Epicentral Intensity Research Articles

A decade of seismicity in metropolitan France (2010–2019): the CEA/LDG methodologies and observations

We summarize ten years of the French seismicity recorded by the Geophysical and Detection Laboratory (LDG) of the French Alternative Energies and Atomic Energy Commission (CEA) network from 2010 to 2019. During this period, 25 265 natural earthquakes were detected by the LDG and located within metropolitan France and its immediate vicinity. This seismicity contributes to more than 47% of the natural earthquakes instrumentally recorded since 1962 (mainly due to the improvement of network capacity), and includes about 28% of the most significant earthquakes with a magnitude ML ≥ 4.0. Recent seismic events therefore significantly expand the available national catalogues. The spatial distribution of 2010–2019 earthquakes is broadly similar to the previously recorded instrumental pattern of seismicity, with most of the seismic activity concentrated in the French Alps, the Pyrenees, Brittany, the upper Rhine Graben and the Central Massif. A large part of the seismic activity is related to individual events. The largest earthquakes of the last ten years include the November 11, 2019 Le Teil earthquake with ML 5.4 and epicentral intensity VII–VIII, which occurred in the Rhone valley; the April 28, 2016 La Rochelle earthquake with ML 5.1 and epicentral intensity V, which occurred at the southernmost extremity of the Armorican Massif in the vicinity of the Oléron island; and the April 7, 2014 Barcelonnette earthquake with ML 5.1 and epicentral intensity V–VI, which occurred in the Ubaye valley in the Alps. In 2019, two other moderate earthquakes of ML 5.1 and ML 4.9 stroke the western part of France, in Charente-Maritime and Maine-et-Loire departments, respectively. The recent moderate earthquake occurrences and the large number of small earthquakes recorded give both the potential to revise some regional historical events and to determine more robust frequency-magnitude distributions, which are critical for seismic hazard assessment but complex due to low seismicity rates in France. The LDG seismic network installed since the early 1960s also allows a better characterization of the temporal structure of seismicity, partly diffused and in the form of mainshock-aftershocks sequences or transient swarms. These aspects are important in order to lower the uncertainties associated to seismogenic sources and improve the models in seismic hazard assessment for metropolitan France.

Photographic Reportage on the Rebuilding after the Irpinia-Basilicata 1980 Earthquake (Southern Italy)

This paper aims to present, through a photographic reportage, the current state of rebuilding of the most devastated villages by the earthquake that hit the Southern Italy on 23 November 1980, in Irpinia-Basilicata. The earthquake was characterized by magnitude Ml = 6.9 and epicentral intensity I0 = X MCS. It was felt throughout Italy with the epicenter in the Southern Apennines, between the regions of Campania and Basilicata that were the most damaged areas. About 800 localities were serious damaged; 7,500 houses were completely destroyed and 27,500 seriously damaged. The photographic survey has been done in 23 towns during the last five years: Castelnuovo di Conza, Conza della Campania, Laviano, Lioni, Santomenna, Sant’Angelo dei Lombardi, Balvano, Caposele, Calabritto and the hamlet of Quaglietta, San Mango sul Calore, San Michele di Serino, Pescopagano, Guardia dei Lombardi, Torella dei Lombardi, Colliano, Romagnano al Monte, Salvitelle, Senerchia, Teora, Bisaccia, Calitri and Avellino. Forty years after the 1980 earthquake, the photographs show villages almost completely rebuilt with modern techniques where reinforced concrete prevails. Only in few instances, the reconstruction was carried out trying to recover the pre-existing building heritage, without changing the original urban planning, or modifying it. We argue that this photography collection allows to assess the real understanding of the geological information for urban planning after a major destructive seismic event. Even more than this, documenting the rebuilding process in a large epicentral area reveals the human legacy to the natural landscape, and our ability, or failure, to properly interpret the environmental fate of a site.

