Historical Earthquake Catalogs Research Articles

A harmonised instrumental earthquake catalogue for Iceland and the northern Mid-Atlantic Ridge

Abstract. A comprehensive catalogue of historical earthquakes, with accurate epicentres and harmonised magnitudes is a crucial resource for seismic hazard mapping. Here we update and combine catalogues from several sources to compile a catalogue of earthquakes in and near Iceland, in the years 1900–2019. In particular the epicentres are based on local information, whereas the magnitudes are based on teleseismic observations, primarily from international online catalogues. The most reliable epicentre information comes from the catalogue of the Icelandic Meteorological Office, but this is complemented with information from several technical reports, scientific publications, and newspaper articles. The catalogue contains 1281 moment magnitude (Mw) ≥4 events, and the estimated completeness magnitude is Mw 5.5 in the first years, going down to Mw 4.5 for recent years. The largest magnitude is Mw 7.0. Such merging of local data and teleseismic catalogues has not been done before for Icelandic earthquakes, and the result is an earthquake map with much more accurate locations than earlier maps. The catalogue also lists 5640 additional earthquakes on the Mid-Atlantic Ridge, north of 43∘, with both epicentres and magnitudes determined teleseismically. When moment magnitudes are not available, proxy Mw values are computed using χ2 regression, normally on the surface-wave magnitude but exceptionally on the body-wave magnitude. Magnitudes of Mw≥4.5 have associated uncertainty estimates. The actual combined seismic moment released in the Icelandic earthquakes is found to be consistent with the moment estimated using a simple plate motion model, indicating that the seismic activity of the catalogue period might be typical of any 120-year time span. The catalogue is named ICEL-NMAR, and it is available online at http://data.mendeley.com (last access: 19 July 2021).

Bayesian Parameter Estimation for Space and Time Interacting Earthquake Rupture Model Using Historical and Physics-Based Simulated Earthquake Catalogs

ABSTRACTThis article introduces a framework to supplement short historical catalogs with synthetic catalogs and determine large earthquakes’ recurrence. For this assessment, we developed a parameter estimation technique for a probabilistic earthquake occurrence model that captures time and space interactions between large mainshocks. The technique is based on a two-step Bayesian update that uses a synthetic catalog from physics-based simulations for initial parameter estimation and then the historical catalog for further calibration, fully characterizing parameter uncertainty. The article also provides a formulation to combine multiple synthetic catalogs according to their likelihood of representing empirical earthquake stress drops and Global Positioning System-inferred interseismic coupling. We applied this technique to analyze large-magnitude earthquakes’ recurrence along 650 km of the subduction fault’s interface located offshore Lima, Peru. We built nine 2000 yr long synthetic catalogs using quasi-dynamic earthquake cycle simulations based on the rate-and-state friction law to supplement the 450 yr long historical catalog. When the synthetic catalogs are combined with the historical catalog without propagating their uncertainty, we found average relative reductions larger than 90% in the recurrence parameters’ uncertainty. When we propagated the physics-based simulations’ uncertainty to the posterior, the reductions in uncertainty decreased to 60%–70%. In two Bayesian assessments, we then show that using synthetic catalogs results in higher parameter uncertainty reductions than using only the historical catalog (69% vs. 60% and 83% vs. 80%), demonstrating that synthetic catalogs can be effectively combined with historical data, especially in tectonic regions with short historical catalogs. Finally, we show the implications of these results for time-dependent seismic hazard.

Seismic hazard maps based on Neo-deterministic Seismic Hazard Assessment for China Seismic Experimental Site and adjacent areas

