Macroseismic Observations Research Articles

2 February 1816, an Overlooked North Atlantic M 8 Earthquake

AbstractThe 2 February 1816 North Atlantic earthquake is virtually unknown to the international scientific community, and the few existing studies—solely based on two or three macroseismic intensities—pointed to a magnitude near 7 and a location at the eastern end of the Gloria fault in the Azores-Gibraltar Fracture Zone (AGFZ). Through careful search, we discovered more than 40 independent macroseismic observations and were able to estimate a total of 26 values of intensity, covering a wide geographical area (Iberian Peninsula, Madeira, and Azores). To apply the Bakun and Wentworth (B&W) method to the macroseismic dataset, we also deduced intensity–distance attenuation equations for the three different Atlantic coasts. The B&W procedure enabled us to conclude that the 2 February 1816 earthquake had a moment magnitude of 8.6±0.3 at the 95% confidence level and an epicentral location of 37.8° N and 19.8° W, near the central part of the Gloria fault. These results place the event as the greatest known earthquake in the Gloria fault domain and as one of the greatest ever seismic events along the AGFZ, probably only surpassed by the 1755 Lisbon earthquake.

Comment on “Active Crustal Deformation in the Trans‐Mexican Volcanic Belt as Evidenced by Historical Earthquakes During the Last 450 Years” by G. Suárez et al.

Comment on “Active Crustal Deformation in the Trans‐Mexican Volcanic Belt as Evidenced by Historical Earthquakes During the Last 450 Years” by G. Suárez et al.

The 6 November 1774 MI 6 Bolaños Graben Earthquake (Southern Basin and Range Province, West-Central Mexico): Macroseismic Observations and Neotectonic Implications

AbstractThe continental part of west-central Mexico is characterized by the active extensional tectonic regimes of the Trans-Mexican volcanic belt and the adjacent southern Basin and Range Province. The deformation of the latter is distributed over several topographically very pronounced grabens and half-grabens (width 10–20 km, length ≤200 km; throw 1–2 km), including the Aguascalientes, Juchipila, Tlaltenango, and Bolaños grabens. Here, an A.D. 1774–1775 earthquake series in that area is documented based on numerous contemporary sources. The 6 November 1774 mainshock caused moderate-to-severe damage in several communities of the Bolaños graben, including the silver mining town of Bolaños, and moderate damage to communities in the Tlaltenango graben, such as the administrative center of Colotlán. Based on the macroseismic intensity distribution, the epicenter was in the Bolaños graben. The preferred magnitude of the mainshock is ∼6.0±0.5. No major historical earthquake had been reported previously from this region. Existing ground-shaking hazard models may, therefore, give a false sense of security.In the Bolaños graben, motion along the graben-bounding faults and the observed tilting of the graben shoulders has to be mostly younger than the 19.9 Ma age of the youngest basalt of the graben-shoulder stratigraphy. Its correlation across the western master fault indicates a 1300 m throw and a vertical long-term slip rate of 0.07 mm/yr. The observations of alluvial fan deposits juxtaposed against the footwall ignimbrites along the western master fault of the Bolaños graben, the displacement of alluvial fan deposits along secondary faults within the graben, and the existence of hot springs along the western boundary fault all are indicative of active deformation, and so is evidently the A.D. 1774 earthquake.

Source parameters of the 1926 and 1927 Jersey earthquakes from historical, instrumental, and macroseismic data