A real-time prediction model for macroseismic intensity in China

The macroseismic intensity spatial distribution is an important input for most rapid loss modeling and emergency work. Data from a total of 175 earthquakes (Ms ≥ 5.0) in China from 1966 to 2014 were collected, and the rapid assessment method of macroseismic intensity distribution was studied. First, simple relationships among the epicentral intensity, magnitude, and focal depth were established. A greater amount of database is used in this study than that in a previous work (Fu and Liu in Sci R 4(5): 350-354 (1960), Mei in Chin J Geophys 9(1): 1–18 (1960), and Yan et al. in Sci Chin 11: 1050-1058 (1984)), and the studied earthquakes all occurred in the last 50 years, providing more accurate and uniform parameter information. As the seismic intensity-attenuation relationship is traditionally used to estimate the intensity distribution, the macroseismic intensity-attenuation relationship for mainland China was fitted by the earthquake data collected in this region. The deviation of the intensity assessment by the macroseismic intensity-attenuation relationship was examined for 43 earthquakes (Ms ≥ 6.0). In addition, seismic damage emergency assessment work requires the isoseismal lines to be constantly modified according to the updated information. Therefore, an improved ellipse intensity-attenuation model was proposed in this study, completed by the establishment of a semimajor axis and semiminor axis length matrix. Based on the initial value of the length matrix obtained by the regression of historical data and survey data from the site, the least mean squares (LMS) algorithm is used to revise the length matrix. In the end, the practicability of this method is verified by a case study of the Lijiang 7.0 earthquake.

Source analysis of the March 7, 2019 mathbf {M_L=4.0} Somogyszob, Hungary earthquake sequence

Between February 16 and April 5, 2019, a series of earthquakes took place around the village of Somogyszob, Somogy county, Hungary. The mainshock occurred on March 7 with a local magnitude M_L=4.0 and epicentral intensity of 5 on the EMS scale. The main event was preceded by four foreshocks and followed by four aftershocks. The largest foreshock (M_L=2.6) was also felt with maximum intensity of 4 EMS. This earthquake sequence is the first remarkable one in the region that was recorded by a significant number of high-quality broadband digital seismographs. We have estimated the hypocenters of the 9 earthquakes using the hypoDD multiple-event location algorithm. The events occurred in a tight region around the mainshock at around 13–14 km depth. For the main event, we obtained an average moment magnitude of M_w=3.75, source radii of r^P=509 m and r^S=400 m, and static stress drops of varDelta sigma ^P=1.19times 10^6 Pa and varDelta sigma ^S=4.00times 10^6 Pa from the analysis of displacement P- and S-wave spectra, respectively. The resulting spectral source parameters for the investigated events agree well with the results of earlier research. We have also shown that our recently developed probabilistic waveform inversion techniques applied in this study are suitable to retrieve the source mechanism for weak local earthquakes. We have successfully estimated the focal mechanism for the mainshock, a foreshock and an aftershock. Each earthquake was a thrust faulting event with a sub-horizontal P-axis pointing towards N-NE, coinciding with the general trend of the compressional stress field in the epicentral region.

Identification of the Seismogenic Structure in the Area of Chupa (North Karelia) and Parameterization of Paleoearthquakes in the Kandalaksha Graben Region

In the area of the village of Chupa, three isolated ranges of paleoseismic dislocations were revealed, marking a NW-trending linear seismogenic structure and a total length of more than 14 km . The dislocations are young tectonic ditches and fissures, mainly trending NW, mass displacements of blocks, including against the slope, disarrayed stones, and seismic landslides. Using the nature of the distribution of seismic dislocations for two areas, isoseismic maps were constructed, which made it possible to estimate the magnitudes of paleoseismic events using the macroseismic technique. They amounted to 3.7 and 2.9, respectively, with a focal depth of H ≤ 1 km under the assumption that each range corresponds to a local seismic source. The isolated character of the distribution of the identified ranges may be associated with another, more severe paleoearthquake, traces of which have been preserved mainly in elevated areas of the relief (above 80 m). In the Early Holocene, these sites were separate islands, since the formation conditions for dislocations were limited to subaquatic spaces. For this variant, M = 5.5 and H = 5 km were calculated; the age of the event is the Early Holocene. The results, taking into account data on the micrograben of the Great Salma Strait, indicate the periodic occurrence of coastal and mainland faults, subparallel to the axis of the Kandalaksha graben, as well as Holocene shallow-focus earthquakes of medium magnitude with an epicentral intensity up to I = VIII on the ESI-2007 scale. A catalog of postglacial paleoearthquakes of the Kandalaksha graben region has been compiled (5 events), which can be used to construct earthquake recurrence graphs. This will make it possible to substantially refine the seismic regime of this structure.

