Passive Seismic Multimethod for Platform Earthquake Investigations (North Russia)

Abstract

The seismic multimethod combines four passive methods based on microseism observations: microseismic sounding method (MSM), passive seismic interferometry (PSI), the horizontal-to-vertical spectral ratio method (HSVR), and microseism activity method (MAM). PSI and HVSR are actively used all over the world for the upper earth's crust studies; MAM and MSM are known in Russia and are used for crustal structure and seismic activity of platform territories. We show what information each of the methods provides, and how they complement each other for upper earth's crust studies. MAM is the new passive method as it allows estimating the amount and location of microcracks (microearthquakes) sources using body waves. MSM is used for detecting vertical inhomogeneities in the crust, HVSR is for horizontal boundaries in upper crust, PSI is for refining the dispersion properties of Rayleigh waves, the results of which are necessary for MSM. We confirm results of passive multimethod with shallow seismic survey. We consider the possibilities of the multimethod using the example of a study of a platform earthquake area. Its location peculiarity is the hard-to-reach region of Russian North where the full-scale active source seismic investigations are impeded. We show the easy observation scheme. At least two three-component broadband seismometers (fixed checkpoint and portable) are required for the sequential passage of the investigated points. The resulting set of seismic data is used for all passive methods included in the multimethod, i.e. there is no need to pass separate profiles for each passive method. The hypocenter damage zone was identified as an intersection of vertical faults and a lateral low-velocity zone in the middle crust near the southern part of the epicentral zone. We established the fluid flows are typical of object.

Keywords: Structure of continental crust, spatial analysis, time-series analysis, seismic interferometry, seismicity and tectonics, seismic noise