English Channel Islands are located off Normandy coast of France within an intraplate area not associated with high seismicity rate and active tectonics. However, in July 1926 a damaging and well-documented earthquake occurred there, followed by a strongly felt event in February 1927. In this paper, we reprocess macroseismic observations, analog seismograms and bulletin data in order to re-appraise the location and magnitude of these two earthquakes. We find that the macroseismic epicentre of the 1926 Jersey earthquake is shifted to the East when compared with the location offshore South of Jersey given in both the French database SisFrance and the recent French catalog FCAT-17. Arrival-times from published data, together with our own onset-time readings, are processed in order to obtain probabilistic hypocentral locations. The maximum-likelihood instrumental epicentre of the 1926 event is located about 15 km East of Jersey Island (49.20°N, 1.82°W). This epicentre is well constrained within a 10 km radius area. The location of the 1927 epicentre is slightly south of Jersey, at a location similar to that of SisFrance, but this latter epicentre is less constrained as fewer observations are available (the Probability Density Function for the 1927 epicentre is relatively “diluted”). Focal depth remains very poorly determined for both the 1926 and 1927 events. Analysis of historical seismograms is also performed in order to determine both surface-wave and moment magnitudes, MS and MW. We find MS = 5.6 ± 0.2 for the 1926 event and MS = 5.0 for the 1927 event. Waveform fitting of some of the highest quality seismograms of the 1926 event gives us MW in the range [5.0, 5.5], depending on the chosen focal depth and focal mechanism. The 1927 Jersey earthquake is expected with an intensity magnitude MI about 0.6 smaller.

Seismic activity on the territory of Slovakia in 2018

Abstract The National Network of Seismic Stations of Slovakia (NNSS) consists of eight short period and five broadband permanent seismic stations and a data centre located at the Earth Science Institute of the Slovak Academy of Sciences (ESI SAS). The NNSS recorded and detected 11704 seismic events from all epicentral distances in 2018. Totally 86 earthquakes originated in the territory of Slovakia in 2018. This paper provides basic information on the configuration of the NNSS, routine data processing, seismic activity on the territory of Slovakia in 2018 as well as macroseismic observations collected in 2018.

ТУЯБУГУЗСКОЕЗЕМЛЕТРЯСЕНИЕ 25 мая 2013 г. сКР=14.1, MS=5.2, I0=7 (Приташкентский район, Узбекистан)

The results of instrumental and macroseismic observations of the Tuyabuguz earthquake on May 24, 2013, with КР=14.1, МS=5.2, I0=7 (MSK-64) are presented. The earthquake occurred 35 km southwest of Tashkent and was felt up in many settlements of Uzbekistan. The isoseismal map is given. Correspondence between the intensity of the earthquake manifestation and the regional macroseismic field equation is shown. Geological and geophysical conditions in the epicentral zone are described. The seismicity of the observation area is reviewed. The focal area of the Tuyabuguz earthquake is located in the seismically active zone, where strong historical and instrumentally recorded events occurred with intensity I=7–8 point.

Testing and Developing the Macroseismic Intensity Attenuation Relationships for the Vrancea (Romania) Crustal Earthquakes

A correct seismic hazard assessment and intensity-based shake maps of a seismic zone depend on the determination of parameters that emphasize the distribution and the macroseismic intensity attenuation for that seismogenic zone. Due to the reduced number of strong ground motion records, macroseismic intensity information available for previous earthquakes which have occurred in studied area were the only source of information utilized for developing attenuation relationship for that zone. The aim of this paper is to test the existing equations published for various crustal seismic sources and develop a new macroseismic intensity attenuation law for the Vrancea crustal seismic source. The Vrancea crustal seismogenic zone had experienced moderate earthquakes in the past with magnitudes which did not exceed 5.9 [1] and macroseismic maralps had been constructed by various authors for these earthquakes representing intensity pattern and decrease of this parameter with distance on different azimuths. Some of the selected attenuation laws were tested for different values of epicentral intensity and with reference to eight directions. The input data consist of macroseismic intensities collected for 4 small and moderate earthquakes (Mw ≥ 3.9) that had occurred during the last hundred years with epicentral/maximum intensity in the range IV to VI MSK degrees. The seismic events used to verify the attenuation laws were selected based on the magnitude and number of macroseismic observations collected for each event. Using this data, attenuation relationships of macroseismic intensity with distance will be tested and modified. The deduced attenuation equation might be used for rapid intensity assessment of the potential future earthquakes occurred in this seismic zone.