Developing the First Intensity Prediction Equation Based on the Environmental Scale Intensity: A Case Study from Strong Normal-Faulting Earthquakes in the Italian Apennines

AbstractEarthquakes produce effects on the built and natural environment, the severity of which decays with distance from the epicenter. Empirical relations describing the intensity attenuation with distance are fundamental for seismic hazard assessment and for deriving parameters for preinstrumental events. Seismic intensity is usually assigned based on damage to buildings and infrastructures; this can be challenging for intensity degrees higher than X or when macroseismic fields of multiple events close in time are overlapping. A complementary approach is the study of earthquake environmental effects (EEEs), which are used to assign intensity on the environmental scale intensity (ESI) scale. However, a quantitative comparison between the ESI and traditional scales, and an equation describing the ESI attenuation with distance are still lacking. Here, we analyze 14 historical and instrumental events (time window 1688–2016) in the central and southern Apennines (Italy), comparing ESI and Mercalli–Cancani–Sieberg (MCS) intensities. Our results show that ESI consistently provides higher intensity near the epicenter and the attenuation is steeper than MCS. We derive the first intensity prediction equation for the ESI scale, which computes local intensity as a function of distance and epicentral intensity value. We document that, in the near field, the MCS attenuation for shallow crustal events occurred in the twenty-first century is steeper than previous events, whereas the ESI attenuation shows a consistent behavior through time. This result questions the reliability of current empirical relations for the investigation of future events. We recommend including EEEs in intensity assignments because they can guarantee consistency through time and help in evaluating the spatial and temporal evolution of damage progression during seismic sequences, thus ultimately improving seismic risk assessment.

Reassessment of macroseismic intensities for two earthquakes in Colombia: Tumaco (1979, Mw = 8.1) and Armenia (1999, Mw = 6.1), using the ESI-2007 scale

A reassessment of the macroseismic intensities was performed for the Tumaco (December 12th, 1979, Mw = 8.1) and Armenia (January 25th, 1999, Mw = 6.1) earthquakes, based on the spatial distribution and quantification of dimensions of the surface geological and environmental effects in lists compiled from published documents. The newly constructed lists of 46 effects for the Tumaco earthquake (TE) and 123 effects for the Armenia earthquake (AE) were obtained by literature review and systematic searches of information in authoritative sources. The geological and environmental effects caused by the two earthquakes were then used to estimate seismic intensities and construct new isoseismal maps following the methodology of the ESI-2007 scale. Comparisons were made between the ESI-2007 isoseismal maps and those using data from traditional intensity scales (Modified Mercalli MM-31 and EMS-98) in terms of the percentage overlap between affected areas for each intensity level. For the AE, the newly computed intensities indicate epicentral intensity I0AE = 10 and the ESI-2007 intensities show best agreement with EMS-98 values, with a maximum of 54.2% overlap for intensities in the range 7–8. The new isoseismal maps for the TE indicate maximum intensity IMaxTE ~ I0TE = 11 and best agreement with MM-31 values, with a maximum of 48.8% overlap for intensities in the range 7–8. It is concluded that ESI-2007 intensities exhibit close agreement in most cases with MM-31 and EMS-98 values and provide new details for maximum intensities and the extent of affected areas which can be used in future plans of land use for earthquake-prone areas in Colombia.

