these bias corrected forecasts are value-added using forecast from various NWP models and synoptic methods. Finally in the third step, the IDSW interpolation method is used to generate the forecast at an unmeasured block from the value-added district level forecast of the surrounding districts. The value-added forecast for 263 blocks for the state Jharkhand is prepared up to medium range time scale (120h). The performance skill of IBL-FS is evaluated for rainfall during monsoon season 2018 and 2019, for minimum temperature during winter season 2019, and for maximum temperature during summer season 2019 using different statistical metrics. The skill of IBL-FS is found to be higher than the direct model forecast (DMFC) by 15% to 43% for minimum temperature, by 18% to 41% for maximum temperature, and by 22% to 30% for rainfall forecast for day1 to day5 forecasts. This study concludes that the integrated approach is more skillful than DMFC for real time forecasts and useful for farming for the blocks of Jharkhand.
{"title":"Development of a NWP based Integrated Block Level Forecast System (IBL-FS) using statistical post-processing technique for the state Jharkhand (India)","authors":"S. D. Kotal, R. Sharma","doi":"10.15233/gfz.2022.39.6","DOIUrl":"https://doi.org/10.15233/gfz.2022.39.6","url":null,"abstract":"A statistical post-processing forecast system for medium range predictions using the GFS model has been developed for Jharkhand (India) with the aim of improving rainfall and temperature predictions for agricultural applications. The basis of the integrated block level forecast system (IBL-FS) build includes (i) Decaying weighted mean (DWM) bias correction technique, (ii) Value addition and (iii) Inverse distance squared weighted (IDSW) interpolation. In the first step, model bias corrected district level forecast for 24 districts of Jharkhand is generated from the output of numerical GFS model (T1534L64) by applying DWM bias correction technique. In the second step, these bias corrected forecasts are value-added using forecast from various NWP models and synoptic methods. Finally in the third step, the IDSW interpolation method is used to generate the forecast at an unmeasured block from the value-added district level forecast of the surrounding districts. The value-added forecast for 263 blocks for the state Jharkhand is prepared up to medium range time scale (120h). The performance skill of IBL-FS is evaluated for rainfall during monsoon season 2018 and 2019, for minimum temperature during winter season 2019, and for maximum temperature during summer season 2019 using different statistical metrics. The skill of IBL-FS is found to be higher than the direct model forecast (DMFC) by 15% to 43% for minimum temperature, by 18% to 41% for maximum temperature, and by 22% to 30% for rainfall forecast for day1 to day5 forecasts. This study concludes that the integrated approach is more skillful than DMFC for real time forecasts and useful for farming for the blocks of Jharkhand.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49520584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiayong Yan, Xu Wang, Yongqian Zhang, Chong Zhang, Fan Luo, Zhihui Wang
Edges detection and enhancement techniques of potential field data (gravity and magnetic data) are useful tools for finding the locations of anomalies at depth. Recently, these methods, including derivative-based filters, local phase filters and statistics-based techniques, have been increasingly widely used in solving geology problems, such as identifying subsurface faults, contacts, and other tectonic features. Nevertheless, general methods may not provide meaningful results for potential field data with heavy noise. To overcome these disadvantages, we present a new method named Varimax Norm (VariNorm) with a moving window to estimate the location of potential field data. Tests performed on the synthetic and field data in Tonling ore district show that the method does not require horizontal or vertical derivative calculations of any order, resists noise in nature and outperforms other traditional methods in a strong noise environment.