Seismic activity on the territory of Slovakia in 2017

Abstract The National Network of Seismic Stations of Slovakia (NNSS) consists of eight short period and five broadband permanent seismic stations and a data centre located at the Earth Science Institute of the Slovak Academy of Sciences (ESI SAS). The NNSS recorded and detected 10 719 seismic events from all epicentral distances in 2017. Totally 73 earthquakes originated in the territory of Slovakia in 2017. This paper provides basic information on the configuration of the NNSS, routine data processing, seismic activity on the territory of Slovakia in 2017 as well as macroseismic observations collected in 2017.

Seismic activity on the territory of Slovakia in 2016

Abstract The National Network of Seismic Stations of Slovakia (NNSS) consists of eight short period and five broadband permanent seismic stations and a data centre located at the Earth Science Institute of the Slovak Academy of Sciences (ESI SAS). The NNSS recorded and detected 10888 seismic events from all epicentral distances in 2016. Totally 87 earthquakes originated in the territory of Slovakia in 2016. This paper provides basic information on the configuration of the NNSS, routine data processing, seismic activity on the territory of Slovakia in 2016 as well as macroseismic observations collected in 2016.

Bayesian Estimation of Macroseismic Intensity from Post-Earthquake Rapid Damage Mapping

The seismological community acknowledges the essential contribution of macroseismic assessment to the compilation of the seismic catalogs used for seismic hazard assessment. Furthermore, macroseismic observations are routinely employed by civil protection authorities in the aftermath of damaging events to improve their decision making. In this paper, we describe a novel methodology for the rapid, probabilistic estimation of macroseismic intensity in the epicentral area of a major event according to the European Macroseismic scale. The methodology includes mobile mapping and a collaborative online platform for rapid post earthquake reconnaissance. A Bayesian scheme is proposed to integrate direct damage observations and prior information, allowing consideration of ancillary data and expert judgment. According to a feasibility study carried out in the area affected by the 2016 Amatrice (Central Italy) earthquake, the proposed methodology should provide a reliable estimation of intensity, efficiently integrating further post earthquake building damage surveys.

Definition of the death of seismic events by using digital channel data of the Main center of special control and foreign seismic stations

Among the main parameters of the source of the seismic event, the depth of the hypocentre is of greatest interest, which, as a rule, is determined with the least accuracy. The knowledge of the exact spatial position of the earthquake foci makes it possible to reveal their connection with the features of the structure of the earth’s crust, primarily with active faults. The solution of these problems is primarily ensured by the use of observational data obtained with the help of local, regional or global networks of digital seismic stations, as well as by improving computer technologies and methods of processing digital seismic data. To determine the parameters of low-energy seismic events, the epicenters of which are located within the platform part of the territory of Ukraine, it is expedient to use the data of instrumental observations obtained with the help of the regional network of digital seismic stations of the Main Center for Special Control (MCSK) of the State Space Agency of Ukraine. To increase the accuracy of localization of seismic events, it is necessary, on the one hand, to significantly expand the network of seismic observations, and on the other, to improve the methods for determining the basic parameters of earthquakes. The article analyzes the basic methods for determining the depths of the hypocenters of seismic events. The program-mathematical support allowing to make the depths of the earthquake foci by records of reflected waves and from the data of macroseismic observations is considered. To estimate the depth of seismic sources from the data of digital seismic channels of the MCSK and foreign seismic stations, the amplitude-frequency characteristics of which are available in the «Geotool», a specialized program «Assessment of depth» has been developed. A number of foreign and domestic seismic stations, most suitable for clarifying the depths of hypocenters of earthquakes from the area of the Vranch Mountains, has been determined. A method for determining the depth of an earthquake source from the area of the Vranch Mountains using data from digital seismic stations located at distances of 20—40 km from the center of a seismically active zone is proposed.

On the Lefkas (Ionian Sea) November 17, 2015 Mw=6.5 Earthquake Macroseismic Effects

ABSTRACT We exploit macroseismic observations and instrumental data aiming at explaining the effects of the 17th November 2015 Mw=6.5 earthquake, occurred beneath the southwestern peninsula of Lefkas Island (Ionian Sea) causing two casualties, major geo-environmental and slight-to-moderate structural effects. The spatial distribution of the structural damage of the local building stock is well correlated with the deformation pattern deduced from satellite geodesy, it appears though considerably low with respect to the ground deformation. Comparison with the previous strong earthquake on 14.8.2003 with Mw=6.2 occurred about 20 km to the north, shows that structural damage was significantly lower during the recent quake and also manifests good behaviour of the local buildings. This is partly explained by the characteristics of the ground motion and primarily explained by the unique concepts applied to the non-engineered buildings of Lefkas to resist ground motions.

