SIMULATION OF THE ROCK SURFACE LUMINESCENCE SIGNALS ON BEDROCK FAULT SCARPS BY STICK-SLIP AND CREEP MOVEMENTS
The reconstruct of the stick-slip and creep histories is essential for understanding fault activities and seismic hazard assessment.Distinguishing stick-slip and creep using geodetic technology has become a hot research area in recent years,but distinguishing and estimating seismic slip and creep on geological timescales(e.g.,over hundreds of years)is challenging due to the lack of historical,geodetic and remote sensing data extending back more than a few hundred years.This study uses a newly developed dating technique(rock surface optically-stimulated-luminescence(OSL)dating)combined with the OSL decay parameters of granite samples from the Langshan fault in Inner Mongolia to simulate optically stimulated OSL-depth curves and depths of half saturation of luminescence signal under various scenarios such as fault seismic slipping,creeping,and erosion of colluvial wedge.The study compares these OSL-depth profiles,especially the depths of the half saturation,under different slipping modes,and summarizes their features.During fault seismic slip,samples at different heights along the fault scarp display a"step-like"distribution pattern at their depths of half saturation.While during creep,however,they exhibit a"slope-like"pattern.Such differences may lie in that the slope during accelerating creeping is steeper than the slope during constant-speed creeping.Correspondingly,the resolution of residual luminescence-depth profile and depth of half saturation is also higher during accelerating creeping.During intra-earthquake creep events between seismic slip occurrences on the bedrock fault scarp,the distribution of half-saturation depth in the samples includes segments resembling both"steps"and"slopes",which indicate the seismic slip and creep activities of the fault respectively.If the samples at the base of the colluvial wedge have had a sufficiently long last exposure time,the luminescence-depth profile and half-saturation depth distribution due to the erosion of the colluvial wedge would be approximately the same as in the three-phase seismic slip scenario.This indicates that samples previously buried by the colluvial wedge may be considered within the seismic displacement.Conversely,if the last exposure time of the base samples at the base of the colluvial wedge is short,the bleaching depth of the luminescence signal of these base samples will be noticeably shallower than that of the other samples within the seismic displacement,indicating the observed erosion of the colluvial wedge in this case.Furthermore,the seismic displacement ideally should include the buried location of the colluvial wedge.Therefore,when the luminescence curves and half-saturation depth distributions fail to identify the presence of the colluvial wedge,it is acceptable to include the buried location of the colluvial wedge in the seismic displacement calculation.Conversely,the luminescence-depth curves and half-saturation depth distributions document the erosion caused by the colluvial wedge.The simulation results demonstrate that this method can effectively distinguish between fault slipping and creeping,obtain corresponding displacements,and potentially record the erosion of colluvial wedge.This study also analyzes the temporal resolution of the method for distinguishing fault activity times and the spatial resolution for quantifying displacements.The specific situation is as follows.When exposure age of the bedrock fault scarp is within a thousand years,the rock surface OSL dating method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval of hundreds of years.When exposure age of the bedrock fault scarp is in the range of 100-101ka,the method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval exceeding a thousand years.When exposure age of the bedrock fault scarp is over ten-thousand years,the resolution of this method may be significantly reduced.The spatial resolution of seismic displacements using this method depends on interval between sampling and testing samples,typically in 10～30cm.
Bedrock normal fault scarpstick-slipcreeprock surfaceoptical stimulated luminescence dating
万方数据
维普
