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Spatiotemporal characteristics of aftershock sequences in the south Iceland seismic zone: Interpretation in terms of pore pressure diffusion and poroelasticity
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2010 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 183, no 3, 1104-1118 p.Article in journal (Refereed) Published
Abstract [en]

In seismology numerous observations indicate a relationship between pore pressure in the Earth's crust and the occurrence of earthquakes. In this paper we study aftershock sequences in the South Iceland Seismic Zone (SISZ), where poroelastic rebound has been observed in the post-seismic period of two M 6.5 earthquakes in 2000 June. We analyse characteristic features in the spatiotemporal distribution of aftershocks following the two M 6.5 2000 June 17 and 21 earthquakes and a M 4.5 earthquake on 1999 September 27. These features include an initial pre-power-law decay period characterized by an initially finite aftershock rate, a subsequent power-law decay interrupted by distinct and temporary rate increases and decreases as well as increased clustering of aftershocks with time in the main shock fault zones. Extending the analysis to a M 3.2 aftershock sequence in the same region confirms an increase in the duration of the initial pre-power-law decay period with increasing main shock magnitude. We find, from the return time of aftershock magnitudes to the long-term completeness level, that the initial pre-power-law decay period and its durational dependence on main shock magnitude may not only represent incompleteness artefacts but may also reflect the physics of the aftershock process in the SISZ. Based on pore pressure diffusion modelling, we interpret the origin of the observed SISZ aftershock features in terms of a spatially non-linear coseismic influence of the main shock on stresses in the surrounding crust and poroelastic adjustment of stresses and pore pressures during main shock initiated diffusion processes. In a discussion of alternative interpretations, we find that rate and state friction and dynamically propagating crack models, the statistical ETAS model, afterslip models, viscoelastic relaxation of the lower crust and upper mantle and a recently proposed dependence on the crustal state of stress all appear inconsistent with at least one of the characteristic spatiotemporal features of the studied SISZ aftershock sequences. We conclude that these features constitute strong evidence for pore pressure effects in aftershock triggering within the SISZ and recommend that poroelastic adjustment of stresses is taken into account in modelling of main shock initiated pore pressure diffusion.

Place, publisher, year, edition, pages
2010. Vol. 183, no 3, 1104-1118 p.
Keyword [en]
Geomechanics, Mechanics, theory and modelling, Seismic cycle, Seismicity and tectonics, Spatial analysis, Time series analysis
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97976DOI: 10.1111/j.1365-246X.2010.04812.xISI: 000284274700003OAI: oai:DiVA.org:uu-97976DiVA: diva2:173121
Available from: 2009-01-21 Created: 2009-01-21 Last updated: 2017-01-25Bibliographically 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

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