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- Amini, Samar
(författare)
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Source analysis of multiplet earthquakes (two case studies in Iran)
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multiplet earthquakes are large earthquakes of similar magnitude which occur close in time in the same limited geographical area. They are not common but they considerably increase the potential hazard in the area in which they occur. This thesis studies source properties and triggering mechanisms of two sets of multiplet events in Iran, which both occurred in unexpected areas, but close to some major active fault systems. The first multiplet is an earthquake doublet (Mw 6.5 and Mw 6.4) which occurred in northwestern Iran and caused more than 300 fatalities and significant injuries. In paper I, a teleseismic body-waveform inversion was used to deduce the slip distribution pattern on the fault plane of the first mainshock. The estimated slip pattern was utilized to calculate the Coulomb stress changes on the second fault plane and on the following aftershocks. Based on this analysis, the ambiguity between the primary and auxiliary fault plane of the second mainshock could be resolved. The second set of events is a triplet (Mw 6.1 - 6.0) that occurred in eastern Iran, close to the Kerman province. In paper II, the rupture propagation patterns of the three mainshocks were analyzed using Empirical Green’s Function (EGF) deconvolution. Two different approaches were used: One, the analysis of the azimuthal variation of the apparent rupture duration based on the width of the observed relative source time functions, and the second, the analysis of along-strike rupture directivity by assessing azimuthal variations of the relative amplitude spectra. The second approach was also used to investigate the rupture directivity of the largest aftershocks in the sequence (Mw 5 - 5.5). A clear tendency for rupture propagation towards the northwest was observed for the sequence, which suggests that the regional stress field has a central role in controlling the rupture propagation direction. In paper III, the slip distribution patterns of the triplet earthquakes were analyzed using teleseismic body-waveform inversion, and the similarities and differences in the rupture processes of the three mainshocks were investigated. Using the Coulomb stress analyses, the stress interactions between the mainshocks were examined, leading to identification of the primary and auxiliary planes. Finally, we suggest that the hazard estimates in complex continental regions such as Iran need to consider the probability of multiplets, which might allow a reduction of the seismic risk associated to the occurrence of further large earthquakes subsequent to a devastating earthquake.
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| 2. |
- Joshi, Niranjan
(författare)
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Bias-adjusted analysis of global natural disaster records and an assessment of seismic hazard in Sweden
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Natural disasters pose significant challenges today and demand efficient allocation of society’s limited resources for disaster risk reduction. This relies on analysis of natural disaster records, which are prone to (reporting) biases that can affect the inferences drawn from their analysis. Data incompleteness is common in earthquake seismology, and, with a starting point in the Gutenberg-Richter law, this thesis studies the power-law behaviour between fatalities and the frequency of global natural disasters recorded by EM-DAT from 1900 to 2020. Analysing, first, the power-law behaviour of global earthquake frequency and magnitude reveals overlapping patterns, and apparent improved reporting completeness over the studied periods, implying any increase in recorded earthquakes is a reporting artefact. Similarly, “frequency-magnitude” analysis of earthquake disasters shows power-law behaviour and an almost-unchanged distribution of fatalities over time, which also implies improved reporting. Similar analysis of hydro-meteorological disasters in EM-DAT shows their substantially increased number with time to be a reporting artefact driven by improved reporting of low-fatality disasters. The increasing gradient of the power-law part of the frequency-magnitude graphs implies that the worst events have become less fatal on average. Climate-related disaster risk reduction actions have thus been very successful, resulting in a continuous decline in aggregate associated fatalities, to the extent that earthquakes have been the most fatal natural disasters over the last few decades. Notably, while the earthquake magnitude distribution is dominated by earthquakes in high-seismicity zones, fatalities predominantly occur in low-seismicity intraplate regions. This implies that seismic hazard in Sweden, an intraplate area, may be significant, especially as earthquakes as large as M8 have occurred in its recent deglaciation phase. Hazard analysis based on data from the recently expanded Swedish seismic network clearly unveils significant hazard posed by Post-Glacial faults in the North. This research advances our understanding of natural disaster dynamics, emphasizing the necessity for non-conventional methodologies to analyze historical data. It offers important insights to help form effective disaster risk reduction strategies, particularly in the context of seismic hazard assessment for specific regions like Sweden.
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