TESTING THE MACROSEISMIC INTENSITY ATTENUATION RELATIONSHIPS FOR VRANCEA (ROMANIA) SUBCRUSTAL EARTHQUAKES IN RELATION WITH DAMS SITUATED IN EXTRA-CARPATHIAN AREA

The aim of the present paper is to test intensity attenuation relationships for subcrustal earthquakes occurred in Vrancea (Romania) seismogenic zone in relation with some important dams situated in extra-Carpathian area. During centuries, the Romanian territory has been shaken by strong earthquakes, most of them being centered within Vrancea Zone, which is situated at the bending area of the South-Eastern Carpathians. Most of the zones from extra-Carpathian area are affected by the subcrustal seismic events, where many hydro-technical structures exist, being also exposed to earthquakes action. A detailed analysis of the intensity attenuation laws developed for subcrustal seismic sources was performed using the most recent and complete intensity datasets. We use an extended and combined intensity data including historical and modern, qualitative and quantitative data, i.e. a number of 11 earthquakes occurred during the period 1738-2009 with epicentral/maximum intensities ranging from VII-X MSK degrees, and magnitude Mw from 5.4 to 7.9. All the input data used for testing are resulted after the reevaluation and evaluation of the macroseismic effects produced by the seismic events included in the present study (8697 IDP). The selected attenuation laws were tested for different values of epicentral intensity and with reference to twelve and twenty four azimuthal directions. Besides the testing of the relationships, isoseismal maps based on the selected attenuation laws were accomplished, associated to the biggest possible earthquake (worst scenario) for the Vrancea subcrustal zone, also highlighting the calculated intensities in the selected dam sites. Brief description of the study and used methods. Brief description of the study and used methods.

QUake-MD: Open-Source Code to Quantify Uncertainties in Magnitude–Depth Estimates of Earthquakes from Macroseismic Intensities

AbstractThis article presents a tool to quantify uncertainties in magnitude–depth (M-H) estimates for earthquakes associated with macroseismic intensity data. The tool is an open-source code written in Python and is named quantifying uncertainties in earthquakes’ magnitude and depth (QUake-MD). In QUake-MD, uncertainties are propagated from the individual intensity data point (IDP) to the final magnitude (M), depth (H), epicentral intensity (I0) solution. It also accounts for epistemic uncertainties associated with the use of different intensity prediction equations (IPEs). For each IPE, QUake-MD performs a sequential least-square inversion process to estimate the central M, H value. QUake-MD then explores the uncertainties around this central M, H solution by constructing a probability density function (PDF) constrained to be consistent with the range of plausible epicentral intensity I0, a plausible depth range, and IDP uncertainties. The resulting PDFs of all IPEs provided to QUake-MD are then stacked to obtain a final PDF of possible M, H, I0 solutions representative of both data quality and IPE epistemic uncertainties. This tool is geared toward end users who would like to grasp a more complete understanding of the uncertainties associated with historical earthquake parameters beyond the classical standard deviation values proposed today in parametric earthquake catalogs. We apply QUake-MD to two events of the SisFrance macroseismic database to illustrate the challenges involved in building realistic spaces of M, H, I0 solutions reflecting the quality of the data and the epistemic uncertainties in IPEs.

The Italian earthquake catalogue CPTI15

The parametric catalogue of Italian earthquakes CPTI15 (Catalogo Parametrico dei Terremoti Italiani) represents the latest of a 45-years-long tradition of earthquake catalogues for Italy, and a significant innovation with respect to its predecessors. CPTI15 combines all known information on significant Italian earthquakes of the period 1000–2017, balancing instrumental and macroseismic data. Although the compilation criteria are the same as in the previous CPTI11 version, released in 2012, the catalogue has been revised as concerns: the time coverage, extended to 2017; the associated macroseismic data, improved in quantity and quality; the considered instrumental data, new and/or updated; the energy thresholds, lowered to maximum or epicentral intensity 5 or magnitude 4.0 (instead of 5–6 and 4.5, respectively); the determination of parameters from macroseismic data, based on a new calibration; the instrumental magnitudes, resulting from new sets of data and new conversion relationships to Mw. The catalogue considers and harmonizes data of different types and origins, both macroseismic and instrumental. For all earthquakes, the magnitude is given in terms of true or proxy moment magnitude (Mw), with the related uncertainty. The compilation procedure rigorously implements data and methods published in peer-reviewed journals. All data and methods are clearly indicated in the catalogue, in order to guarantee the maximum transparency of the compilation procedures. As compared to previous CPTI releases, the final CPTI15 catalogue shows a frequency–magnitude distribution coherent with current Italian instrumental catalogues, making it suitable for statistical analysis of the time-space property of the Italian seismicity.

