Earthquake hazard and risk assessment based on unified scaling law for earthquakes: Altai–Sayan Region

We apply the general concept of seismic risk analysis based on morphostructural analysis of the territory, pattern recognition of earthquake-prone nodes, and the Unified Scaling Law for Earthquakes, USLE, in another seismic region of Russia to the west from Lake Baikal, i.e., Altai–Sayan Region. The USLE generalizes the empirical Gutenberg–Richter relationship making use of apparently fractal distribution of earthquake sources of different size: \( \log_{10} N\left( {M,L} \right)\, = \,A\, + \,B \cdot \left( {5\, - \,M} \right)\, + \,C \cdot \log_{10} L, \) where N (M, L) is the expected annual number of earthquakes of a certain magnitude M within an seismically prone area of linear dimension L. The local estimates of A, B, and C allow determination of the expected maximum credible magnitude in a given time interval and the associated spread around ground shaking parameters (e.g., peak ground acceleration, PGA, or macroseismic intensity, I₀). Compilation of the corresponding seismic hazard map of Altai–Sayan Region and its rigorous testing against the available seismic evidences in the past is used to model regional maps of specific earthquake risks for population, cities, and infrastructures.     

Tectonic model of seismicity for the northeastern segment of the Amur Plate in the Earth’s two-phased rotation

The spatial distribution of the epicenters and hypocenters is analyzed for earthquakes of 2 ≤ M < 6 that occurred in the northeastern segment of the Amur Plate in two phases of changes in the angular speed of the Earth’s rotation. Groups of seismic events in the magnitude interval of 5 ≤ M < 6 are distinguished in the form of NE-trending seismic clusters regularly alternating along the plane of latitude. The seismic clusters are up to 1500 km long and 180–240 km wide and cover the seismic zones with different geodynamic and seismotectonic conditions of seismicity origination. In terms of the epicentral distributions for earthquakes with 2 ≤ M < 4, seismic activity zones are distinguished; these zones are seen as seimolineaments coupling the Tan Lu seismic zones and the eastern flanks of the latitudinal seismic zones. A scheme of distinguishing the compression and extension zones from the spatial clusters of earthquakes with 5 ≤ M < 6 in two phases of changes in the angular speed of the Earth’s rotation is proposed. This scheme satisfactorily agrees with the model of seismotectonic reconstructions of the compression–extension fields and axes.     

Site response of the Ganges basin inferred from re-evaluated macroseismic observations from the 1897 Shillong, 1905 Kangra,and 1934 Nepal earthquakes

We analyze previously published geodetic data and intensity values for the M _s = 8.1 Shillong (1897), M _s = 7.8 Kangra (1905), and M _s = 8.2 Nepal/Bihar (1934) earthquakes to investigate the rupture zones of these earthquakes as well as the amplification of ground motions throughout the Punjab, Ganges and Brahmaputra valleys. For each earthquake we subtract the observed MSK intensities from a synthetic intensity derived from an inferred planar rupture model of the earthquake, combined with an attenuation function derived from instrumentally recorded earthquakes. The resulting residuals are contoured to identify regions of anomalous intensity caused primarily by local site effects. Observations indicative of liquefaction are treated separately from other indications of shaking severity lest they inflate inferred residual shaking estimates. Despite this precaution we find that intensites are 1–3 units higher near the major rivers, as well as at the edges of the Ganges basin. We find evidence for a post-critical Moho reflection from the 1897 and 1905 earthquakes that raises intensities 1–2 units at distances of the order of 150 km from the rupture zone, and we find that the 1905 earthquake triggered a substantial subsequent earthquake at Dehra Dun, at a distance of approximately 150 km. Four or more M = 8 earthquakes are apparently overdue in the region based on seismic moment summation in the past 500 years. Results from the current study permit anticipated intensities in these future earthquakes to be refined to incorporate site effects derived from dense macroseismic data.     

