An integrated assessment of seismic hazard exposure and its societal impact in Seven Sister States of North Eastern Region of India for sustainable disaster mitigation planning

The Seven Sister States of the North Eastern Region of India, located on the complex seismotectonic belt, is characterized by high seismicity. A comprehensive seismic hazard exposure assessment is carried out by quantifying hazard using a probabilistic approach, vulnerability by factor analysis, and exposure mapping by integrating seismic hazard and vulnerability. Peak ground acceleration (PGA) values at bedrock are calculated with the help of ground motion prediction equations (GMPE) for 10% probability of exceedance in 50 years (475 years) and 100 years (950 years), and 2% probability of exceedance in 50 years (2475 years). The resulting spatial distribution of the PGA values considering return periods of 475, 950, and 2475 years are presented through seismic hazard maps. The social vulnerability analysis indicates that 21 districts covering 91.43% area of the state of Assam and the entire state of Tripura are under high vulnerability. With the help of spatial cluster analysis, it is found that 17.14% of the study area are having an average social vulnerability index (SVI) score of 0.329 and therefore can be considered as hotspots. Through seismic hazard analysis, it is observed that more than 50% of the area of North East India is under moderate to very high exposure class. The seismic hazard maps developed can help in disaster mitigation planning and execution leading to sustainable development goals and targets.

About GSZ maps in acceleration units

Задание сейсмических воздействий в отечественных строительных нормах практически не меняется в течение последних 60 лет. Накопленные эмпирические данные по сильным движениям позволяют коренным образом усовершенствовать методику расчета зданий и сооружений на сейсмостойкость. Ожидается снижение погрешностей расчета примерно вдвое. Цель работы. В последнее время много внимания уделяется проблемам построения карт сейсмической опасности в ускорениях. Однако по традиции в нашей стране такие карты оценивают сейсмическую опасность в баллах шкалы сейсмической интенсивности. В большинстве стран сейсмическая опасность оценивается именно в ускорениях. Строились такие карты и в нашей стране. В частности, карты ОСР-97 и ОСР-2012 имели вариант и в ускорениях. Построение карт сейсмической опасности в ускорениях не имеет принципиальных трудностей. Проблема в том, что ускорения не являются адекватной мерой сейсмических воздействий. Более половины века тому назад американские ученые на эмпирическом материале показали, что связь ускорений с баллами, а, следовательно, и с повреждаемостью зданий неоднозначна: шкалы сейсмической интенсивности различны для разных расстояний и грунтов. Ошибка в оценке последствий землетрясения по ускорениям грунта может достигать 2 баллов. Следовательно, расчет ожидаемых воздействий следует производить с учетом других характеристик сейсмических волн. К тому же, попытки построения карт сейсмической опасности строились без учета данных инженерной сейсмологии и с нарушениями правил теории вероятностей и поэтому обладают не только определенными достоинствами, но и серьезными недостатками. Некоторые исследователи считают, что скорости колебаний лучше коррелируются с повреждениями сооружений, по крайней мере, многоэтажных зданий и подземных трубопроводов. Методы работы. Однако анализ эмпирических данных показал, что использование ускорений, скоростей и смещений характеризуется примерно одинаковой точностью. Рассмотрены способы построения карт общего сейсмического районирования. В действующей шкале сейсмической интенсивности ГОСТ Р 57546.2017 приведены оценки корреляции повреждаемости зданий с различными параметрами сейсмических колебаний: ускорениями, скоростями, смещениями, мощностью колебаний грунта. Оценено влияние продолжительности колебаний. Результаты работы. Показано, что дальнейшее повышение надежности расчетов объектов на сейсмостойкость связана с представлением сейсмических воздействий не с амплитудами колебаний, а с энергетическими характеристиками сейсмических волн The specification of seismic effects in domestic building codes has remained practically unchanged over the past 60 years. The accumulated empirical data on strong ground notions make it possible to radically improve the methodology for calculating buildings and other structures for seismic resistance. It is expected that the calculation errors will be reduced by about half. Aim. Recently, much attention has been paid to the problems of developing seismic hazard maps in accelerations. However, by tradition in our country, such maps assess the seismic hazard in terms of the seismic intensity scale. In most countries, seismic hazard is assessed in terms of accelerations. Such maps were also built in our country. In particular, OSR-97 maps also had a variant in acceleration. The construction of seismic hazard maps in accelerations has no fundamental difficulties. The problem is that accelerations are not an adequate measure of seismic effects. More than half a century ago, American scientists, using empirical material, showed that the relationship between accelerations and points, and, consequently, with the damage to buildings, is ambiguous: the seismic intensity scales are different for different distances and grounds. The error in assessing the consequences of an earthquake in terms of ground acceleration can reach 2 points. Therefore, the calculation of the expected impacts should be based on other characteristics of the seismic waves. In addition, attempts to construct seismic hazard maps were built without taking into account the data of engineering seismology and with violations of the rules of probability theory and therefore have not only certain advantages, but also serious drawbacks. Some researchers believe that vibration velocities correlate better with structural damage, at least in multi-storey buildings and underground pipelines. However, the analysis of empirical data showed that the use of accelerations, velocities and displacements is characterized by approximately the same accuracy. Methods. Methods for constructing maps of general seismic zoning, which have a higher accuracy in comparison with existing maps, are considered. In the current scale of seismic intensity GOST R 57546.2017 estimates of the correlation of damage to buildings with various parameters of seismic vibrations are given: accelerations, velocities, displacements, power of ground vibrations. The influence of the duration of the oscillations is estimated. Results. It is shown that a further increase in the reliability of calculations of objects for seismic resistance is associated with the representation of seismic effects not with vibration amplitudes, but with the energy characteristics of seismic waves