The Međimurje (Croatia) Earthquake of 1738

Abstract The 30 March 1738 earthquake with an epicenter near Čakovec in Međimurje (Croatia) is the largest known earthquake in the low-seismicity area that includes northernmost Croatia, northeastern Slovenia, southeastern Austria, and southwestern Hungary. So far, it has attracted very little attention in the seismological communities of those countries. It is missing or has wrong source parameters in all of the relevant earthquake catalogs (including the Seismic Hazard Harmonization in Europe (SHARE) catalog, Stucchi et al., 2013), which may influence seismic hazard assessment in this part of Europe, most critically in the Međimurje region itself. We present contemporary historical data shedding some light on the effects that the earthquake had on settlements mostly in Međimurje, but also elsewhere in Croatia, Slovenia, and Hungary. We were able to assign intensities to 12 localities surrounding the epicenter and to resolve the confusion about its date of occurrence. The intensity points were inverted for the location of the macroseismic hypocenter and epicentral intensity (I0=7.9 MSK [Medvedev–Sponheuer–Karnik]). The epicenter is found to lie on the hanging wall of the reverse Čakovec fault, about 6 km from its surface trace, and 8 km north-northwest of the town of Čakovec. The rather small felt area for an earthquake of this maximum intensity implies a shallow macroseismic focal depth of 6 km. These values of intensity and depth correspond to a macroseismic magnitude of MLm 5.1.

The 1906 Dobrá Voda Earthquake (M=5.7) at the Vienna Basin Transfer Fault: evaluation of the ESI2007 intensity and analysis of the aftershock sequence

Abstract Aftershock identification plays an important role in the assessment and characterization of large earthquakes. Especially, the length of the aftershock sequence is an important aspect of declustering earthquake catalogues and therefore impacts the frequency of earthquakes in a certain region, which is important for future seismic hazard assessment. However, in intraplate regions with low deformation rates and low to moderate seismicity, it is still questionable if aftershocks after a major event may continue for much longer time. In this study, we use one of the earliest instrumentally recorded earthquakes, the 1906 Dobrá Voda earthquake (Ms/Imax=5.7/VIII-IX), to compare different approaches of aftershock determination and their suitability for understanding the recorded earthquake sequence. The Dobrá Voda segment of the Vienna Basin Transfer Fault System is one of the seismically most active zones in Slovakia with the 1906 earthquake as the strongest recorded earthquake. We first assess the epicentral intensity of the earthquake according to the Environmental Intensity Scale (ESI2007) using contemporary descriptions of earthquake effects. This additional information leads to constrain the maximal intensity to IESI2007=IX. This result agrees well with first the assessment of Imax in 1907 and indicates the reliability of this intensity data. In the second step, earthquake data are plotted for two spatial windows extending 13 km and 26 km from the epicenter of the mainshock, respectively. Despite uncertainties regarding the completeness of data due to war times and lack of nearby seismic stations, the overall temporal evolution of seismicity can apparently not be described as an Omori-type aftershock sequence following the event in 1906. Instead, earthquake occurrence within 13 km of the mainshock shows elevated earthquake activity right after the 1906 event that only decays to a lower level of activity within decades after the mainshock. The decline of seismicity therefore occurs over time scales which are much longer than those predicted by the Omori relation. We conclude that today’s seismic activity may still be affected by the 1906 earthquake.

Strong Ulakhan-Chistay earthquake (Ms=5.7) January 20, 2013 in the zone of influence Ulakhan fault system in North East Russia