The Problems of Seismic Risk Prediction for the Territory of the Lower Amur Region: Paleoseismogeological and Seismological Analysis

The studied region is located at the junction between the Pacific and Central Asian seismoactive belts. Macroseismic data on earthquakes of this region are available for the last 150 years, while instrumental seismological observations began in the mid-20th century; however, the recurrence interval of strong earthquakes can be up to several centuries and even thousands of years. In this respect, many areas of the Amur region had been believed to be nearly aseismic until earthquakes occurred there. Paleoseismogeological studies of recent years have allowed the character of Holocene displacements to be estimated for some of the main regional structures. As a result, the main tendencies of the Late Quaternary geological evolution of the region remain uncertain and the potential seismogenerating structures are not completely known. Therefore the problem of revealing new zones and periods of seismic activity is topical for the entire Amur region. The importance of this problem is related to the weak degree of study of the region by contemporary methods of active tectonics, the intensive development of engineering infrastructure, which is vulnerable to seismic impacts, and the necessity of long-term seismic forecasting. The present work provides the results of paleoseismogeological studies of the active faults in the Amur region. On the basis of new data on the magnitude potential of seismogenerating structures based on the magnitudes of historical earthquakes and instrumentally recorded ones, we have estimated the seismic effects from strong deep-focus earthquakes and the attenuation coefficients and calculated radii of the first three isoseismals for crustal earthquakes. By using the methods of statistical modeling, we distinguish the periods when seismic effects increased from earthquakes with 2 ≤ M ≤ 6. It is shown that seismic hazard assessment should take into account the dynamics of the seismic regime, caused by the change of the earthquake source depth. It is found that the epicenters of earthquakes with 5 ≤ M ≤ 6 form non-crossing seismic zones in different phases of changes in the Earth’s annual rotation.     

Acoustic and electromagnetic emissions preceding the earthquake in Kamchatka

In 2013, simultaneous observations of acoustic and electromagnetic emissions ranging from 200 Hz to 11 kHz were carried out in Kamchatka; as a result, abnormal surges of the emissions were registered 1–2 days before seismic events with magnitudes M _LH ≥ 5 at a hypocentral distance up to 200 km. The most likely cause of the occurrence of the abnormal emissions in inherently different fields was activation of deformation processes preceding the earthquakes.     

Tectonic setting and geological manifestations of the 2003 Altai earthquake

Geological and geomorphic manifestations of the source of the earthquake that occurred in the southern Gorny Altai on September 27, 2003, are described. This earthquake, the strongest over the entire history of seismological observations, caused damage to buildings and structures in the Chuya and Kurai basins and was accompanied by exposure of its source at the surface with formation of a system of seismic ruptures trending in the northwestern direction. The linear zone of seismic rupture was traced for more than 70 km on the northern slopes of the North Chuya and South Chuya ranges, and a developed network of related splays was found. The secondary (gravitational and vibrational) seismic dislocations were expressed as downfalls, landslides, and gryphons in the pleistoseist zone. These dislocations occur over an area of approximately 90 × 25 km² that broadly coincides with the region of quakes having intensities of IX–VII. The paleoseismogeological investigations performed in the source region of the 2003 earthquake have shown that seven seismic events with M = 7.0–8.0 occurred in its source over the last 5000 years with a 500-to 900-year recurrence period. The study of the tectonic setting of the earthquake source in the Gorny Altai has allowed northward tracing of the main seismically active zones of the Mongolian and Gobi Altai, where earthquakes with a magnitude M > 7.0 occurred repeatedly, in particular, during the 20th century, and combination of all mountain systems of the Greater Altai into a common high-magnitude seismotectonic province.     

Formalized analysis of crustal seismicity in the Sikhote Alin orogen and adjacent areas

The fractal dimension of the epicentral field of earthquakes (D = 1.6) is determined for the Sikote Alin orogen and adjacent areas. According to this parameter, the region occupies the position between the Kamchatka Peninsula, Kuril Islands (1.61 and 1.69), the East China area, and the Lake Baikal region (1.55 and 1.40). Differentiation of the studied area based on the fractal dimension of the number of earthquakes and on the released energy calculated per unit square shows that the most active crustal areas are associated with the Kharpi–Kur–Priamur’e zone of the northeastern orientation, which is the northern segment of the Tan-Lu transregional fault system. Analysis of the time series of seismic events (MLH ≥ 2.4) in the Sikhote Alin and adjacent areas in the period from 1960 to 2013 shows that the “harmonic” with a 10.5-year period is most clearly displayed. This period (11–13 years) was previously distinguished by B.V. Levin and coauthors from the study of the largest number of earthquakes with M ≥ 4.4 for the period of 1971–2003.     