{"title":"Korištenje Varimax Norm metode za poboljšanje i prepoznavanje rubnih podataka polja potencijala","authors":"Jiayong Yan, Xu Wang, Yongqian Zhang, Chong Zhang, Fan Luo, Zhihui Wang","doi":"10.15233/gfz.2022.39.1","DOIUrl":"https://doi.org/10.15233/gfz.2022.39.1","url":null,"abstract":"Edges detection and enhancement techniques of potential field data (gravity and magnetic data) are useful tools for finding the locations of anomalies at depth. Recently, these methods, including derivative-based filters, local phase filters and statistics-based techniques, have been increasingly widely used in solving geology problems, such as identifying subsurface faults, contacts, and other tectonic features. Nevertheless, general methods may not provide meaningful results for potential field data with heavy noise. To overcome these disadvantages, we present a new method named Varimax Norm (VariNorm) with a moving window to estimate the location of potential field data. Tests performed on the synthetic and field data in Tonling ore district show that the method does not require horizontal or vertical derivative calculations of any order, resists noise in nature and outperforms other traditional methods in a strong noise environment.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":"1 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67353930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The contribution of PM10 to the daily Air Quality Stress Index (AQSI) was examined in a heavily affected industrial city of Eastern Mediterranean (Aspropyrgos, Greece). For this purpose, hourly values of four pollutants (SO2, NO2, O3, and PM10) were analyzed between 2012 and 2020, revealing that the main contributor to AQSI levels came from PM10 (between 17% and 90% to the daily AQSI), with a moderate annual variability and a spring peak. Excluding PM10, the AQSI always remained below the threshold of 0.8. To identify the atmospheric source of PM10 peaks, the Flextra - Air mass trajectories model was applied to 47 cases when the upper thresholds were exceeded. The empirical results of the model show that dust transport episodes, mainly from Sahara Desert, contribute to the daily levels of PM10 and, for generalization, to AQSI.
{"title":"PM10 and the air quality stress index in an industrial city of Eastern Mediterranean","authors":"Eleni Verouti, Dimitrios Gavathas, Anastasios Mavraki","doi":"10.15233/gfz.2022.39.4","DOIUrl":"https://doi.org/10.15233/gfz.2022.39.4","url":null,"abstract":"The contribution of PM10 to the daily Air Quality Stress Index (AQSI) was examined in a heavily affected industrial city of Eastern Mediterranean (Aspropyrgos, Greece). For this purpose, hourly values of four pollutants (SO2, NO2, O3, and PM10) were analyzed between 2012 and 2020, revealing that the main contributor to AQSI levels came from PM10 (between 17% and 90% to the daily AQSI), with a moderate annual variability and a spring peak. Excluding PM10, the AQSI always remained below the threshold of 0.8. To identify the atmospheric source of PM10 peaks, the Flextra - Air mass trajectories model was applied to 47 cases when the upper thresholds were exceeded. The empirical results of the model show that dust transport episodes, mainly from Sahara Desert, contribute to the daily levels of PM10 and, for generalization, to AQSI.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42462282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present hourly sea levels at Bakar tide-gauge station, located on the east coast of the Adriatic Sea. The station was established in 1929. The recorded data represent the longest time series of an oceanographic parameter measured in Croatia. They have been used in various scientific studies and practical applications. Sea levels were collected using float-type chart-recording tide gauge to which two digital instruments have been added recently. We describe station's location, its operational history, maintenance, principle of measurements, recorder zero checks and practice, and leveling history. Details on data sampling, quality checks and processing are included. Also, a brief summary of the most important results derived from these data is given and some practical applications are mentioned. The data are available through SEANOE (Međugorac et al., 2021; https://doi.org/10.17882/85171).
我们在位于亚得里亚海东海岸的巴卡尔潮汐测量站提供每小时的海平面。该站建于1929年。记录的数据是克罗地亚测量到的最长时间序列的海洋学参数。它们已被用于各种科学研究和实际应用。海平面是用浮式海图记录潮汐计收集的，最近又增加了两台数字仪器。我们描述了该站的位置、运行历史、维护、测量原理、记录仪零检查和实践以及水准历史。包括数据抽样、质量检查和处理的细节。此外，还简要总结了从这些数据中得出的最重要的结果，并提到了一些实际应用。数据可通过SEANOE (Međugorac et al.， 2021;https://doi.org/10.17882/85171)。
{"title":"Long-term measurements at Bakar tide-gauge station (east Adriatic)","authors":"Iva Međugorac, M. Pasarić, M. Orlić","doi":"10.15233/gfz.2022.39.8","DOIUrl":"https://doi.org/10.15233/gfz.2022.39.8","url":null,"abstract":"We present hourly sea levels at Bakar tide-gauge station, located on the east coast of the Adriatic Sea. The station was established in 1929. The recorded data represent the longest time series of an oceanographic parameter measured in Croatia. They have been used in various scientific studies and practical applications. Sea levels were collected using float-type chart-recording tide gauge to which two digital instruments have been added recently. We describe station's location, its operational history, maintenance, principle of measurements, recorder zero checks and practice, and leveling history. Details on data sampling, quality checks and processing are included. Also, a brief summary of the most important results derived from these data is given and some practical applications are mentioned. The data are available through SEANOE (Međugorac et al., 2021; https://doi.org/10.17882/85171).","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42920532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Markušić, N. Malaeva, S. Suchshev, I. Gabsatarova, N. Frolova
This paper is devoted to applications of the “Extremum” loss simulation system to two damaging earthquakes which occurred in Croatia in 2020. We provide a calibration procedure of mathematical models used for shaking intensity simulation. The regional macroseismic field parameters, such as the coefficients in the macroseismic field equation; the ratio between the longer (b) and the shorter (a) axes of the higher elliptical isoseismals (the flattening ratio k); the angle that specifies the orientation of the macroseismic field, in particular, the azimuth of the longer axis in the isoseismal ellipse, were all based on extensive macroseismic data acquired for the Balkan region and on the data for an analogous area with similar seismotectonic parameters in the Caucasus. We obtained a fairly good consistency between the results of simulation applied to the impact of the 2020 Croatia earthquakes and observations, confirming that the calibration of the macroseismic model by the Extremum system was both reasonable and effective for enhancing reliability for real time loss estimation.