Many devastating earthquakes inflicted heavy casualties and property losses in the seismically active China Seismic Experimental Site area (CSES: 97.5° ~ 105.5°E, 21° ~ 32°N). We performed a first-order seismic zoning based on Neo-deterministic Seismic Hazard Assessment (NDSHA) in the study area delimited by 94° ~ 108°E and 19° ~ 35°N, containing the South-East margin of the Tibetan Plateau and the Sichuan-Yunnan region. The seismic hazard is expressed by maps of peak ground displacement (PGD), peak ground velocity (PGV) and design ground acceleration (DGA) values, extracted from synthetic seismograms computed at a regional scale and mapped on a regular grid of 0.2° × 0.2° over the study area. For the computation of synthetic seismograms, we considered and updated all the available geophysical-geological-tectonic information, including historical and instrumental earthquake catalogues, seismogenic zones, seismogenic nodes, focal mechanisms, and geophysical structural models. We tested the performance of our assessments with available data (i.e., after the Great Wenchuan (2008, May 12th, Ms = 8.0) and Lushan (2013, April 20th, Ms = 7.0) earthquakes) and verified the negligible influence of large events located “far” from the study area. The results indicate the high seismic hazard of the region, with a particular attention (i.e., where DGA > 0.6 g) to the areas located around the main fault zones, e.g., the Longmenshan, Anninghe and Zemuhe Fault Zones. These first-order NDSHA zoning findings may serve as a knowledge basis to support both large- to mid-range preparedness actions and (multi-scenario) site-specific studies.

Bayesian Estimation of the ETAS Model for Earthquake Occurrences

ABSTRACT The epidemic-type aftershock sequence (ETAS) model is widely used in seismic forecasting. However, most studies of ETAS use point estimates for the model parameters, which ignores the inherent uncertainty that arises from estimating these from historical earthquake catalogs, resulting in misleadingly optimistic forecasts. In contrast, Bayesian statistics allows parameter uncertainty to be explicitly represented and fed into the forecast distribution. Despite its growing popularity in seismology, the application of Bayesian statistics to the ETAS model has been limited by the complex nature of the resulting posterior distribution, which makes it infeasible to apply to catalogs containing more than a few hundred earthquakes. To combat this, we develop a new framework for estimating the ETAS model in a fully Bayesian manner, which can be efficiently scaled up to large catalogs containing thousands of earthquakes. We also provide easy-to-use software that implements our method.

Physics‐Based Earthquake Simulations in Slow‐Moving Faults: A Case Study From the Eastern Betic Shear Zone (SE Iberian Peninsula)

AbstractIn regions with slow‐moving faults, the incompleteness of earthquake and fault data complicates the study of seismic hazard. The instrumental and historical seismic catalogs cover a short period compared with the long‐time interval between major events. Paleoseismic evidence allows us to increase the time frame of actual observations, but data is still scarce and imprecise. Physics‐based earthquake simulations overcome the limitations of actual earthquake catalogs and generate long‐term synthetic seismicity. The RSQSim earthquake simulator used in our study reproduces the earthquake physical processes based on a 3D fault model that contains the kinematics, the long‐term slip rates and the rate‐and‐state friction properties of the main seismogenic sources of a region. The application of earthquake simulations to the Eastern Betic Shear Zone, a slow fault system at southeastern Spain, allows the compilation of 100 kyr‐synthetic catalogs ofMW > 4.0 events. Multisection earthquakes and complete ruptures of some faults in this region, preferentially on strike‐slip dominant ruptures, are possible according to our simulations. The largestMW > 6.5 events are likely as a result of jumping ruptures between the Carboneras and the Palomares faults, with recurrence times of < 20,000 years; and less frequently between the Alhama de Murcia and the Los Tollos faults. A great variability of interevent times is observed between successive synthetic seismic cycles, in addition to the occurrence of complex co‐ruptures between faults. Consequently, the occurrence of larger earthquakes, evenMW ≥ 7.0, cannot be ruled out, contrasting with the low to moderate magnitudes recorded in the instrumental and historical earthquake catalog.

Time frame for future large earthquakes near İstanbul based on east-to-west decelerating failure of the North Anatolian Fault

Large earthquakes that have occurred along the North Anatolian Fault (NAF) were analysed to elaborate the time frame of future large earthquakes near İstanbul. The historical earthquake catalog that was compiled covered 1 nearly complete and 2 fully complete failures of the NAF between 1250 and 2000 AD. These data were used to investigate the space-time systematics of M ≥ 7.0 earthquakes. The catalogue identified an east-to-west decelerating domino-like failure of the NAF. The deceleration starts around the western tip of the 1944 Gerede rupture. This suggested that failure of the remaining unruptured ~250-km section in the west (İstanbul to Saros) will take substantially longer than failure of the already ruptured ~950-km section in the east (Karlıova to İzmit). The calculations indicated that complete failure of the NAF will last for 243 ± 3 years. The deceleration could not be explained by strain partitioning between the subparallel strands of the NAF in the Marmara region.