Precursory seismicity rate changes prior to the large and major earthquakes along the Sagaing fault zone,Central Myanmar

In this study, the seismicity rate changes that can represent an earthquake precursor were investigated along the Sagaing Fault Zone (SFZ), Central Myanmar, using the Z value technique. After statistical improvement of the existing seismicity data (the instrumental earthquake records) by removal of the foreshocks and aftershocks and man-made seismicity changes and standardization of the reported magnitude scales, 3574 earthquake events with a M _w ≥ 4.2 reported during 1977–2015 were found to directly represent the seismotectonic activities of the SFZ. To find the characteristic parameters specifically suitable for the SFZ, seven known events of M _w ≥ 6.0 earthquakes were recognized and used for retrospective tests. As a result, utilizing the conditions of 25 fixed earthquake events considered (N) and a 2-year time window (T _w), a significantly high Z value was found to precede most of the M _w ≥ 6.0 earthquakes. Therefore, to evaluate the prospective areas of upcoming earthquakes, these conditions (N = 25 and T _w = 2) were applied with the most up-to-date seismicity data of 2010–2015. The results illustrate that the vicinity of Myitkyina and Naypyidaw (Z = 4.2–5.1) cities might be subject to strong or major earthquakes in the future.     

Seismicity assessment in and around Syria based on instrumental data: application of Gumbel distributions and Gutenberg-Richter relationship

An instrumental earthquake catalog covering the time span between 1903 and 2007 and for the area bounded by 32°N–38°N and 35°E–43°E has been compiled in this research. The catalog has a magnitude of completeness (M _c ) with 3.5. Least squares and statistical probability Gumbel’s techniques with different approaches have been applied on the instrumental events in order to assess the average recurrence time periods for different earthquake magnitudes. The constants a and b of Gutenberg-Richter and the average recurrence times have been computed firstly for the study area and secondly for the central and northern parts of Dead Sea fault system. The different statistical computations using Knopoff and Kagan formalism are generally in agreement and suggest an average recurrence time of 203 years for an earthquake of magnitude 7 for the region. The occurrence of large well-documented historical earthquakes in Lebanon and western Syria, the existence of active fault segments, the absence of large earthquakes during the study period, the increasing number of the low-magnitude earthquakes, and the continued accumulation of the strain since 1900 indicate therefore the probability of an earthquake occurrence of a large magnitude. This should be permanently taken into consideration in seismic hazard assessment on the local and regional scales.     

Results of a seismic forecasting experiment for the Kamchatka region

The integral results of a seismic forecasting experiment for the powerful M > 7 earthquakes in the Kamchatka region are presented. According to the empirical scheme of the short-term earthquake prediction, since 2002 all officially recorded forecasts, including five deep-focus earthquakes in the Sea of Okhotsk, have been predicted without missing events. The specific character of the features of the earthquake preparation and the annular cloud structures that began to be observed in satellite images near the coast of Japan at the boundary of the Okhotsk plate are analyzed.     

Evaluating of the earthquake hazard parameters with Bayesian method for the different seismic source regions of the North Anatolian Fault Zone

The earthquake hazard parameters and earthquake occurrence probabilities are computed for the different regions of the North Anatolia Fault Zone (NAFZ) using Bayesian method. A homogenous earthquake catalog for M _S magnitude which is equal or larger than 4.0 is used for a time period between 1900 and 2015. Only two historical earthquakes (1766, M _S = 7. 3 and 1897, M _S = 7. 0) are included in Region 2 (Marmara Region) where a large earthquake is expected in the near future since no large earthquake has been observed for the instrumental period. In order to evaluate earthquake hazard parameters for next 5, 10, 20, 50, 100 years, M _max (maximum regional magnitude), β value, λ (seismic activity or density) are computed for the different regions of NAFZ. The computed M _max values are changed between 7.11 and 7.89. While the highest magnitude value is calculated in the Region 9 related to Tokat-Erzincan, the lowest value in the Region 10 including the eastern of Erzincan. The “quantiles” of “apparent” and “true” magnitudes of future time intervals of 5, 10, 20, 50, and 100 years are calculated for confidence limits of probability levels of 50, 70 and 90 % of the 10 different seismic source regions. The region between Tokat and Erzincan has earthquake hazard level according to the determined parameters. In this region the expected maximum earthquake size is 7.8 with 90 % occurrence probability in next 100 years. While the regional M _max value of Marmara Region is computed as 7.61, expected maximum earthquake size is 7.37 with 90 % occurrence probability in next 100 years.     

Recent geodynamics of the Kuril subduction zone

The collected GPS/GLONASS data allow us to reveal new information on the recent geodynamics of the Kuril Island arc. The maximum deformation stress accumulates in the southern and northern parts of the study area, while a long fading transition process of postseismic motions is observed in the central segment of the Kuril arc as a result of the 2006–2007 great Simushir earthquakes of M _w = 8.3 and M _w = 8.1. We have succeeded in revealing the recent interplate coupling geometry of the Pacific and the North American lithospheric plates and also in estimating the seismic potential of different segments of the Kuril subduction zone.     