{"title":"Calibration of shaking intensity models of the “Extremum” system to simulate loss due to the 2020 Croatia earthquakes","authors":"S. Markušić, N. Malaeva, S. Suchshev, I. Gabsatarova, N. Frolova","doi":"10.15233/gfz.2021.38.8","DOIUrl":"https://doi.org/10.15233/gfz.2021.38.8","url":null,"abstract":"This paper is devoted to applications of the “Extremum” loss simulation system to two damaging earthquakes which occurred in Croatia in 2020. We provide a calibration procedure of mathematical models used for shaking intensity simulation. The regional macroseismic field parameters, such as the coefficients in the macroseismic field equation; the ratio between the longer (b) and the shorter (a) axes of the higher elliptical isoseismals (the flattening ratio k); the angle that specifies the orientation of the macroseismic field, in particular, the azimuth of the longer axis in the isoseismal ellipse, were all based on extensive macroseismic data acquired for the Balkan region and on the data for an analogous area with similar seismotectonic parameters in the Caucasus. We obtained a fairly good consistency between the results of simulation applied to the impact of the 2020 Croatia earthquakes and observations, confirming that the calibration of the macroseismic model by the Extremum system was both reasonable and effective for enhancing reliability for real time loss estimation.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47599858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Following the 22 March 2020 ML 5.5 earthquake near Zagreb, Croatia, the citizens became increasingly interested in earthquakes and the multitude of simultaneous visitors caused the webpage with Croatian Seismological Survey reports on earthquakes to crash. To remedy the situation, seismologists used social network accounts to provide information, using the opportunity to educate the citizens on basic concepts of seismology, earthquake preparedness and the occurring seismic sequence. Citizens’ feedback was useful to improve the communication, but required extensive moderation. In July 2020, three seismologists from the Department of Geophysics, Faculty of Science, University of Zagreb, one from the Slovenian Environment Agency, and a psychologist from the Croatian Catholic University conducted a poll to find out which sources of information citizens mostly use, their knowledge about earthquakes, and the level of fear they were experiencing due to the earthquakes. Most respondents relied on institutional sources of information and their knowledge on different aspects of earthquake preparedness increased relatively compared to the time before the earthquake. The majority of respondents was extremely worried on the day of the mainshock, predominantly because they were concerned of a possible stronger event, their safety and the safety of their close ones.