The results of the interpretation of seismological, geologic–structural, seismotectonic and macroseismic data obtained for the focal zone of the strong Ulakhan-Chistay earthquake (Ms=5.7), which occurred January 20, 2013 in the Chersky seismotectonic zone , on the Eurasia-North America lithospheric plates boundary, are presented. The shock occurred in the zone of a large Ulakhan fault, which is visible in satellite images and can be seen in the topography between the Indigirka and Kolyma Rivers at a distance of 1,500 km. Statistics of seismic observations in the last century and at the beginning of this century show that in the zone of influence of the Ulakhan fault within the crust (~ 35 km thick) at a depth of 7-30 km, more than 14 thousand local events were noted. The epicentral intensity of more than ten of them reached 6–8 on the Russian scale (MSK-64). In addition to high seismicity, additional geodynamic indicators of the reactivation of the Ulakhan fault in modern time were identified, in particular, high heat flux, icing processes, paleo-and modern seismic dislocations, etc.The macro effects of this event on an area of 300 thousand square kilometers were studied in three Arctic regions of Yakutia and in the south of the Magadan region and its epicenter is located by the proximity to the well-preserved paleoseismodislocation Uryun – Takh – Takh, which arose more than a thousand years ago and is clearly visible in the search sistem of Google. As a result, a structural-dynamic model of the Ulakhan fault zone is proposed, explaining the occurrence of the Ulakhan – Chistay earthquake on the basis of the kinematic scheme of the Omulevsky block, which is undergoing extrusion by a collision between the Eurasian and North American lithospheric plates in Northeast Asia.

Intensity estimation for the 2001 Bhuj earthquake, India on ESI-07 scale and comparison with historical 16th June 1819 Allah Bund earthquake: A test of ESI-07 application for intraplate earthquakes

On 26th January 2001, an earthquake of magnitude Mw 7.7 occurred near Bhuj, in northwestern India, resulting in severe environmental effects. No unequivocal primary surface rupture was observed for the earthquake, but it caused widespread liquefaction and lateral spreading in the Rann of Kachchh and Little Rann. After the earthquake, several researchers collected field evidence of secondary surface rupture, rockfall, dry craters, and surface manifestations of liquefaction, including the formation of mud volcanoes and lateral spreads, in the meizoseismal area. Analysis of pre- and post-earthquake satellite images suggests that several “dry” streams in the Rann of Kachchh began to flow due to extensive liquefaction induced by the earthquake. In this present study, the macroseismic intensity of the Bhuj earthquake is evaluated by considering these environmental effects and applying the ESI-07 intensity scale to the affected area. As an outcome, the epicentral intensity of the 2001 Bhuj earthquake was determined to be XI. According to historical records and seismic catalogs, 16th June 1819 Allah Bund earthquake caused prominent surface rupture which was not so clear in the case of 2001 Bhuj earthquake, but the secondary effects were similar for both earthquakes. Considering the environmental effects caused by the 1819 Allah Bund earthquake, an intensity of XI was estimated for the epicentral area. For both earthquakes, the ESI scale yields a significant difference of one to two degrees with the traditional intensity scales. The 2001 Bhuj earthquake and 1819 Allah Bund earthquake shows similar ESI-07 intensity of XI despite of different epicentral locations. This implies the reliability of ESI-07 scale application for different earthquakes of similar dimensions in the same geological setting. This study contributes to the application of ESI-07 scale for Indian earthquakes, especially reverse faulting events, and to the future improvement of the ESI scale with emphasis on its applicability to historical earthquakes on the Indian subcontinent. Also, this study may help in future land use planning in the meizoseismal area of 1919 Allah Bund and 2001 Bhuj earthquakes.

New insights from analysis of historical texts on the 1568 Northeast Xi'an earthquake, Shaanxi, China

A destructive earthquake occurred in Northeast Xi'an, Shaanxi province, on May 25th, 1568 AD, causing many casualties, severe damage to property, and significant disruption to livelihoods. This earthquake has been chosen as a plausible basis for calculating a seismic scenario for the modern city of Weinan, and its surrounding urban areas. Previous studies agreed in assigning a magnitude 6 ¾ to the earthquake but yielded differing epicentral locations and isoseismal intensity maps. We combine textual research on historical earthquake reports with field investigations to reduce the uncertainties, and to place constraints on the ground shaking that would be experienced if such an earthquake were to recur. We show that the counties of Jingyang, Gaoling, and Xianning were the worst hit by the earthquake, with the townships of Yongle, Huijun, Pisha, and Fengzheng (present-day Gaozhuang and Zhangbu township), likely being in the mesoseismal area of this earthquake. Reinterpretation of the historical texts, combined with field observations, indicates that the epicenter of the earthquake was at about 34°28′N and 108°59′E, with an epicentral intensity of Ⅸ+ and an estimated magnitude of 7. The isoseismal contours have major axes-oriented WNW-ESE, in contrast to the more NS alignment inferred from the earlier study of the historical documents. The isoseismal of intensity VIII+encloses, and has its major axis parallel to, the active Weinan-Jingyang fault, which we infer to be the fault that slipped in the May 25th, 1568 earthquake.