Probabilistic seismic hazard assessment in the Constantine region,Northeast of Algeria

This paper presents a seismic hazard evaluation and develops an earthquake catalogue for the Constantine region over the period from 1357 to 2014. The study contributes to the improvement of seismic risk management by evaluating the seismic hazards in Northeast Algeria. A regional seismicity analysis was conducted based on reliable earthquake data obtained from various agencies (CRAAG, IGN, USGS and ISC). All magnitudes (M _l, m _b) and intensities (I ₀, I _MM, I _MSK and I _EMS) were converted to M _s magnitudes using the appropriate relationships. Earthquake hazard maps were created for the Constantine region. These maps were estimated in terms of spectral acceleration (SA) at periods of 0.1, 0.2, 0.5, 0.7, 0.9, 1.0, 1.5 and 2.0 s. Five seismogenic zones are proposed. This new method differs from the conventional method because it incorporates earthquake magnitude uncertainty and mixed datasets containing large historical events and recent data. The method can be used to estimate the b value of the Gutenberg-Richter relationship, annual activity rate λ(M) of an event and maximum possible magnitude M _max using incomplete and heterogeneous data files. In addition, an earthquake is considered a Poisson with an annual activity rate λ and with a doubly truncated exponential earthquake magnitude distribution. Map of seismic hazard and an earthquake catalogue, graphs and maps were created using geographic information systems (GIS), the Z-map code version 6 and Crisis software 2012.     

The character of scaling earthquake source spectra for Kamchatka in the 3.5–6.5 magnitude range

The properties of the source spectra of local shallow-focus earthquakes on Kamchatka in the range of magnitudes M _w = 3.5–6.5 are studied using 460 records of S-waves obtained at the PET station. The family of average source spectra is constructed; the spectra are used to study the relationship between M _w and the key quasi-dimensionless source parameters: stress drop Δσ and apparent stress σ_a. It is found that the parameter Δσ is almost stable, while σ_a grows steadily as the magnitude M _w increases, indicating that the similarity is violated. It is known that at sufficiently large M _w the similarity hypothesis is approximately valid: both parameters Δσ and σ_a do not show any noticeable magnitude dependence. It has been established that M _w ≈ 5.7 is the threshold value of the magnitude when the change in regimes described occurs for the conditions on Kamchatka.     

Seismic hazard and probability assessment of Kashmir valley,northwest Himalaya,India

Seismic hazard analysis of the northwest Himalayan belt was carried out by using extreme value theory (EVT). The rate of seismicity (a value) and recurrence intervals with the given earthquake magnitude (b value) was calculated from the observed data using Gutenberg–Richter Law. The statistical evaluation of 12,125 events from 1902 to 2017 shows the increasing trend in their inter-arrival times. The frequency–magnitude relation exhibits a linear downslope trend with negative slope of 0.8277 and positive intercept of 4.6977. The empirical results showed that the annual risk probability of high magnitude earthquake M?≥?7.7 in 50 years is 88% with recurrence period of 47 years, probability of M?≤?7.5 in 50 years is 97% with recurrence period of 27 years, and probability of M?≤?6.5 in 50 years is 100% with recurrence period of 4 years. Kashmir valley, located in the NW Himalaya, encompasses a peculiar tectonic and structural setup. The patterns of the present and historical seismicity records of the valley suggest a long-term strain accumulation along NNW and SSE extensions with the decline in the seismic gap, posing a potential threat of earthquakes in the future. The Kashmir valley is characterized by the typical lithological, tectono-geomorphic, geotechnical, hydrogeological and socioeconomic settings that augment the earthquake vulnerability associated with the seismicity of the region. The cumulative impact of the various influencing parameters therefore exacerbates the seismic hazard risk of the valley to future earthquake events.     

Uncertainties in the estimation of <Emphasis Type="Italic">M</Emphasis><Subscript>max</Subscript>

In the present paper, the parameters affecting the uncertainties on the estimation of M _max have been investigated by exploring different methodologies being used in the analysis of seismicity catalogue and estimation of seismicity parameters. A critical issue to be addressed before any scientific analysis is to assess the quality, consistency, and homogeneity of the data. The empirical relationships between different magnitude scales have been used for conversions for homogenization of seismicity catalogues to be used for further seismic hazard assessment studies. An endeavour has been made to quantify the uncertainties due to magnitude conversions and the seismic hazard parameters are then estimated using different methods to consider the epistemic uncertainty in the process. The study area chosen is around Delhi. The b value and the magnitude of completeness for the four seismogenic sources considered around Delhi varied more than 40% using the three catalogues compiled based on different magnitude conversion relationships. The effect of the uncertainties has been then shown on the estimation of M _max and the probabilities of occurrence of different magnitudes. It has been emphasized to consider the uncertainties and their quantification to carry out seismic hazard assessment and in turn the seismic microzonation.     

