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Bias-adjusted analysis of global natural disaster records and an assessment of seismic hazard in Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Seismologi)ORCID iD: 0000-0002-6337-7839
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2024. , p. 73
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2347
Keywords [en]
Power-law, Natural-disasters, Seismic-hazard assessment.
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-517257ISBN: 978-91-513-1985-8 (print)OAI: oai:DiVA.org:uu-517257DiVA, id: diva2:1817357
Public defence
2024-03-01, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2024-02-07 Created: 2023-12-06 Last updated: 2024-02-07
List of papers
1. Earthquake disaster fatality data: Temporally stable power-law behavior and effects of underreporting
Open this publication in new window or tab >>Earthquake disaster fatality data: Temporally stable power-law behavior and effects of underreporting
(English)In: Seismological Research Letters, ISSN 0895-0695, E-ISSN 1938-2057Article in journal (Refereed) Submitted
Abstract [en]

We investigate changes in the global reported fatalities from earthquake disasters in theleading global disaster database EM-DAT. Drawing parallels with the Gutenberg-Richterfrequency-magnitude analysis, in terms of disaster frequency versus the number of casual-ties, we see a significant overlap of the curves and improving levels of completeness oversix 20-year periods. This implies a decrease in underreporting with time. We find that theapparent strong upwards trend in the number of (reported) earthquake disasters in EM-DATis caused by a gradually improved reporting primarily of events killing fewer than 10 peo-ple. An implication of our findings is that the true (reported and unreported) number ofearthquake disasters, according to the EM-DAT definition, has been surprisingly constantover, at least, the last 100 years. We also show that the average annual number of peoplekilled in earthquake disasters is relatively unaffected by spurious trends in reporting, and hasremained remarkably constant, at least since the 1960s, despite population increase.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-517254 (URN)
Available from: 2023-12-06 Created: 2023-12-06 Last updated: 2023-12-13
2. Incompleteness of natural disaster data and its implications on the interpretation of trends
Open this publication in new window or tab >>Incompleteness of natural disaster data and its implications on the interpretation of trends
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We use data from a leading global database, primarily the reported numbers of disasters of different types and associated fatalities, to elucidate long-term trends in natural disaster impact. There are very strong upward trends in the number of reported disasters. However, we show that these trends are strongly biased by progressively improving reporting. Applying established methods based on analysing evolving differences in the patterns of large (many fatality) to small (fewer fatality) events can be used to compensate for this bias. For all disaster types investigated the long-term (multi-decade) true number of disasters appears to be unexpectedly stable over time, albeit with a significant temporary increase 1980-90. However, the corresponding numbers for the total number of fatalities from the weather-related disasters have declined strongly, due to very effective mitigation for  larger disasters. Data for the recent decades shows a systematic decrease in the number of larger (more fatality) disasters compared to smaller. In contrast, for the geophysical disasters, predominantly earthquakes, the relative numbers of larger versus smaller disasters is fairly constant, as are total fatalities.

National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-517255 (URN)
Available from: 2023-12-06 Created: 2023-12-06 Last updated: 2023-12-13
3. Probabilistic Seismic Hazard Assessment of Sweden
Open this publication in new window or tab >>Probabilistic Seismic Hazard Assessment of Sweden
(English)In: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981Article in journal (Refereed) Submitted
Abstract [en]

Assessing seismic hazard in stable continental regions (SCR) such as Sweden poses unique challenges compared to active seismic regions. With diffuse seismicity, low seismicity rate, few large magnitude earthquakes and little strong motion data, estimating recurrence parameters and determining appropriate attenuation relationships is challenging. This study presents a probabilistic seismic hazard assessment of Sweden based on a recent earthquake catalogue which includes a large number of events with magnitudes ranging from 5.9 to -1.4, enabling recurrence parameters to be calculated for more source areas than in previous studies, and with less uncertainty. Recent ground motion models developed specifically for stable continental regions, including Fennoscandia, are used in logic trees accounting for their uncertainty and the hazard is calculated using the OpenQuake engine.The results are presented in the form of mean peak ground acceleration (PGA) maps at 475 and 2500 year return periods and hazard curves for four seismically active areas in Sweden. We find the highest hazard in the northernmost part of the country, in the post-glacial fault province. This is in contrast to previous studies, which have not considered the high seismic activity on the post-glacial faults. We also find relatively high hazard along the northeast coast and in southwestern Sweden, whereas the southeast and the mountain region to the northwest have low hazard.For a 475 year return period we estimate the highest PGAs to be 0.04-0.05g, in the far north, and for a 2500 year return period it is 0.1-0.15g in the same area. Significant uncertainties remain to be addressed in regards to the SCR seismicity in Sweden, including the homogenization of small local magnitudes with large moment magnitudes, the occurrence of large events in areas with little prior seismicity and the uncertainties surrounding the potential for large earthquakes on the post-glacial faults in northern Fennoscandia.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-517256 (URN)
Available from: 2023-12-06 Created: 2023-12-06 Last updated: 2023-12-06

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