Strong Earthquakes Recurrence Times of the Southern Thessaly, Greece, Fault System: Insights from a Physics-Based Simulator Application

The recurrence time, Tr, of strong earthquakes above a predefined magnitude threshold on specific faults or fault segments is an important parameter, that could be used as an input in the development of long-term fault-based Earthquake Rupture Forecasts (ERF). The amount of observational recurrence time data per segment is often limited, due to the long duration of the stress rebuilt and the shortage of earthquake catalogs. As a consequence, the application of robust statistical models is difficult to implement with a precise conclusion, concerning Tr and its variability. Physics-based earthquake simulators are a powerful tool to overcome these limitations, and could provide much longer earthquake records than the historical and instrumental earthquake catalogs. A physics-based simulator, which embodies known physical processes, is applied in the Southern Thessaly Fault Zone (Greece), aiming to provide insights about the recurrence behavior of earthquakes with Mw ≥ 6.0 in the six major fault segments in the study area. The build of the input fault model is made by compiling the geometrical and kinematic parameters of the fault network from the available seismotectonic studies. The simulation is implemented through the application of the algorithm multiple times, with a series of different input free parameters, in order to conclude in the simulated catalog which showed the best performance in respect to the observational data. The detailed examination of the 254 Mw ≥ 6.0 earthquakes reported in the simulated catalog reveals that both single and multiple segmented ruptures can be realized in the study area. Results of statistical analysis of the interevent times of the Mw ≥ 6.0 earthquakes per segment evidence quasi-periodic recurrence behavior and better performance of the Brownian Passage Time (BPT) renewal model in comparison to the Poissonian behavior.

Seismic hazard of multi-segment rupturing for the Anninghe–Zemuhe–Daliangshan fault region, southeastern Tibetan Plateau: constraints from geological and geodetic slip rates

The Anninghe–Zemuhe–Daliangshan region is deformed by two parallel faults, i.e., the Anninghe–Zemuhe fault and the Daliangshan fault. A large seismic gap that characterizes the AZD region in the past 30 years has attracted significant research attentions to study the seismic hazard of these faults. However, it still remains a matter of debate whether the southern part of the Anninghe fault was ruptured with the Zemuhe fault in the 1850 M7.5 earthquake. The multi-segment rupture probabilities should be considered in the seismic hazard analysis. In this study, we divide the Anninghe fault, the Zemuhe fault and the Daliangshan fault into segments which are then used to build different multi-segment rupture combination models. First, we invert the fault slip rate in an elastic block model. Using both the geological and inverted geodetic slip rates as input constraints, we model the seismicity rates on the fault segments. Then, we compare the modeled seismicity rates with the historical earthquake catalog to test the validity of the models. The model, which does not consist of the multi-segment span the Anninghe fault and the Zemuhe fault, and the multi-segment combinations among the segments of the south Daliangshan fault and the north Xiaojiang fault, has the seismicity rates generally consistent with the fault slip rates and historical records. Finally, we use the compatible fault model to calculate the 475-year PGA values. Our modeled PGA values, from both the geological and geodetic slip rates, are averagely higher than those from the National Zonation Map. This methodology is more reasonable as it considers the fault slip rate and multi-segment rupture.

Seismic study and spatial observations of a & b – values for the different earthquake hazard zones of India

This paper study the recent seismicity in Earthquake hazard zones in India. A large historical earthquake event catalog to cover the period of 1900-2018, the parameters date, time, latitude, longitude, depth and magnitude has been used to calculating frequency-magnitude distribution (b-value) of seismic hazard zones in India. To convert different magnitude scales into a single moment magnitude scale, the general orthogonal regression relation is used. Gamma distribution used for variable corrections also de-clustering method has used for removal of any non-Poisson distribution. The Indian seismic hazard zones are divided into five major seismic sources zones. The seismicity is characterized by Gutenberg-Richter relation. The parameter ‘b’ of FMD and relationship have been determined for these five seismic zones having different vulnerability environment. The ‘b’ values ranges between 0.43 to 1.16. The difference between the b parameters and seismic hazard level from seismic zones II to V considered for the study of high seismo-tectonic complexity and crustal heterogeneity, the parameter ‘a’ value changes accordingly the seismicity of the regions. The lowest b-values found in seismic zone II. The highest FMD b-value has been found in the seismic zone IV. Such high seismicity b-values may be associated with high heterogeneity. In this high b-value predict the low strength in the crust as well as seismic instabilities of that zone. These observations recommend not suggesting the location of important projects like atomic power stations, hydroelectric power stations, neutrino observatory projects, satellite town projects.