Recognition of Strong Earthquake Prone Areas in the Altai–Sayan–Baikal Region

The locations of areas prone to strong earthquakes (M ≥ 6.0) in the Altai–Sayan–Baikal region are determined. Based on a scheme of morphostructural zoning of the region and by using the CORA-3 pattern recognition algorithm, all intersections of morphostructural lineaments are separated into two classes: the highly seismic intersections in the vicinities of which strong earthquakes can occur and low seismic in the vicinities of which only earthquakes with M < 6.0 are possible. Recognition was performed for the vectors the components of which were measured values of the geological–geophysical characteristics describing the respective intersection. The result obtained allows the zones of high seismic hazard to be identified more reliably in the region.

     

Dynamic response characteristics of a rock slope with discontinuous joints under the combined action of earthquakes and rapid water drawdown

In order to study the dynamic response characteristics of a rock slope with discontinuities under the combined action of earthquakes and rapid water drawdown, a large-scale shaking table test was performed on a rock slope with discontinuous joints. Wenchuan earthquake (WE) seismic records were performed to investigate the horizontal and vertical acceleration response and displacement response. In particular, three-dimensional optical measurement techniques was used to obtain the slope surface displacements. A comparison was made on the seismic response according to the analysis of PGD (peak ground displacement) and M _PGA (acceleration amplification coefficient) of the modeled slope. The results show that the experimental slope mainly underwent settlement and horizontal deformation when the WE records were applied in the z and x directions, respectively. The slope was first shaken by the P wave, which caused the differential settlement to occur at the surface slope; then, the slope was shaken more severely by the S wave, which led to a greater horizontal deformation. Moreover, analysis of the ΔPGD (increment of PGD) and ΔM _PGA (increment of M _PGA) under rapid drawdown suggests that the rapid water drawdown mainly impacts the deformation of the surface slope, particularly between the high and low water levels. The water infiltration through the cracks softened the material of the surface slope, and the rapid drawdown also enhanced the slope deformation. In addition, the damage evolution process of the slope can be identified, mainly including three stages: an elastic stage (<?0.168 g), a plastic stage (0.168–0.336 g), and a failure stage (>?0.336 g).     

Properties of the aftershocks sequences of the 2000 and 2002 earthquakes in Aksehir-Afyon graben,west-central Anatolia,Turkey

The b-value of the Gutenberg–Richter’s frequency–magnitude relation and the p-value of the modified Omori law, which describes the decay rate of aftershock activity, were investigated for more than 500 aftershocks in the Aksehir-Afyon graben (AAG) following the 15 December 2000 Sultandagi–Aksehir and the 3 February 2002 Çay–Eber and Çobanlar earthquakes. We used the Kandilli Observatory’s catalog, which contains records of aftershocks with magnitudes ≥2.5. For the Çobanlar earthquake, the estimated b-values for three aftershock sequences are in the range 0.34 ≤  b ≤ 2.85, with the exception of the one that occurred during the first hour (4.77), while the obtained p-values are in the range 0.44 ≤ p ≤ 1.77. The aftershocks of the Sultandagi earthquake have a high p-value, indicating fast decay of the aftershock activity. A regular increase of b can be observed, with b < 1.0 after 0.208 days for the Çay–Eber earthquake. A systematic and similar increase and decrease pattern exists for the b- and p-values of the Çobanlar earthquakes during the first 5 days.     

Climate extremes: an observation and projection of its impacts on food production in ASEAN

Multifractal behaviour of interevent time sequences is investigated for the earthquake events in the NW Himalaya, which is one of the most seismically active zones of India and experienced moderate to large damaging earthquakes in the past. In the present study, the multifractal detrended fluctuation analysis (MF-DFA) is used to understand the multifractal behaviour of the earthquake data. For this purpose, a complete and homogeneous earthquake catalogue of the period 1965–2013 with a magnitude of completeness M _w 4.3 is used. The analysis revealed the presence of multifractal behaviour and sharp changes near the occurrence of three earthquakes of magnitude (M _w ) greater than 6.6 including the October 2005, Muzaffarabad–Kashmir earthquake. The multifractal spectrum and related parameters are explored to understand the time dynamics and clustering of the events.