{"title":"The public response and educational outreach through social media after the Zagreb earthquake of 22 March 2020","authors":"M. Mustać, I. Dasović, Helena Latečki, I. Cecić","doi":"10.15233/gfz.2021.38.7","DOIUrl":"https://doi.org/10.15233/gfz.2021.38.7","url":null,"abstract":"Following the 22 March 2020 ML 5.5 earthquake near Zagreb, Croatia, the citizens became increasingly interested in earthquakes and the multitude of simultaneous visitors caused the webpage with Croatian Seismological Survey reports on earthquakes to crash. To remedy the situation, seismologists used social network accounts to provide information, using the opportunity to educate the citizens on basic concepts of seismology, earthquake preparedness and the occurring seismic sequence. Citizens’ feedback was useful to improve the communication, but required extensive moderation. In July 2020, three seismologists from the Department of Geophysics, Faculty of Science, University of Zagreb, one from the Slovenian Environment Agency, and a psychologist from the Croatian Catholic University conducted a poll to find out which sources of information citizens mostly use, their knowledge about earthquakes, and the level of fear they were experiencing due to the earthquakes. Most respondents relied on institutional sources of information and their knowledge on different aspects of earthquake preparedness increased relatively compared to the time before the earthquake. The majority of respondents was extremely worried on the day of the mainshock, predominantly because they were concerned of a possible stronger event, their safety and the safety of their close ones.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41745440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The CROPOS’s ZAGR stations, one of 33 stations of the Croatian permanent GNSS (Global Navigation Satellite System) network CROPOS (Croatian Positioning System), is located in Zagreb’s city centre. For the first time, motion of one of the CROPOS stations (the ZAGR station) during an earthquake shake (the Zagreb 2020 ML5.5) was analysed by the PPK (Post-Processed Kinematic) method using all available GNSS signals (GPS – Global Positioning System, GLONASS – GLObalnaya NAvigatsionnaya Sputnikovaya Sistem, Galileo, Bei-Dou) and seismologically interpreted. The ZAGR station is situated about 9 km to the south-southeast of the earthquake’s epicentre. The analysis showed that the station’s movements, i.e. combined surface and building motion, during the shake was far above the noise level and enabled the assessment of the station’s kinematics: movements in the range of approx. 13 cm in direction north–south (N–S) and approx. 6 cm in direction east–west (E–W). However, movements in the vertical direction were slightly above the noise level. Even though the ZAGR station kinematic behaviour was pronounced, no permanent displacement was identified. The seismological analysis showed that the ZAGR station recorded the onset of the SV-waves on the N–S component, surface waves on the N–S (predominantly Rayleigh waves) and E–W (mainly Love waves) components. The resolution of 1 s of the results of the PPK method have enabled a thorough analysis of the ZAGR station kinematics and pointed out the usefulness of the method in earthquake observations.
{"title":"Geodetic and seismological analysis of the CROPOS ZAGR station kinematics during the Zagreb 2020 ML 5.5 earthquake","authors":"D. Sugar, Z. Bacic, I. Dasović","doi":"10.15233/gfz.2021.38.10","DOIUrl":"https://doi.org/10.15233/gfz.2021.38.10","url":null,"abstract":"The CROPOS’s ZAGR stations, one of 33 stations of the Croatian permanent GNSS (Global Navigation Satellite System) network CROPOS (Croatian Positioning System), is located in Zagreb’s city centre. For the first time, motion of one of the CROPOS stations (the ZAGR station) during an earthquake shake (the Zagreb 2020 ML5.5) was analysed by the PPK (Post-Processed Kinematic) method using all available GNSS signals (GPS – Global Positioning System, GLONASS – GLObalnaya NAvigatsionnaya Sputnikovaya Sistem, Galileo, Bei-Dou) and seismologically interpreted. The ZAGR station is situated about 9 km to the south-southeast of the earthquake’s epicentre. The analysis showed that the station’s movements, i.e. combined surface and building motion, during the shake was far above the noise level and enabled the assessment of the station’s kinematics: movements in the range of approx. 13 cm in direction north–south (N–S) and approx. 6 cm in direction east–west (E–W). However, movements in the vertical direction were slightly above the noise level. Even though the ZAGR station kinematic behaviour was pronounced, no permanent displacement was identified. The seismological analysis showed that the ZAGR station recorded the onset of the SV-waves on the N–S component, surface waves on the N–S (predominantly Rayleigh waves) and E–W (mainly Love waves) components. The resolution of 1 s of the results of the PPK method have enabled a thorough analysis of the ZAGR station kinematics and pointed out the usefulness of the method in earthquake observations.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47496603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Although strong and damaging earthquakes have hit Zagreb in the past, the 22 March 2020 earthquake (Mw 5.4) is the first one that was recorded by a modern digital local seismic network, and which could be analysed not only by macroseismic methods, but also by microseismic ones. Herewith we used the 3003 carefully analysed and located events from the first year of the aftershock sequence to learn more about the aftershock rate decay, their magnitude distribution, focal mechanisms and hypocentral locations. The aftershock activity rate was found to closely follow the modified Omori law, and fault-plane solutions for 10 events indicated prevailing pure-reverse faulting. Our analyses suggest that the reverse North Medvednica boundary fault (NMBF) was the causative fault, as it fits with the focal mechanisms and with the geometry of aftershock locations. The epicentral area was of a triangular shape with the mainshock in one vertex, and the opposite side of the triangle lying parallel to the surface trace of the NMBF. The hypocentres of aftershocks were predominantly located in the hanging wall of the fault. No surface break was observed, so the rupture is assumed to be buried. These facts were interpreted as a combination of the effect of conservation of mass (seismic flow) requiring some fault-parallel stress redistribution and transfer of material, and the fault loading and activation in the compressive environment controlled by the stress partition at the brittle-ductile transition zone within the crust. The later process involves compression within the hanging wall during the interseismic stage when the fault segment in the brittle crust is locked, followed by sudden dilatation during the rupture phase.