Susceptibility to Seismic Amplification and Earthquake Probability Estimation Using Recurrent Neural Network (RNN) Model in Odisha, India

The eastern region of India, including the coastal state of Odisha, is a moderately seismic-prone area under seismic zones II and III. However, no major studies have been conducted on earthquake probability (EPA) and hazard assessment (EHA) in Odisha. This paper had two main objectives: (1) to assess the susceptibility of seismic wave amplification (SSA) and (2) to estimate EPA in Odisha. In total, 12 indicators were employed to assess the SSA and EPA. Firstly, using the historical earthquake catalog, the peak ground acceleration (PGA) and intensity variation was observed for the Indian subcontinent. We identified high amplitude and frequency locations for estimated PGA and the periodograms were plotted. Secondly, several indicators such as slope, elevation, curvature, and amplification values of rocks were used to generate SSA using predefined weights of layers. Thirdly, 10 indicators were implemented in a developed recurrent neural network (RNN) model to create an earthquake probability map (EPM). According to the results, recent to quaternary unconsolidated sedimentary rocks and alluvial deposits have great potential to amplify earthquake intensity and consequently lead to acute ground motion. High intensity was observed in coastal and central parts of the state. Complicated morphometric structures along with high intensity variation could be other parameters that influence deposits in the Mahanadi River and its delta with high potential. The RNN model was employed to create a probability map (EPM) for the state. Results show that the Mahanadi basin has dominant structural control on earthquakes that could be found in the western parts of the state. Major faults were pointed towards a direction of WNW–ESE, NE–SW, and NNW–SSE, which may lead to isoseismic patterns. Results also show that the western part is highly probable for events while the eastern coastal part is highly susceptible to seismic amplification. The RNN model achieved an accuracy of 0.94, precision (0.94), recall (0.97), F1 score (0.96), critical success index (CSI) (0.92), and a Fowlkes–Mallows index (FM) (0.95).

Catalog of Preinstrumental Earthquakes in Central Mexico: Epicentral and Magnitude Estimations Based on Macroseismic Data

ABSTRACTWe present the first parametric catalog of historical earthquakes in Mexico from 1469 to 1912 composed of 323 historical earthquakes. The historical earthquakes were assigned to specific seismotectonic provinces, and attenuation relations of seismic intensity versus distance were calculated using instrumental earthquakes. The intensity data were inverted using a linear regression for the best-fitting magnitude and source location. From the 323 events identified in the historical record, magnitude and source location were determined for 40 earthquakes from 1568 to 1912. The historical subduction earthquakes are distributed uniformly along the coast. There is, however, a conspicuous absence of subduction earthquakes where the great 1985 Michoacán earthquakes took place. The data also show a large number of earthquakes Mw>7 in the presumed Guerrero gap in the past 320 yr. The source parameters of in-slab earthquakes were obtained for 10 earthquakes that took place in the nineteenth and early twentieth centuries. The analysis of completeness of the historical and instrumental International Seismological Centre-Global Earthquake Model catalogs of subduction earthquakes Mw>7.0 show similar values of the slope of the Gutenberg–Richter relation between 1.62 and 1.95. The large b-values appear to reflect the apparently anomalous large number of earthquakes in the magnitude range Mw 7.4–7.7 and an absence of events Mw∼7. This magnitude distribution suggests that the seismicity in the Mexican subduction zone is dominated by characteristic earthquakes in the magnitude range Mw 7.4–7.7, with larger earthquakes Mw>8 showing longer recurrence times. The catalog of historical subduction earthquakes appears to be complete for Mw>7.5. The catalog of crustal earthquakes in the Trans-Mexican volcanic belt is complete since 1568 for events Mw>6.4. Completeness of the catalog of in-slab earthquakes was not estimated due to the short record for this type of event.

