<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>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6885 |
| Date | January 2006 |
| Creators | Nuannin, Paiboon |
| Publisher | Uppsala University, Department of Earth Sciences, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 183 |
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