Attenuation laws and seismic hazard assessment

In the present study, the seismic hazard in the city of Patras, central Greece, is estimated. The computations are based on a slightly modified version of the method proposed by Cornell, allowing the introduction of individual attenuation laws for each seismic source.The obtained results emphasize the dependence of hazard on attenuation and the importance of the use of local attenuation laws in seismic hazard assessment.Paper presented at the 21st General Assembly of the European Seismological Commission, held in Sofia, 1988.     

Attenuation laws and seismic hazard assessment

In the present study, the seismic hazard in the city of Patras, central Greece, is estimated. The computations are based on a slightly modified version of the method proposed by Cornell, allowing the introduction of individual attenuation laws for each seismic source. The obtained results emphasize the dependence of hazard on attenuation and the importance of the use of local attenuation laws in seismic hazard assessment.     

Migration and shortening rates in the northern Apennines,Italy: implications for seismic hazard

Is compression across the northern Apennine fold‐and‐thrust system (Italy) still active? To address this question, we quantified the long‐term rates of migration and shortening of the system along with the measurement errors. Our approach integrates structural geology, seismicity patterns, and statistical treatment of tectonic activity. On the basis of recently published surface and subsurface data, we found a migration rate of 8.85 ± 0.61 mm yr⁻¹. The inception age of individual fold structures follow closely this average rate, indicating that the system has been migrating at a constant rate for the past 17 Myr. Cumulative shortening of the system also increases linearly through time at 2.93 ± 0.31 mm yr⁻¹. The location of the youngest structures in the easternmost portion of the system coincides with a significant peak of seismic moment released by historical earthquakes. We conclude that not only these easternmost thrusts are still active, but also that they generate earthquakes.     

Earthquake slip estimation from the scarp geometry of Himalayan Frontal Thrust, western Himalaya: implications for seismic hazard assessment

Geometric and kinematic analyses of minor thrusts and folds, which record earthquakes between 1200 AD and 1700 AD, were performed for two trench sites (Rampur Ghanda and Ramnagar) located across the Himalayan Frontal Thrust (HFT) in the western Indian Himalaya. The present study aims to re-evaluate the slip estimate of these two trench sites by establishing a link between scarp geometry, displacements observed very close to the surface and slip at deeper levels. As geometry of the active thrust beneath the scarp is unknown, we develop a parametric study to understand the origin of the scarp surface and to estimate the influence of ramp dip. The shortening estimates of Rampur Ghanda trench by line length budget and distance–displacement (D–d) method show values of 23 and 10–15 %, respectively. The estimate inferred from the later method is less than the line length budget suggesting a small internal deformation. Ramnagar trench shows 12 % shortening by line length budget and 10–25 % by the D–d method suggesting a large internal deformation. A parametric study at the trenched fault zone of Rampur Ghanda shows a slip of 16 m beneath the trailing edge of the scarp, and it is sufficient to raise a 8-m-high scarp. This implies that the Rampur Ghanda scarp is balanced with a single event with 7.8-m-coseismic slip in the trenched fault zone at the toe of the scarp, 8–15 % mean deformation within the scarp and 16-m slip at depth along a 30° ramp for a pre-1400 earthquake event. A 16-m slip is the most robust estimate of the maximum slip for a single event reported previously by trench studies along the HFT in the western Indian Himalaya that occurred between 1200 AD and 1700 AD. However, the Ramnagar trenched fault zone shows a slip of 23 m, which is larger than both line length and D–d methods. It implies that a 13-m-high scarp and 23-m slip beneath the rigid block may be ascribed to multiple events. It is for the first time we report that in the south-eastern extent of the western Indian Himalaya, Ramnagar scarp consists of minimum two events (i) pre-1400 AD and (ii) unknown old events of different lateral extents with overlapping ruptures. If the more optimistic two seismic events scenario is followed, the rupture length would be at least 260 km and would lead to an earthquake greater than Mw 8.5.     

Comprehensive seismic hazard assessment of Tripura and Mizoram states

Northeast India is one of the most highly seismically active regions in the world with more than seven earthquakes on an average per year of magnitude 5.0 and above. Reliable seismic hazard assessment could provide the necessary design inputs for earthquake resistant design of structures in this region. In this study, deterministic as well as probabilistic methods have been attempted for seismic hazard assessment of Tripura and Mizoram states at bedrock level condition. An updated earthquake catalogue was collected from various national and international seismological agencies for the period from 1731 to 2011. The homogenization, declustering and data completeness analysis of events have been carried out before hazard evaluation. Seismicity parameters have been estimated using G–R relationship for each source zone. Based on the seismicity, tectonic features and fault rupture mechanism, this region was divided into six major subzones. Region specific correlations were used for magnitude conversion for homogenization of earthquake size. Ground motion equations (Atkinson and Boore 2003; Gupta 2010) were validated with the observed PGA (peak ground acceleration) values before use in the hazard evaluation. In this study, the hazard is estimated using linear sources, identified in and around the study area. Results are presented in the form of PGA using both DSHA (deterministic seismic hazard analysis) and PSHA (probabilistic seismic hazard analysis) with 2 and 10% probability of exceedance in 50 years, and spectral acceleration (T = 0. 2 s, 1.0 s) for both the states (2% probability of exceedance in 50 years). The results are important to provide inputs for planning risk reduction strategies, for developing risk acceptance criteria and financial analysis for possible damages in the study area with a comprehensive analysis and higher resolution hazard mapping.     