A New Concept of Intensity Data Area and Its Effect on the Parameter Determination of Historical Earthquakes

Abstract In ancient China, the government annals provided abundant historical earthquake records, which lasted more than 2000 yr. In some cases, the earthquake damage descriptions from the high-tier government annals are so concise that the specific place names were omitted, even the names of towns where the damage might have actually occurred. The intensity data point (IDP) was assigned to the capital town of the high-tier government, which might lead to large uncertainties in the historical earthquake parameters. A new concept of intensity data area (IDA) is proposed specifically to deal with this issue. An approach on how to convert the IDA to an IDP, based on nonseismological information, is described. In this process, we emphasize the effectiveness of field trips to investigate local features, such as natural environment, population distribution, historical administration zoning, and so forth. As case examples, two historical earthquakes in the Ming Dynasty are analyzed. The documentations of both earthquakes have a common problem, in that some damage was described with the name of the highest-tier local government (Fu); this led to the dispute about the parameter of historical earthquakes. With the proposed method, the IDA for Fu is successfully converted to an IDP at the suitable site. This is the key step to solve the dispute and reduce the parameter uncertainty. Our results have revealed that the parameters of both case earthquakes in the latest edition of the catalog (“The Catalog of Chinese Historical Strong Earthquakes (2300 B.C.–A.D. 1911)”) were wrong (Min et al., 1995). It is noteworthy that the latest edition of the catalog is currently in common use. To avoid the misuse of the catalog, it is better that the parameters in the catalog be restudied, especially for those labeled with large uncertainties.

Site-Specific Response Spectra: 2nd District of Cagayan de Oro City, Philippines

Building codes are updated advertently to address the catastrophic effect of earthquakes. One way of mitigating it is the development of a site-specific response spectrum. In the Philippines, the National Structural Code of the Philippines (NPSC) is the recognized National Building Code adopting the 1997 Uniform Building Code (UBC). The NSCP uses the 10% probability of exceedance in a 50-year period with a return period of 475 years. In this study, site-specific response spectra were developed in the 2nd District of Cagayan de Oro City using a 300-km radius, with coordinates of 8.235° (latitude) and 124.024° (longitude) as the center point of the study area, using the same probability of exceedance in a 50-year period. Historical earthquake catalogs were gathered from the United States Geological Survey and the Department of Science and Technology – Philippine Institute of Volcanology and Seismology. Local soil condition was assimilated in the study to take into account the soil response. Finally, site-specific response spectra were developed using the probabilistic seismic hazard analysis where substantial results are achieved, i.e., the UBC 1997 design response spectrum is remarkably high in spectral acceleration values at 0.01, 0.20, 1.0, 2.0, 3.0, 4.0 and 5.0 s at 0.44, 1.1, 1.1, 0.7, 0.36, 0.26 and 0.20 g compared to the maximum site-specific response spectra of the study area of the same period at 0.39, 0.92, 0.23, 0.10, 0.07, 0.05 and 0.04 g spectral accelerations, respectively.

Seismic hazard assessment for mainland China based on spatially smoothed seismicity

Probabilistic seismic hazard assessment for mainland China is carried out by using spatially smoothed seismic source models obtained using the historical earthquake catalogue and two kernel smoothing techniques. The first one smooths the cumulative event count and the second one smooths the earthquake occurrence rate. For the analysis, the completeness of the catalogue is assessed and the k-mean seismic analysis results are used to aid the assignment of the regions. It is shown that the estimated parameters for the Gutenberg-Richter relation by using the maximum likelihood–based approach are consistent with those estimated by using the least-squares based approach by considering unequal observation periods. The developed seismic hazard maps indicate that the use of the smoothed source model obtained by smoothing the cumulative event count leads to spatially smeared seismic hazard. The use of the smoothed source model obtained based on smoothing the occurrence rate results in the seismic hazard map to have more spatial details. The seismic hazard assessment results indicate that, on average, the ratio of the 2475-year to 475-year return period values of PGA is about 2 and the ratio of the 2475-year to 50-year return period values of PGA is about 8. These ratios are associated with large scatters. A comparison of the normalized UHS and the Chinese design code recommended standardized design spectrum indicates that the latter is conservative as compared to the former for vibration periods outside of 0.1 to 0.2 s, and that the shape of the latter differs from that of former.