УЛАХАН-ЧИСТАЙСКОЕ ЗЕМЛЕТРЯСЕНИЕ 20 января 2013 г. с КР=14.4, Mw=5.6, I0р=8 (Северо-восток Якутии)

The results of interpretation of seismological, geological–geophysical, seismotectonic, and macroseismic da-ta obtained for the focal zone of the strong Ulakhan-Chistay earthquake (Mw=5.6) that occurred on January 20, 2013, in the Chersky Ranges system, at the boundary of lithospheric plates of Eurasia and North Ameri-ca, are presented. The epicenter of the event is confined to Ulakhan-Chistay Ridge, close the Cenozoic-aged Bugchan basin. Comparison is made between the hypocentre parameters of this event determined on the basis of data from regional seismic stations and the solutions based on the data from other seismic agencies worldwide. The earthquake occurred in the zone of the major Ulakhan fault which is seen in space images and is traced in topography between the Indigirka and Kolyma Rivers over a distance of 1500 km. A characteristic feature of the fault is origination within its limits of quakes without aftershocks which was the case during the 2013 event too. Statistics of seismic manifestations observed in the past century and early this century show that over 14 thousand local event were noted in the zone influenced by the Ulakhan fault within the Earth’s crust (~35 km thick) at a depth of 7–30 km. The epicentral intensity of more than ten events reached 6–7 in the Russian scale (MSK-64). Apart from high seismicity, some additional geodynam-ic, indicators of Ulakhan fault reactivation were recognized, particularly a high heat flux, icings, paleo and modern seismodislocations, etc. Macroeffects of the Ulakhan–Chistay earthquake observed over an area of 300 thousand sq. km in three arctic districts of Yakutia and in the south of the Magadan region were studied. The epicentral intensity of this event is 8. This is supperted by close proximity of the regional epicenter to the well–preserved Tirekhtyakh paleoseismodislocation that originaled more than a thousand years ago after the strongest paleo earthquake and is clearly seen the Google search system. It is shown that the epicentral inten-sity of the earthquake corresponds to the regional macroseismic field equation. The comparison of focal mechanism parameters of the 2013 earthquake and morphokinematic characteristic of the Ulakhan fault, to which epicenter is confined, permitted us to confidently determine the crush plane has NW strike and is in-clined to SW at 74–76°. According to seismological data, motions in the earthquake source coincide with the modern type of tectonic motions on the Ulakhan fault and correspond left lateral strike slip. It is supposed that the Ulakhan possesses a higher seismic potential and can generate earthquakes MS ≥6.

Macroseismic Intensity Estimation from Instrumental Ground Motion Recordings in the Case of Small and Moderate Vrancea Subcrustal Earthquakes

Romania is one of the most seismic-prone countries in Europe due to the periodically occurrence of strong intermediate-depth earthquakes in Vrancea seismogenic zone. The Vrancea area is located beneath the South-Eastern Carpathian Arc bend, at the contact between the East - European plate and the Intra-Alpine and Moesian sub-plates. An intense seismic activity is recorded in the mantle, within a narrow, almost vertical descending volume between 60 and 180 km depth. Earthquakes with magnitudes larger than 5.0 (Mw) and macroseismic effects exceeding V MSK degrees on extended populated area occur in Vrancea seismic zone, with a return period of around 2 years. Besides the extended scientific studies, the near real time estimation of the macroseismic intensity recently became mandatory for the insurance companies to cover some of the losses and damages that earthquakes might cause to houses, belongings, and other buildings. The first approach to obtain intensity values was to develop an online environment for collecting people feedback regarding the effects of earthquakes and for the automatic approximation of the intensity. The automatic intensity estimation code from the online feedback proposed by [1], [2] and adopted by [3] for the Romanian earthquakes was improved and used for this study. Additionally, there were used prediction equations to obtain intensity values from the epicentral intensity, and epicentral and hypocentral distances. Besides the estimation of macroseismic intensities from online people feedback and from attenuation relations, equations for conversion of peak ground acceleration in macroseismic intensity were also required for a rapid evaluation of ground motion effects. In order to avoid the increase of the prediction uncertainties, the data must be selected in such a way that they represent the parameters’ rank for which the prediction will be accomplished and the selected data must be representative for the investigated regions and seismic source. In this paper were developed conversion methods from PGA to macroseismic intensity for moderate intermediate depths earthquakes with 4.5<Mw<6.0. All the studies were realised in the case of Vrancea recent (2014-2019) moderate intermediate depth earthquakes, felt on the extra-Carpathian region.