Neotectonics and seismic hazard assessment in Hengchun Peninsula,southern Taiwan

Neotectonic data may indicate whether stored elastic energy will be dissipated or released destructively. The Hengchun Peninsula of Taiwan is the southern extremity of the Central Range of Taiwan and thus an emergent part of the accretionary wedge resulting from subduction of Eurasia beneath the Philippine Sea plate at the Manila Trench. Radiocarbon dating of fossil shorelines on the peninsula shows that it has been uplifted at an average rate of 3.8 mm/yr during the Holocene. About $1/3$ of the uplift is due to deformation along the Hengchun reverse fault but, in contrast with the Chelungpu and other low angle reverse faults west of the Central Range, it accommodates strain principally by aseismic creep. To cite this article: C. Vita-Finzi, J.-C. Lin, C. R. Geoscience 337 (2005).     

Modeling and assessment of bridge structure for seismic hazard prevention

This study uses data from Mao-Luo-Hsi Bridge to model the bridge structure and a set of developed alarm and action values to formulate guidelines for bridge maintenance and seismic hazard prevention. The bridge model is improved by incorporating on-site ambient vibration measurement to perform modal analyses. Dynamic analyses of the bridge are implemented using the established 3D model subjected to uniform loading and seismic force, with or without consideration of soil interaction with the structure. The maximum displacements for different sections of the bridge are compared, and statistical regression analyses are used to explore their correlation. Information for bridge safety assessment is proposed, which can mitigate loss of property and lives due to bridge failure. Regression analyses of the maximum displacements between abutments D and E of the considered bridge in the axial, horizontal, and vertical directions under various seismic intensities are conducted, giving R ² values of 0.9462, 0.9352, and 0.9010, respectively. The developed maintenance guidelines are reliable since all parameters from regression analyses have a 95% confidence interval excluding the zero value. The bridge alarm value and action value are determined for this bridge site at earthquake intensity scales of 4 and 5, respectively.     

Probabilistic assessment of seismic hazard of dam sites in Jordan

A Probabilistic method is used to evaluate the seismic hazard of nineteen embankment dam sites in Jordan. A line source model developed by McGuire (1978) is used in this study. An updated earthquake catalogue covering the period from 1 A.D. to 1991 A.D. is used for this purpose. This catalogue includes all earthquakes that occurred in Jordan and adjacent areas, more specifically between latitudes 27.0°–35.5° N and longitudes 32.0°–39.0° E.Nine distinct seismic sources of potential seismic activities are identified. The seismic hazard parameters are determined using the method suggested by Kijko and Sellevoll (1989).The Peak Ground Acceleration (PGA) is selected as a measure of ground motion severity. Esteva (1974) attenuation relationship is used in evaluating PGA values at each dam site. Analysis is carried out for 50%, 90%, and 95% probability that is not being exceeded in a life time of 50, 100, and 200 years.Results of analysis indicate that PGA values are higher for dam sites closer to the Dead Sea Fault. This fault is believed to be responsible for most earthquake activities in Jordan and vicinity. The highest PGA value is found to be for Al-Karama dam site.     

Probabilistic seismic hazard assessment in the northeastern part of Algeria

This work involves updating the evaluation of seismic hazard in Northeast Algeria by a probabilistic approach. This reassessment attempts to resolve inconsistencies between seismic zoning in regional building codes and is further motivated by the need to refine the input data that are used to evaluate seismic hazard scenarios. We adopted a seismotectonic model that accounts for differences in interpretations of regional seismicity. We then performed a probabilistic assessment of regional seismic hazard in Northeast Algeria. Based on a homogeneous earthquake catalog and geological and seismotectonic data gathered in the first part of the study, a seismotectonic zoning map was created and seven risk areas were identified. For each area, peak ground acceleration hazard maps were produced. Details of the calculations are provided, including hazard curves at periods of 0.1, 0.2, 0.33, 0.5, 1.0, and 2.0 s and uniform hazard spectra at urban locations in the area, including Sétif, Constantine, Kherrata, Bejaia, and Jijel.     