A database of potential paleoseismic evidence in Switzerland

Paleoseismological evidence is indispensable for the identification of large prehistoric earthquakes and the extension of the temporal coverage of historical and instrumental earthquake catalogues. In the geological record, diverse traces of past earthquakes are found. This study presents a database of potential primary and secondary evidence for seismic activity in the past 20,000 years in Switzerland. The database includes data from sedimentological, archaeological, speleological and geomorphological research. This unique dataset allows identifying periods during which the geologic record reveals enhanced occurrence of evidence that are further discussed as potentially earthquake-triggered. For the most recent 700 years, an increased occurrence of evidence features was found. This clustering is an effect of the historical earthquakes. Furthermore, periods with enhanced occurrence are identified at six phases during the past 20,000 years. Even though dating uncertainties for the geological record are large (e.g. 14C calibration range) and an unequivocal attribution of earthquakes as trigger mechanism for secondary evidence is not possible, the database reflects the natural-hazard potential of a region and represents valuable information for seismic hazard assessment. Furthermore, despite the uncertainty regarding the definition of the trigger mechanism, we propose that the database can be used to validate and improve earthquake-hazard models.

An updated parametric catalog of historical earthquakes around the Dead Sea Transform Fault Zone

In this study, we present the work done to review the existing historical earthquake information of the Dead Sea Transform Fault Zone (DSTFZ). Several studies from various sources have been collected and reassessed, with the ultimate goal of creating of new homogenized parametric earthquake catalog for the region. We analyze 244 earthquakes between 31 BC and 1900, which are associated with the geographical buffer extending from 27 N to 36 N and from 31 E to 39 E. Of these, 93 were considered real seismic events with moment magnitude (Mw) greater than 5 that indeed occurred within this zone. While we relied on past parametric data and did not assign new macroseismic intensities, magnitude values, or epicenters for several controversial events, we did however resort to the primary sources to obtain a more critical perspective for the various assigned macroseismic intensities. In order to validate the derived parametric information, we tried to associate the events present in the historical records, with any evidence coming from past field investigations, i.e., geological or archaeological studies. Acknowledging the uneven quality and quantity of data reporting each event, we provided each entry with an uncertainty range estimate. Our catalog lists 33 events of Mw ≥ 6 absent from the latest published compilation with compatible time span and areal coverage. The whole catalog is considered complete down to Mw 7 and in certain areas down to Mw 6 after the year 1000, with majority of the larger earthquakes located in the part of DSTFZ, which extends from the southeast part of Dead Sea lake till Antioch.

Non-Poissonian Earthquake Occurrence Probability through Empirical Survival Functions

Earthquake engineering normally describes earthquake activity as a Poissonian process. This approximation is simple, but not entirely satisfactory. In this paper, a method for evaluating the non-Poissonian occurrence probability of seismic events, through empirical survival probability functions, is proposed. This method takes into account the previous history of the system. It seems robust enough to be applied to scant datasets, such as the Italian historical earthquake catalog, comprising 64 events with M ≥ 6.00 since 1600. The requirements to apply this method are (1) an acceptable knowledge of the event rate, and (2) the timing of the last two events with magnitude above the required threshold. I also show that it is necessary to consider all the events available, which means that de-clustering is not acceptable. Whenever applied, the method yields a time-varying probability of occurrence in the area of interest. Real cases in Italy show that large events obviously tend to occur in periods of higher probability.

