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The Qp attenuation structure of the Koyna-Warna region, Maharashtra India, and its correlation to seismicity

Kumar Sanjay, Kumar Prakash, Kumar Sai Vijay

Acta Geophysica

2023

Vol. 71, no. 6

2603--2618

In this study, we developed a three-dimensional (3D) (Qp) P-wave attenuation model of the uppermost crust (0-10 km depth) of the Koyna-Warna region (India). The inversion of attenuation operator (t*) is used to deduce a 3D Qp attenuation model using simul2000 code by assuming that t* is independent of frequency. A total of 276 earthquakes (1.0 ≤ ML ≤ 3.5) were used for this study, those providing 2045 t* values. The t* values are determined by fitting the observed P-wave amplitude spectrum with the theoretical spectrum by assuming an ω2 source model using a nonlinear least squares spectral-fitting algorithm. The tomography model shows the low Qp anomalies (~ 200-350) at shallow depth (0-3 km) that could be related to fracturing and cracks. The Qp value gradually increases with depth due to the closure of cracks and fractures as pressure increases from the lithostatic load. The high Qp (~ 500-600) are found in the intense seismic activity zone at 5-7 km depth where majority of the earthquakes were generated corresponds to the brittle crust and well correlated to higher Vp (~ 5.5-6.0 km/s) reported previously in the study area. We inferred that the high Qp is well correlated to seismicity likely associated with the dry to partially saturated rocks, which playing a vital role in the genesis of earthquakes in the study area.

Numerical support of laboratory experiments: Attenuation and velocity estimations

Saenger E., Madonna C., Almqvist B.

Acta Geophysica

2014

Vol. 62, no. 1

1--11

We show that numerical support of laboratory experiments can significantly increase the understanding and simplify the interpretation of the obtained laboratory results. First we perform simulations of the Seismic Wave Attenuation Module to measure seismic attenuation of reservoir rocks. Our findings confirm the accuracy of this system. However, precision can be further improved by optimizing the sensor positions. Second, we model wave propagation for an ultrasonic pulse transmission experiment used to determine pressure- and temperature-dependent seismic velocities in the rock. Multiple waves are identified in our computer experiment, including bar waves. The metal jacket that houses the sample assembly needs to be taken into account for a proper estimation of the ultrasonic velocities. This influence is frequency-dependent.