Probabilistic seismic hazard maps for California do not perform better relative to historical shaking data when site-specific VS30 is considered

<div> <p>Probabilistic seismic hazard assessments forecast levels of earthquake shaking that should be exceeded with only a certain probability over a given period of time are important for earthquake hazard mitigation. These rely on assumptions about when and where earthquakes will occur, their size, and the resulting shaking as a function of distance as described by ground-motion models (GMMs) that cover broad geologic regions. Seismic hazard maps are used to develop building codes.</p> </div><div> <p>To explore the robustness of maps’ shaking forecasts, we consider how maps hindcast past shaking. We have compiled the California Historical Intensity Mapping Project (CHIMP) dataset of the maximum observed seismic intensity of shaking from the largest Californian earthquakes over the past 162 years. Previous comparisons between the maps for a constant V<sub>S30</sub> (shear-wave velcoity in the top 30 m of soil) of 760 m/s and CHIMP based on several metrics suggested that current maps overpredict shaking.</p> <p>The differences between the V<sub>S30</sub> at the CHIMP sites and the reference value of 760 m/s could amplify or deamplify the ground motions relative to the mapped values. We evaluate whether the V<sub>S30 </sub>at the CHIMP sites could cause a possible bias in the models. By comparison with the intensity data in CHIMP, we find that using site-specific V<sub>S30</sub> does not improve map performance, because the site corrections cause only minor differences from the original 2018 USGS hazard maps at the short periods (high frequencies) relevant to peak ground acceleration and hence MMI. The minimal differences reflect the fact that the nonlinear deamplification due to increased soil damping largely offsets the linear amplification due to low V<sub>S30</sub>. The net effects will be larger for longer periods relevant to tall buildings, where net amplification occurs. </p> <div> <p>Possible reasons for this discrepancy include limitations of the dataset, a bias in the hazard models, an over-estimation of the aleatory variability of the ground motion or that seismicity throughout the historical period has been lower than the long-term average, perhaps by chance due to the variability of earthquake recurrence. Resolving this discrepancy, which is also observed in Italy and Japan, could improve the performance of seismic hazard maps and thus earthquake safety for California and, by extension, worldwide. We also explore whether new nonergodic GMMs, with reduced aleatory variability, perform better than presently used ergodic GMMs compared to historical data.</p> </div> </div>

Seismic hazard and risks for social and infrastructure exposures adjacent to the Baikal–Amur Mainline

<p>Seismic hazard assessment requires an adequate understanding the earthquake distribution in magnitude, space, and time ranges. Laking data for a period of several thousand years makes probabilistic approach to estimating the recurrence time of hazardous ground shaking unreliable and misleading. In spite of theoretical flaws and actual failures on practice, the probabilistic seismic hazard assessment (PSHA) maps keep being actively used both at global and national scales. In recent decades, alternative methodologies have been developed to improve the reliability and accuracy of reproducible seismic hazard maps that pass intensive testing by historical evidence and realistic modelling of scenario earthquakes. In particular, the neo-deterministic seismic hazard assessment (NDSHA) confirms providing reliable and effective input for mitigating object-oriented earthquake risks. The unified scaling law for earthquakes (USLE) is a basic part of NDSHA that generalizes application of the Gutenberg-Richter law (G-RL). The USLE states that the logarithm of expected annual number of earthquakes of magnitude M in an area of linear size L within the magnitude range [M– , M+] follows the relationship log N(M, L) = A + B×(5 − M) + C×log L, where A, B, and C are constants.  Naturally, A and B are analogous to the classical a- and b-values, while C compliments to G-RL with the estimate of local fractal dimension of earthquake epicentres allowing for realistic rescaling seismic hazard to the size of exposure at risk. USLE implies that the maximum magnitude MX expected with p% chance in T years can be obtained from N(MX, L) = p%, then used for estimating and mapping ground shaking parameters by means of the NDSHA algorithms. So far, the reliable USLE based seismic hazard maps tested by historical evidence have been plotted for a number of regions worldwide. We present the USLE based maps of MX computed at earthquake-prone cells of a regular grid, as well as the adapted NDSHA estimates of seismic hazard and risks for social and infrastructure exposures in the regions adjacent to the Russian Federation Baikal–Amur Mainline. The study supported by the Russian Science Foundation Grant No. 20-17-00180.</p>

When color theory meets seismology: Principled visualization design for seismic hazard maps

<p>Probabilistic seismic hazard estimates are a key ingredient of earthquake risk mitigation strategies and are usually communicated through seismic hazard maps. Though evidence exists that visual design properties are key for effective communication using such maps, few authors describe their approach in visualizing seismic hazard. Current maps use colors, legends and data classification schemes which are suboptimal, from the visualization perspective. As such, they have the danger of miscommunicating seismic hazard. We present a set of principles regarding color choice, legend design, and classification of the continuous hazard estimate for categorical mapping. These principles are based on (1) communication goals for the seismic hazard phenomenon, (2) empirically-validated recommendations from the visualization literature and (3) other best practices in map design. We discuss the process of redesigning the German seismic hazard map using these principles. A set of prototype maps adhering to these principles are presented. We also describe ongoing efforts to test the redesigned maps, as well as how to use them to further communicate the uncertainty around probabilistic hazard estimates.</p>