Source parameters and three‐dimensional attenuation structure from the inversion of microearthquake pulse width data: Method and synthetic tests

Abstract

Abstract. We propose a new method to determine source parameters and attenuation structure of a three-dimensional medium based on first P rise time and total pulse width measurements from microearthquake data. The effects of fault finiteness on seismic radiation are taken into account by assuming the rupture model for a circular crack of Sato and Hirasawa (1973). Ray theory synthetic seismograms in a constant Q anelastic medium are computed to derive a set of nonlinear equations which relate the source and attenuation parameters (fault radius, orientation of the fault plane, and quality factor) to the pulse width data (half and total duration of the P waveforms).The numerically built relationships are used to compute the direct problem in the framework of a nonlinear inversion scheme, based on the modified downhill Simplex method. The validity and robustness of the inversion method are tested by synthetic simulations by assuming the sources and receivers configuration of the seismic passive experiment conducted in the Campi Flegrei caldera (southern Italy) during the last microearthquake crisis (1982)(1983)(1984). Different heterogeneous Q models have been considered in order to assess the uncertainty and resolution of source and attenuation parameters for the given acquisition layout. The results of this simulation study indicate that first pulse width data from a local network permit retrieval with sufficient accuracy of the heterogeneous Q structure and fault radii. A rather dense azimuthal coverage of the sources is instead needed to recover the angles (in particular, the fault strike) which define the fault orientation.

Fault plane orientations of small earthquakes of the 1997 Umbria-Marche (Italy) seismic sequence fromP-wave polarities and rise times

“…This phenomenon, known as the directivity source effect, has been theoretically explained in terms of both the spatial finiteness of the seismic source and its finite rupture velocity (e.g. Zollo & de Lorenzo 2001): It has been demonstrated (Boatwright 1984) that the directivity source effect depend also on the shape of the fractured area (unilateral, circular or mixed).…”

“…We propose an improvement of the inversion method of Zollo & de Lorenzo (2001) to account for a priori information on dip and strike. With respect to the previous study, the imposition of (δ, φ) allows us to reduce the number of unknown model parameters from four (L, δ, φ and Q p ) to only two (L and Q p ).…”

Determination of Internal Structure of Semeru Volcano Based on Seismic Attenuation Imagery

“…Pencitraan dari Qfactor dapat digunakan untuk menentukan lokasi dan extension of magma bodies pada daerah vulkanik dan detail kontribusi fluida pada daerah patahan maupun berdasarkan pada tingginya porositas efektifnya [4,5]. Selain itu sebenarnya nilai Q-factor juga dapat digunakan sebagai indikator adanya hidrokarbon dan panas bumi [6,7].…”

Intrinsic Qp seismic attenuation from the rise time of microearthquakes: a local scale application at Rio‐Antirrio, Western Greece

“…Obviously, the most limiting assumption of this method is that it neglects the directivity effect of the seismic radiation generated by a finite dimensional seismic source (Zollo and De Lorenzo 2001; Tselentis et al 2009). The directionality of the source will have a limited effect as long as it only affects the amplitude of the signal and not the spectral content.…”

“…Several investigations in geothermal areas (Zucca, Hutchings and Kasameyer 1994; Sanders and Nixon 1995; Sanders et al 1995; Wu and Lees 1996; Zollo and De Lorenzo 2001) have shown that the imaging of the quality factor Q is a useful tool to define location and extension of magma bodies in volcanic areas and to detail the fluid contribution through fracture systems. Usually, a high degree of cracking or high effective porosity (Zucca et al 1994; Sanders et al 1995) and the presence of water/gas in the fractures lower Q p values.…”