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.

Intensity Attenuation Model Evaluation for Bangladesh with Respect to the Surrounding Potential Seismotectonic Regimes

An effort has been made through this study to evaluate the existing intensity attenuation model (IPE) for the potential seismotectonic regimes in and around Bangladesh. To reach the goal, the seismicity of the concerned tectonic regimes has been analyzed. Apart from evaluating the appropriate intensity model, this research has also assessed the predictive performance of epicentral intensity estimation. Different magnitude types have been made uniform by converting into moment magnitude and subsequently into the Modified Mercalli Intensity scale (MMI). The epicentral intensity conversion following Li in Chinese Earthquakes (Seismological Press, Beijing, 1980) fits best for the study area among the utilized four predictive equations. The epicentral intensity conversion from the moment magnitude shows that small to moderate earthquakes get significantly overestimated. Suitable attenuation models have been applied to the different tectonic regimes based on the criteria of using the IPEs. Among all the utilized IPEs, the relation of Bakun et al. (Bull Seismol Soc Am 93:190–202, 2003) exhibits the highest standard deviation (σ = 1.61) in attenuation with distance. Although the Szeliga et al.’s (Bull Seismol Soc Am 100(2):570–584, 2010) attenuation relation has a standard deviation of 1.22, the intensity decay is little even for the greater distance (~ 800–900 km). Up to Mw 7.0, the IPE of Bindi et al. (Geophys J Int 187(1):327–337, 2011) shows realistic attenuation scenario (with σ = 1.3); however, at lower magnitude range (< Mw 7.0), the intensity starts to decay sharply. Still, the IPE of Bindi et al. (2011) is more realistic in comparison of the shakemaps of the past and in terms of convincible intensity decay with greater distance (~ 500–900 km). However, the intensity close to the epicenter gets very high MMI (XI or larger) value for the major events (Mw ≥ 8.5). Although the IPE of Chandler and Lam (J Asian Earth Sci 20(7):775–790, 2002) has distance constraints, its performance is acceptable considering the attenuation scenario with distance along with the lowest standard deviation (~ 0.92). Considering the seismic events from the only strike-slip Churachandpur Mao fault of the study area, Bakun and Wentworth (Bull Seismol Soc Am 87(6):1502–1521, 1997) relation has been applied to determine the attenuation pattern.

Applicability of Regional Evaluation for Rapid Assessment Models of Earthquake Disaster Life Loss — A case study of Gansu Province

In this paper, typical earthquake disaster life loss assessment models are applied to verify and calculate the historical earthquake cases in the Gansu Province since 1966. The assessment accuracy and applicability of various models in the Gansu Province are studied by means of actual earthquake cases. Results show that: (1) For Ms<5.5 and 5.5≤Ms≤6.0, a life loss assessment model is based on population density, another model based on epicentral intensity proposed, and the national earthquake disaster emergency assessment model are relatively accurate and basically included in the reasonable range; for Ms>6.0, characteristics of the assessed regions, such as physical geography and social economy, should be analyzed to correct the model calculation results and to receive comprehensive assessment results, so as to support emergency decisions. (2) Earthquake disaster life loss assessment models are regionalized and the assessment results are obviously regional. Assessment results of the earthquakes occurred in Hedong Region are not accurate for Hexi Region of Gansu Province.