Seismic hazard evaluation of Nepal region: a particular emphasis on 2015 Gorkha earthquake scenario
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Abstract The tectonic collision between the Indian and Eurasian plates since 50 million years is responsible for creating the Nepal Himalayan zone as part of the whole Himalayan orogeny belt. As a result of this collision, major changes and deformation in Earth have been evolving through ongoing stress build-up and release. In this study, an overview of the stress distribution has been made by using the Frequency-magnitude relation across the Nepal Himalayan region, which is supported by an extensive analysis of b-values and their spatiotemporal variations. Abruptly the whole region is being divided into four sub-regions. The consequences of b-value changes have been thoroughly examined for a better and minute analysis of the present-day hazardous scenario of this Nepal Himalayan region. Two highly stressed areas have been observed in Nepal's eastern and westernmost parts by interpreting the b-values. The depth sections of the b-value are estimated across the two zones revealing that these stress-accumulated regions are increasing in depth with an increase in latitude towards the north. A moderately stressed area was also found, which is concentrated mainly around the MCT fault in the western part. A particular emphasis on the 2015 Gorkha region has been carried out to analyze this region's pre- and post-earthquake scenarios and stress patterns. The analysis revealed that most of the stress released by the Gorkha earthquake was concentrated in the western side of the event, whereas the eastern side was still moderately stressed.Keywords:
Orogeny
Collision zone
Orogeny
Collision zone
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Moment magnitude scale
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Seismic reflection profiles, petroleum wells, and relocated earthquakes reveal the presence of an active blind-thrust fault beneath metropolitan Los Angeles. A segment of this fault likely caused the 1987 Whittier Narrows (magnitude 6.0) earthquake. Mapped sizes of other fault segments suggest that the system is capable of much larger (magnitude 6.5 to 7) and more destructive earthquakes.
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Studies of the properties of seismogenic structures play an important role in delineation of potential earthquake source and in determination of parameters of seismic activity. The location, direction, size and the maximum potential earthquake magnitude of a seismogenic structure can be used separately to determine the location, direction, extent and upper limit magnitude of the related potential earthquake sources. The recurrence behavior of large earthquakes on seismogenic structures is closely related to the estimation of the annual average occurrence of the high magnitude grade earthquakes. In consideration of the spatial heterogeneity of seismicity, two grade delineation of potential earthquake source has been adopted in seismic hazard assessment in China since the late 1980s. Moreover, a relatively large region is usually taken as the seismictiy statistical unit (seismic region or seismic zone) in order to gain sufficient seismic data, so that it might contain some seismotectonic blocks with different background earthquake magnitudes. For the sake of more reasonable seismic hazard assessment, it is necessary to consider these seismotectonic blocks as the second grade potential earthquake sources, which are then subdivided into the third grade potential earthquake sources. On the basis of research on the recurrence behavior of large earthquakes on seismogenic structures, this paper proposes a method for calculating the annual average occurrence of the high magnitude grade earthquakes by applying the equivalent probability transferring in the predicted time scale. This method may greatly enhance the reasonability of seismic risk assessment. The frequency insufficiency of the second grade magnitude earthquakes of potential earthquake sources and the spatial inhomogeneity of seismogenic structures, as well as their applications to determining the parameters of potential earthquake sources are also discussed in this paper.
Earthquake simulation
Seismic risk
Seismic microzonation
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abstract Aftershocks following the Ceres earthquake of September 29, 1969, (Magnitude 6.3) were monitored using a number of portable seismic recording stations. Earthquakes of this magnitude are rare in South Africa. The event occurred in a relatively densely-populated part of the Republic, and resulted in nine deaths and considerable damage. Accurate locations of some 125 aftershocks delineate a linear, almost vertical fault plane. The volume of the aftershock region is 3 × 9 × 20 km3 with the depth of the aftershocks varying from surface to 9 km. Aftershocks following the September event had almost ceased when another large earthquake (Magnitude 5.7) occurred on April 14, 1970. Following this event, the frequency and magnitude of aftershocks increased, and they were located on a limited portion of the same fault system delineated by the September 29th aftershocks. Previously-mapped faults do not correlate simply with the fault zone indicated by the aftershock sequence.
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Moment magnitude scale
Seismometer
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The tectonic setting of Aceh is very interesting to be studied. Despite many researches of Aceh’s tectonic setting, still there are many hidden faults waiting to be studied. One of them is Lokop-Kutacane fault which becomes active in 2020. There is an increase in frequency of earthquakes in Lokop-Kutacane fault. Magnitude-fault length analysis indicates that maximum magnitude of Lokop-Kutacane fault is M7,6 but historically it only had M6.8 in the past. CDF and PDF analysis show that the highest probability of earthquake magnitude is between 3 to 4 at 28.9%. Focal mechanism also gives two nodal planes with the direction of strike of 62 and 153. The distribution of earthquakes trend fits the 153 strike nodal plane with the direction of Northwest-Southeast. The calculation of b-value gives 0.78 that indicate that the fault is not able to hold a large amount of stress or the stress will be released in form of small to moderate earthquakes.
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