Chaotic fault interactions: implications for seismic hazard in New Zealand

A chaotic fault interaction model previously developed for the San Andreas Fault System and the Nankai Trough (examples of transform fault and subduction dominated tectonic regimes, respectively) is here applied to the large-event seismicity in the New Zealand region, where the interacting blocks of the model are taken to be those parts of the Indo-Australian plate boundary that are, from north-east to southwest, subduction dominated, ‘transpressional’, and transform-fault dominated. The model suggests a shorter term recurrence of large events than do simple seismic cycle approaches.     

Multicriteria seismic hazard assessment in Puerto Vallarta metropolitan area,Mexico

Natural Hazards - Puerto Vallarta, a medium-size tourist city, located in the Pacific Coast of Mexico, in a similar way as many other coastal cities, combines human activity with the potential...     

Seismic sources for southern Pakistan and seismic hazard assessment of Karachi

Natural Hazards - Karachi is Pakistan’s largest city with population exceeding 18 million and is amongst the top five most congested cities in the world. Karachi has experienced no earthquake...     

Retreat rates of debris-covered and debris-free glaciers in the Koshi River Basin,central Himalayas,from 1975 to 2010

Debris-covered glaciers are common in the Himalayas and play a key role in understanding future regional water availability and management. Previous studies of regional glacial changes have often neglected debris-covered glaciers or have mixed them with debris-free glaciers. In this study, we generated a new glacier data set that includes debris-covered and debris-free glaciers to study the glacial surface area change in the Koshi River Basin in the central Himalayas. Long time-series Landsat data were used to extract the glacier boundaries using automatic and manual classification methods. The glacial area decreased by 10.4% from 1975 to 2010 at a rate of 0.30% a^?1, with accelerated melting since 2000 (0.47% a^?1). Small glaciers melted faster than large glaciers. In terms of distinctive glacier types, debris-free glaciers shrank at a rate of 0.45% a^?1, faster than debris-covered glaciers (0.18% a^?1), while debris-covered glaciers larger than 5.0 km² retreated at a rate faster than debris-free glaciers of the same-sized group. We also studied the potential interactions between 222 supraglacial lakes and debris-covered glaciers. Debris-covered glaciers with glacial lakes melt faster than glaciers without lakes. This study can improve our understanding of the differences in the changes between debris-covered and debris-free glaciers in the central Himalayas and help evaluate water resource changes in the Himalayas.     

Fuzzy-based method for landslide hazard assessment in active seismic zone of Himalaya

Landslides in Himalaya cause widespread damage in terms of property and human lives. It the present study, an attempt is made to derive information on causative parameters and preparation of landslide-susceptible map using fuzzy data integration in one of the seismically active region of Garhwal Himalaya that was recently devastated by a huge landslide. High-resolution remotely sensed data products acquired from Indian Remote Sensing Satellite before and after the landslide event were processed to improve interpretability and derivation of causative parameters. Spatial data sets such as lithology, rock weathering, geomorphology, lineaments, drainage, land use, anthropogenic factor, soil type and depth, slope gradient, and slope aspect were integrated using fuzzy gamma operator. The final map was reclassified in to five classes such as highly to lowly susceptible classes based on cumulative cutoff. The result shows around 72% of known landslide areas including the large Uttarkashi landslide in the high and very high susceptibility classes comprising of only 37% of the total area. The precipitation data from ground- and satellite-based observations were compared; the precipitation threshold and the role of seismic activity were analyzed for initiation of landslide.     

Estimation of seismic hazard and risks for the Himalayas and surrounding regions based on Unified Scaling Law for Earthquakes

To estimate seismic hazard, the basic law of seismicity, the Gutenberg–Richter recurrence relation, is applied in a modified form involving a spatial term: $\log N\left( {M,\;L} \right) = A - B\left( {M - 5} \right) + C\log L$ , where N(M,L) is the expected annual number of earthquakes of a certain magnitude M within an area of linear size L. The parameters A, B, and C of this Unified Scaling Law for Earthquakes (USLE) in the Himalayas and surrounding regions have been studied on the basis of a variable space and time-scale approach. The observed temporal variability of the A, B, and C coefficients indicates significant changes of seismic activity at the time scales of a few decades. At global scale, the value of A ranges mainly between ?1.0 and 0.5, which determines the average rate of earthquakes that accordingly differs by a factor of 30 or more. The value of B concentrates about 0.9 ranging from under 0.6 to above 1.1, while the fractal dimension of the local seismic prone setting, C, changes from 0.5 to 1.4 and larger. For Himalayan region, the values of A, B, and C have been estimated mainly ranging from ?1.6 to ?1.0, from 0.8 to 1.3, and from 1.0 to 1.4, respectively. We have used the deterministic approach to map the local value of the expected peak ground acceleration (PGA) from the USLE estimated maximum magnitude or, if reliable estimation was not possible, from the observed maximum magnitude during 1900–2012. In result, the seismic hazard map of the Himalayas with spatially distributed PGA was prepared. Further, an attempt is made to generate a series of the earthquake risk maps of the region based on the population density exposed to the seismic hazard.     

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.