DEVELOPING SEISMIC INTENSITY MAPS FROM TWITTER DATA; THE CASE STUDY OF LESVOS, GREECE 2017 EARTHQUAKE: ASSESSMENTS, IMPROVEMENTS AND ENRICHMENTS ON THE METHODOLOGY

Abstract. This article presents an effort to validate and further improve a previously published innovative approach for drawing macroseismic intensity maps from data extracted from sources of volunteered geographic information (VGI). Our approach involves classification of macroseismic observations (extracted from social media sources) to values of the EMS 98 intensity scale, leading to the drawing of isoseismal maps. The earthquake of June 12th, 2017 (Mw 6.3) that occurred off the south coast of Lesvos Island, Greece, was used as a case study; its main shock was located at depth of about 13 km. This specific event, which claimed the life of a woman and caused at least 15 injuries due to collapsing buildings and falling debris (mainly in the town of Vrissa), was chosen for the specific geomorphological characteristics of the meizoseismal area, time of occurrence and distribution of damage. Twitter was chosen as a VGI source mostly for reasons of consistency with the original published work, generating comparable findings that can be assessed more readily to facilitate further development of the methodology. Results of the dataset analysis include the drawing of the isoseismal maps from Tweets published within different time periods (6 h, 12 h, 24 h, 48 h); and the identification of various text patterns regarding the evaluation of the macroseismic observations that result into intensity values. The present work offers additional empirical evidence regarding the validity of the methodology presented in the scientific literature, and further enriches it by providing additional text patterns and specific improvements related to the classification of the information in certain values of seismic intensity. Assessment of the results is enriched by the progress that has been noted in the field and has been presented in the international scientific literature since 2016.

The 2 October 1847 MI 5.7 Chapala Graben Triggered Earthquake (Trans‐Mexican Volcanic Belt, West‐Central Mexico): Macroseismic Observations and Hazard Implications

Research Article| November 01, 2017 The 2 October 1847 MI 5.7 Chapala Graben Triggered Earthquake (Trans‐Mexican Volcanic Belt, West‐Central Mexico): Macroseismic Observations and Hazard Implications Max Suter Max Suter aInstituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Hermosillo, Sonora, Mexico, sutermax@alumnibasel.ch Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2018) 89 (1): 35–46. https://doi.org/10.1785/0220170101 Article history first online: 01 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Max Suter; The 2 October 1847 MI 5.7 Chapala Graben Triggered Earthquake (Trans‐Mexican Volcanic Belt, West‐Central Mexico): Macroseismic Observations and Hazard Implications. Seismological Research Letters 2017;; 89 (1): 35–46. doi: https://doi.org/10.1785/0220170101 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT The Trans‐Mexican volcanic belt is an active continental volcanic arc related to subduction along the Middle America trench and characterized by several major arc‐parallel middle Miocene—Holocene lake basins formed by normal faults and related crustal seismicity. The Chapala graben, the largest of these basins in the western part of the Trans‐Mexican volcanic belt, is 115 km long and up to 30 km wide. Here, I document a 2 October 1847 earthquake with intensity magnitude MI of 5.7±0.4 that was locally devastating on the northern graben shoulder. It razed the villages of Poncitlán and Ocotlán in the state of Jalisco, where at least 58 persons perished. The macroseismic observations for this historical event and the elevated background seismicity indicate that the Chapala graben is active and poses a major ground‐shaking hazard to the nearby metropolitan areas of Ocotlán and Guadalajara. No historical earthquake had been previously documented from the Chapala graben, which was believed to be tectonically inactive. Furthermore, the 2 October 1847 event was not recognized as a crustal earthquake. In earthquake catalogs, the devastation at Ocotlán is aggregated with the damage caused on the same day, only two hours earlier, in the Colima region by a subduction‐zone earthquake that was devastating in Tecomán and Colima and caused minor damage in Mexico City, and which likely triggered dynamically the Chapala graben earthquake. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fault parameters and macroseismic observations of the May 10, 1997 Ardekul-Ghaen earthquake

