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Earthquakes descaled: on waiting time distributions and scaling laws
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
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2005 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 10, 108501- p.Article in journal (Refereed) Published
Abstract [en]

Recently, several authors have used waiting time distributions for large earthquake data sets to draw conclusions regarding the physics of earthquake processes. We show, theoretically and by simulation, that a characteristic kink in observed waiting time distributions does not have the physical significance of separating correlated and uncorrelated earthquakes. It also follows from our discussion that the Omori law is not trivially related to a proposed scaling law and that caution must be taken before the spatial scaling exponent of the law is interpreted as a fractal dimension of seismicity.

Place, publisher, year, edition, pages
2005. Vol. 94, no 10, 108501- p.
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97973DOI: 10.1103/PhysRevLett.94.108501PubMedID: 15783532OAI: oai:DiVA.org:uu-97973DiVA: diva2:173118
Available from: 2009-01-21 Created: 2009-01-21 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Physics of Aftershocks in the South Iceland Seismic Zone: Insights into the earthquake process from statistics and numerical modelling of aftershock sequences
Open this publication in new window or tab >>Physics of Aftershocks in the South Iceland Seismic Zone: Insights into the earthquake process from statistics and numerical modelling of aftershock sequences
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In seismology, an important goal is to attain a better understanding of the earthquake process. In this study of the physics of aftershock generation, I couple statistical analysis with modelling of physical processes in the postseismic period. I present a theoretical formulation for the distribution of interevent times for aftershock sequences obeying the empirically well established Omori law. As opposed to claims by other authors, this work demonstrates that the duration of the time interval between two successive earthquakes cannot be used to identify whether or not they belong to the same aftershock sequence or occur as a result of the same underlying process. This implies that a proper understanding of earthquake interevent time distributions is necessary before conclusions regarding the physics of the earthquake process are drawn.

In a discussion of self-organised criticality (SOC) in relation to empirical laws in seismology, I find that Omori's law for aftershocks cannot be used as evidence for the theory of SOC. Instead, I consider that the occurrence of aftershocks in accordance with Omori's law is a result of a physical process that can be modelled and understood.

I analyse characteristic features in the spatiotemporal distribution of aftershocks in the south Iceland seismic zone, following the two M6.5 June 2000 earthquakes and a M4.5 earthquake in September, 1999. These features include an initially constant aftershock rate, whose duration is larger following a larger main shock, and a subsequent power law decay that is interrupted by distinct and temporary deviations in terms of rate increases and decreases. Based on pore pressure diffusion modelling, I interpret these features in terms of main shock initiated diffusion processes. I conclude that thorough data analysis and physics-based modelling are essential components in attempts to improve our understanding of processes governing the occurrence of earthquakes.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2009. 128 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 592
Keyword
Earthquake processes, Aftershocks, Physics of aftershocks, Omori law, Postseismic processes, Pore pressure diffusion, Poroelasticity, Statistical seismology, Self-organised criticality, Interevent time distributions, Waiting time distributions
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-9531 (URN)978-91-554-7394-5 (ISBN)
Public defence
2009-02-13, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2009-01-21 Created: 2009-01-21 Last updated: 2016-05-13Bibliographically approved
2. Studies of Unusual Seismicity and Long Period Events at the Glacier Overlain Katla Volcano, Iceland
Open this publication in new window or tab >>Studies of Unusual Seismicity and Long Period Events at the Glacier Overlain Katla Volcano, Iceland
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Earthquake catalogues are usually dominated by diffusive behaviour consistent with the Omori law of aftershocks. This is investigated in terms of waiting times, i.e. the time between successive events in a time-sorted earthquake catalogue. The theoretical waiting time probability distribution for the Omori law is derived and shown to predict the numerically produced Omori aftershock sequence well. These results enhance our understanding of aftershock processes and demonstrate that previous waiting time interpretations were severely flawed.

Iceland earthquake catalogues are studied in terms of waiting times. Omori aftershock sequences are shown to predict most datasets well but there are some significant exceptions. One of these is data from the glacier covered Katla volcano in South Iceland, with few aftershocks. This dataset can be further split into two geographical groups: Several hundred volcano-tectonic earthquakes occurring within the caldera, reaching depths down to 15 km, and thousands of emergent low frequency earthquakes with a poorly defined shallow source in Goðabunga, in the western part of Katla. These events are investigated further.

The lp events at Goðabunga have been recorded for decades and show a clear seasonal and climate-related correlation where their number increases in the autumn as well as during warmer years. Many of them form groups with very with similar waveforms. New broad-band seismic data suggests that the lp events originate in a steep outlet glacier covering Katla. Here, ice movement leads to ice falls over the steep escarpment, and we now believe that the lp events are generated by large ice falls rather than being related to gas or magma movements within the volcano, and are not precursors to an eruption as previously suspected. This observation probably has major significance for hazard estimation at the many ice-covered volcanoes around the world.

We report near-field (vlp) signals simultaneous with the largest lp events. Our data is partly consistent in character with surface deformation (displacement and tilt) due to the ice movements. However, in line with results from elsewhere, the magnitudes of the observed effects are large relative to those from mathematical modelling. Our analysis suggests that the signal is not an instrumental artefact. Possible explanations are discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 636
National Category
Geophysics
Research subject
Geophysics Specialized In Seismology
Identifiers
urn:nbn:se:uu:diva-100771 (URN)978-91-554-7500-0 (ISBN)
Public defence
2009-05-08, Hambergssalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2009-04-16 Created: 2009-04-07 Last updated: 2009-04-27

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