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The Potential of <i>b</i>-value Variations as Earthquake Precursors for Small and Large Events

<p>The potential of variations of <i>b-</i>values in the G-R relation, log<i>N=a-bM</i> as earthquake precursors for small events (rockbursts) in Zinkgruvan mine, Sweden and for tectonic (large) earthquakes in the Andaman-Sumatra region were investigated. </p><p>The temporal frequency-magnitude distribution, <i>b(t)</i>, of rockbursts in Zinkgruvan mine was examined using high quality data recorded during the period November 1996 to April 2004 with magnitude ranges from <i>M</i><i>w</i>= -2.4 to 2.6. A sliding time-window was applied to compute <i>b</i>-values. The windows contain 50 events and were shifted with steps of 5 events. The results indicated that <i>b</i>-values significantly drop preceding rockbursts of magnitude <i>M</i><i>w</i>≥1.6.</p><p>Temporal and spatial variations of <i>b</i>-values were also examined for tectonic earthquakes, magnitude <i>M</i><i>w</i>≥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 <i>b</i> were calculated from circular areas containing 50 events, with nodes on a 0.5° x 0.5° grid. The analysis shows that <i>b(t)</i> estimates using data from different catalogs<i> </i>are comparable and that large earthquakes are preceded by a drop in <i>b(t)</i> of about 0.3~1. The distribution of stress deduced from <i>b</i>-value mapping shows that large earthquakes occurred in the high stress, i.e. low <i>b</i>-value, areas.</p><p>Aftershock sequences of the <i>M</i><i>w</i>=9, December 26, 2004 and the <i>M</i><i>w</i>=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.</p><p>The observed variations of <i>b</i>-values with time and in space support the hypothesis that <i>b</i>-values have a precursory potential. The method can be used for a wide range of earthquake magnitude, from microearthquakes (<i>M</i><i>w</i><3) to giant tectonic shocks (<i>M</i><i>w</i>~9) and for both of independent shocks and aftershocks.</p>

Identiferoai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6885
Date January 2006
CreatorsNuannin, Paiboon
PublisherUppsala University, Department of Earth Sciences, Uppsala : Acta Universitatis Upsaliensis
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, text
RelationDigital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 183

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