The Ardekul (Zirkuh) earthquake (May 10, 1997) is the largest recent earthquake that occurred in the Ardekul-Ghaen region of Eastern Iran. The greatest destruction was concentrated around Ardekul, Haji-Abad, Esfargh, Pishbar, Bashiran, Abiz-Qadim, and Fakhr-Abad (completely destroyed). The total surface fault rupture was about 125 km with the longest un-interrupted segment in the south of the region. The maximum horizontal and vertical displacements were reported in Korizan and Bohn-Abad with about 210 and 70 cm, respectively; moreover, other building damages and environmental effects were also reported for this earthquake. In this study, the intensity value XI on the European Macroseismic Scale (EMS) and Environmental Seismic Intensity (ESI) scale was selected for this earthquake according to the maximum effects on macroseismic data points affected by this earthquake. Then, according to its macroseismic data points of this earthquake and Boxer code, some macroseismic parameters including magnitude, location, source dimension, and orientation of this earthquake were also estimated at 7.3, 33.52° N–59.99° E, ~ 75 km long and ~ 21 km wide, and ~ 152°, respectively. As the estimated macroseismic parameters are consistent with the instrumental ones (Global Centroid Moment Tensor (GCMT) location and magnitude equal 33.58° N–60.02° E, and 7.2, respectively), this method and dataset are suggested not only for other instrumental earthquakes, but also for historical events.

Inferring Earthquake Ground‐Motion Fields with Bayesian Networks

Bayesian Networks (BNs) have the ability to perform inference on uncertain variables given evidence on observed quantities, which makes them relevant mathematical tools for the updating of ground-motion fields based on strong-motion records or macroseismic observations. Therefore the present article investigates the use of BN models of spatially correlated Gaussian random fields as an accurate and scalable method for the generation of ground-motion maps. The proposed BN model is based on continuous Gaussian variables, as opposed to discrete variables as in previous formulations, and it is built to account for cross-correlated ground-motion parameters as well as macroseismic observations. This approach is validated with respect to the analytical solution (i.e., conditional multivariate normal distributions) and it is also compared to the USGS ShakeMap method, thus demonstrating a better ability to model jointly the inter- and intra-event error terms of ground-motion models. The scalability of the approach, i.e. its capacity to be applied to large grids, is ensured by a grid sub-division strategy, which appears to be computationally efficient and accurate within an error rate of a fraction of percent. Finally, the BN implementation is demonstrated on a real-world example (the Mw 6.2 Kumamoto, Japan, 2016 foreshock), where vector-valued shake-maps of cross-correlated intensity measures are generated, along with the integration of macroseismic observations.

Historical seismogram reproductions for the source parameters determination of the 1902, Atushi (Kashgar) earthquake

The majority of original seismograms recorded at the very beginning of instrumental seismology (the early 1900s) did not survive till present. However, a number of books, bulletins, and catalogs were published including the seismogram reproductions of some, particularly interesting earthquakes. In case these reproductions contain the time and amplitude scales, they can be successfully analyzed the same way as the original records. Information about the Atushi (Kashgar) earthquake, which occurred on August 22, 1902, is very limited. We could not find any original seismograms for this earthquake, but 12 seismograms from 6 seismic stations were printed as example records in different books. These data in combination with macroseismic observations and different bulletins information published for this earthquake were used to determine the source parameters of the earthquake. The earthquake epicenter was relocated at 39.87° N and 76.42° E with the hypocenter depth of about 18 km. We could further determine magnitudes m B = 7.7 ± 0.3, M S = 7.8 ± 0.4, M W = 7.7 ± 0.3 and the focal mechanism of the earthquake with strike/dip/rake − 260°± 20/30°± 10/90°± 10. This study confirms that the earthquake likely had a smaller magnitude than previously reported (M8.3). The focal mechanism indicates dominant thrust faulting, which is in a good agreement with presumably responsible Tuotegongbaizi-Aerpaleike northward dipping thrust fault kinematic, described in previous studies.

