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Spatial and temporal b-value anomalies preceding the devastating off coast of NW Sumatra earthquake of December 26, 2004
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.
2005 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 11Article in journal (Refereed) Published
Abstract [en]

[1] Spatial and temporal variations of b values are studied by means of 624 earthquakes in the Andaman-Nicobar Islands region during a five-year period preceding the giant shock on December 26, 2004. Sliding time and space windows containing 50 events are used. Temporal variations reveal two significant drops in b value which coincide with the occurrence of two large shocks (Ms ≥ 7.0) towards the end of 2002 and with the Mw = 9.0 event in 2004. The spatial distribution shows accumulation of stresses (low b) around the epicentres of the 2002 and 2004 events and an event in North Andaman. The area of high stress around the 2004 epicenter extends in NNW-SSE direction over an area about 450 km long.

Place, publisher, year, edition, pages
2005. Vol. 32, no 11
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94500DOI: 10.1029/2005GL022679OAI: oai:DiVA.org:uu-94500DiVA: diva2:168369
Available from: 2006-04-28 Created: 2006-04-28 Last updated: 2017-12-14Bibliographically approved
In thesis
1. The Potential of b-value Variations as Earthquake Precursors for Small and Large Events
Open this publication in new window or tab >>The Potential of b-value Variations as Earthquake Precursors for Small and Large Events
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The potential of variations of b-values in the G-R relation, logN=a-bM as earthquake precursors for small events (rockbursts) in Zinkgruvan mine, Sweden and for tectonic (large) earthquakes in the Andaman-Sumatra region were investigated.

The temporal frequency-magnitude distribution, b(t), of rockbursts in Zinkgruvan mine was examined using high quality data recorded during the period November 1996 to April 2004 with magnitude ranges from Mw= -2.4 to 2.6. A sliding time-window was applied to compute b-values. The windows contain 50 events and were shifted with steps of 5 events. The results indicated that b-values significantly drop preceding rockbursts of magnitude Mw≥1.6.

Temporal and spatial variations of b-values were also examined for tectonic earthquakes, magnitude Mw≥4.1, in the Andaman-Sumatra region. Earthquake data from the ISC, IDC, NEIC and HVRD earthquake catalogs for a period from 01/01/1995 to 12/26/2004 were used for analysis. Spatial variations of b were calculated from circular areas containing 50 events, with nodes on a 0.5° x 0.5° grid. The analysis shows that b(t) estimates using data from different catalogs are comparable and that large earthquakes are preceded by a drop in b(t) of about 0.3~1. The distribution of stress deduced from b-value mapping shows that large earthquakes occurred in the high stress, i.e. low b-value, areas.

Aftershock sequences of the Mw=9, December 26, 2004 and the Mw=8.7, March 28, 2005 shocks were investigated by using the same methods. Results from aftershock sequences show similar behaviour as for the large and presumed independent main events.

The observed variations of b-values with time and in space support the hypothesis that b-values have a precursory potential. The method can be used for a wide range of earthquake magnitude, from microearthquakes (Mw<3) to giant tectonic shocks (Mw~9) and for both of independent shocks and aftershocks.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 46 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 183
Keyword
General, Frequency magnitude distribution, b-values, rockbursts, Andaman-Sumatra region, Zinkgruvan mine, December 26, 2004 earthquake, ALLMÄNT
Identifiers
urn:nbn:se:uu:diva-6885 (URN)91-554-6568-4 (ISBN)
Public defence
2006-05-29, Axel Hambergsalen, Geocentrum, Villavägen 16, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2006-04-28 Created: 2006-04-28Bibliographically approved

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Kulhanek, OtaPersson, Leif

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