Millennial Record of Earthquakes in the Carpathian-Pannonian Region: Historical and Archaeoseismology

This is a short essay on earthquakes in the Carpathian-Pannonian region and its surroundings. Earthquakes have been recorded using seismographs since 1902 in Hungary. The relatively small number of seismic events and the long return period of major earthquakes make it necessary to use historical data in order to assess seismic hazard. Historical earthquake catalogues aim for exhaustiveness both in time and space, but they are limited by the lack of documentary data. A simple arithmetical assessment is provided to estimate our lack of knowledge of past seismic events. All destructive earthquakes of the twentieth century (above magnitude 5) are included in the catalogue (100%). Of the seismic events which took place in the seventeenth, eighteenth, and nineteenth centuries, only 23% are on record, while this figure drops to 4.6 percent for the eleventh–sixteenth centuries and 0.2 percent for the first millennium AD. On average, we have no information about 90% of the destructive earthquakes which occurred in the Carpathian-Pannonian region over the course of the past two millennia. According to both instrumental measurements and historical sources, there were relatively few earthquakes in the central era of the period of time in question. This era coincides roughly with the two centuries of Ottoman rule (the sixteenth and seventeenth centuries). Were there really few earthquakes over the course of these two centuries, or we do not have the relevant records? We contend that warfare resulted in the destruction of settlements and the annihilation of documents. Fragile historical documents can be supplemented by the study of robust edifices, an approach to the study of the past which is known as archaeoseismology. Evidence of damage and destruction can be identified, and earthquake parameters can be assessed. One can find evidence corroborating other sources indicating an earthquake (e.g. Savaria), and one can also identify traces of previously unknown seismic events (Visegrád). One can also assign intensity values to the existing historical records. Damage observed to a Roman road in Savaria, to the medieval donjon of Nagyvázsony offers support for our fundamental contention. In order to understand the seismic hazard that was faced in the Carpathian-Pannonian region, renewed study of historical sources and new archaeoseismological investigations are needed.

Did earthquakes strike Machu Picchu?

The Historic Sanctuary of Machu Picchu (Cusco, Peru) is one of the most important archaeological monuments in Peru and worldwide. Machu Picchu is classified as a UNESCO World Heritage site and at risk from climatic change. However, the seismic centennial history of Peru reports large earthquakes generated both along the subduction zone (Mw8) and on active crustal faults along the Andean Cordillera (Mw7). It is therefore important to know if Machu Picchu is located in an area of seismic hazard and then to take measures to mitigate potential seismic hazards. Due to the short historical earthquake catalogue (< 500 years) and the absence of significant recent instrumental seismicity in the site’s vicinity (radius of < 30 km), our knowledge about the seismic hazard in Machu Picchu is limited. The earthquakes of 1650 and 1950 affected Cusco city and surrounding areas, but without damage descriptions in Machu Picchu (80 km away) (Silgado Ferro 1978). In this study, we make the first attempt to use the analysis of earthquake archaeological effects (EAEs) and their differentiation from the effects generated by slope movements (creep) to investigate the past occurrence of strong earthquakes at the site. The application of geological structural analysis to the deformations observed in Machu Picchu shows two directions of the mean ground movement: N020° E and N110° E. Two earthquakes that affected Machu Picchu during its construction generated these directions. This kind of data should be used in the future to protect this important archaeological site.

On the Ground‐Motion Models for Chinese Seismic Hazard Mapping

AbstractThe ground‐motion models (GMMs) used to map seismic hazard in China were developed based on the so‐called projection method, assuming relations of a pair of predicted macrointensities and of a pair of predicted ground‐motion measures in two different regions. The use of such a method is necessary because the ground‐motion records of a large number of strong earthquakes are lacking in mainland China, although the catalog of historical Chinese earthquakes is relatively rich. A critical review of the GMMs adopted to develop the third‐, fourth‐, and fifth‐generation Chinese seismic hazard maps (CSHMs) for mainland China suggests that some of the information used to project these models, such as the earthquake magnitude interpretation and GMM for the macrointensity, may need additional justification, and that the standard deviation (sigma) of the GMMs may be low. Also, new GMMs applicable to mainland China are developed based on the projection method and a set of the GMMs from the Next Generation Attenuation relationships. The results obtained using newly projected GMMs and seismic hazard analysis indicate that the ratio of the return period values of the peak ground acceleration obtained using the newly projected GMMs and using the GMMs adopted for the fifth‐generation CSHM is about 1.35 for a return period range from 50 to 2475 yr. Part of this increase is attributed to the differences in the standard deviations of residuals for the newly projected GMMs and the adopted GMMs used to map seismic hazard for mainland China. The results also suggest that the shape of the adopted seismic design spectrum in Chinese structural design code differs from the uniform hazard spectra obtained based on the newly projected GMMs for simple seismic source zones.