{"title":"Properties of the Zagreb 22 March 2020 earthquake sequence","authors":"M. Herak, D. Herak, Niksa Orlic","doi":"10.15233/gfz.2021.38.6","DOIUrl":"https://doi.org/10.15233/gfz.2021.38.6","url":null,"abstract":"Although strong and damaging earthquakes have hit Zagreb in the past, the 22 March 2020 earthquake (Mw 5.4) is the first one that was recorded by a modern digital local seismic network, and which could be analysed not only by macroseismic methods, but also by microseismic ones. Herewith we used the 3003 carefully analysed and located events from the first year of the aftershock sequence to learn more about the aftershock rate decay, their magnitude distribution, focal mechanisms and hypocentral locations. The aftershock activity rate was found to closely follow the modified Omori law, and fault-plane solutions for 10 events indicated prevailing pure-reverse faulting. Our analyses suggest that the reverse North Medvednica boundary fault (NMBF) was the causative fault, as it fits with the focal mechanisms and with the geometry of aftershock locations.\u0000The epicentral area was of a triangular shape with the mainshock in one vertex, and the opposite side of the triangle lying parallel to the surface trace of the NMBF. The hypocentres of aftershocks were predominantly located in the hanging wall of the fault. No surface break was observed, so the rupture is assumed to be buried. These facts were interpreted as a combination of the effect of conservation of mass (seismic flow) requiring some fault-parallel stress redistribution and transfer of material, and the fault loading and activation in the compressive environment controlled by the stress partition at the brittle-ductile transition zone within the crust. The later process involves compression within the hanging wall during the interseismic stage when the fault segment in the brittle crust is locked, followed by sudden dilatation during the rupture phase.","PeriodicalId":50419,"journal":{"name":"Geofizika","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41413884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jakov Stanislav Uglešić, S. Markušić, B. Padovan, D. Stanko
The 22 March 2020 Zagreb ML 5.5 earthquake ground shaking resulted in damage to buildings and infrastructure. The most affected buildings were older and cultural heritage buildings (built before 1963) in the old city centre with significant damage extent in the epicentral zone (southeastern foothills of Medvednica Mt.). This study presents site response analysis on the realistic site profiles from the epicentre towards the accelerometric stations QUHS and QARH and comparison with strong motion data recorded during the Zagreb 2020 earthquake. Semi-empirical estimation of the ground motion amplification (i.e., peak ground acceleration at surface) showed that modelled and recorded values are comparable. Moreover, we present 2D model of peak ground acceleration at surface (PGAsurf ) variation for the superimposed site profile from the epicentre towards two accelerometric stations. Ground motion amplification for the Zagreb ML 5.5 earthquake scenario showed that PGAsurf is larger by a factor of 2 than the bedrock value (approx. 0.35 g in the epicentre and 0.20 g on the 12 km distant accelerometric station). This study is a contribution to better understanding of the Zagreb ML 5.5 earthquake effects and significance of local site effects in the damage extent, something that combined with older and heritage buildings resulted in high economic consequences. Therefore, it is important that site-specific ground motion simulation and seismic microzonation of the Zagreb continues with installation of an accelerometric array. This is very important for earthquake retrofitting and resilience of the low, mid- and high-rise buildings with particular care of cultural and historical buildings as well for the further urban planning.
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