Comparison of PSH results with historical macroseismic observations at different scales. Part 2: application to South-East France

The companion paper by Rota and Rosti (Bull Earthq Eng, 2017) illustrates a methodology for comparing PSH results with historical macroseismic observations at different scales, in terms of mean damage. This paper presents examples of application of the methodology, at the different considered scales, to the South-East quarter of France. This moderate seismicity region is characterised by a long history of civilization, which makes macroseismic observations available for a long time span, although they are highly approximated measures of the seismic action and they are affected by significant uncertainties. The first scale of application presented is at a single site, i.e. the city of Annecy. This example shows that, despite the seismic history of this city is characterised by a significant number of macroseismic observations spanning over a long time period, they mostly consist of very low intensity values and hence the comparison at a single site is not very meaningful. Therefore, the comparison is carried out on a set of seven aggregated sites, well distributed in the region of interest, providing interesting results and suggesting the opportunity of extending the comparison at an even larger scale. The comparison at the regional scale also allows some interesting observations, although it is obviously able to only provide general (average) indications on the PSH results. These comparisons were aimed at showing the applicability of the proposed methodology, pointing out advantages and drawbacks of the different application scales.

Depths of Earthquakes in South Africa

ABSTRACT Historically, hypocentral depths of earthquakes in South Africa are not well documented from instrumentally determined parameters. We, therefore, investigated a concise number of earthquakes in South Africa over a broad geographical region. We reviewed the hypocentral depths of instrumentally recorded tectonic earthquakes in South Africa through synthetic waveform modeling and through a separate study using multiple phase arrivals. The resulting depths of earthquakes in South Africa occur at shallow crustal depths. It is further shown that uncertainty in focal depth is higher using the multiphase method in comparison with the regional depth‐phase modeling method. Methodology for determining focal depth from macroseismic observations is introduced in this article; however, poor coverage of intensity observations within the epicentral area limited the reliability of this method. Therefore, the study of hypocentral depths inferred from macroseismic observations was inconclusive, resulting from limited intensity data. Shallow depths are, however, inferred from the spatial patterns that do not exhibit the characteristic intensity patterns of deep earthquakes. It was noted during this study that the majority of events display the distinguishable isoseismal pattern of shallow earthquakes, whereas only a selected number of earthquakes exhibit spatial patterns expected of deeper crustal events. The present study did not find conclusive evidence of earthquakes occurring in the lower crust of South Africa from the limited number of earthquakes considered, which therefore indicates a unimodal depth distribution of earthquakes in the upper crust between the depths of 3 and 20 km. This observation contradicts reports in internationally published earthquake catalogs that indicate deeper earthquakes for individual events, for example, the M w ∼6.2 1969 Ceres earthquake.

Comparison of PSH results with historical macroseismic observations at different scales. Part 1: methodology

The need for verifying and/or validating the results of probabilistic seismic hazard studies has become evident, despite the absence of generally accepted methods for judging such results. This paper proposes a methodology for comparing the results of PSH with historical macroseismic observations, at different scale levels. The selected metric of the comparison is the mean damage, i.e. the average annually expected damage. Hence, a procedure for converting macroseismic observations and PGA levels, for which PSH estimates are provided, into mean damage values is first presented. The procedure is based on the macroseismic method for converting intensities into mean damage values, whereas it takes advantage of fragility curves (representative of the seismic vulnerability of the building stock at the time of historical observations) to transform the rates of occurrence of PGA values into the equivalent quantity in terms of mean damage. A methodology for site-specific comparison is first outlined. To overcome some of the limitations of the comparison at a single site, two procedures for aggregating several sites by sampling in space are then presented, with the aim of enlarging the available macroseismic dataset. Finally, a procedure for the comparison at the regional level is discussed. Applications of the proposed methodologies will be discussed in a companion paper (Rosti and Rota in Bull Earthq Eng, 2017).