Spatiotemporal coda Q variations in the northeastern margin of the Qinghai–Tibet Plateau, China

The seismic quality factor (Q) is an important physical parameter to characterize seismic wave attenuation. Therefore, analyzing its spatiotemporal variation is essential to better understand tectonic activity, characterize earthquake source mechanisms, and assess seismic hazards. In this study, we used a single-scattering model to calculate Q for coda waves (Q_c values) generated by earthquakes with epicentral distances <100 km and magnitudes M > 2.0 recorded in 2000–2023 in the northeastern margin of the Qinghai–Tibet Plateau (the study area). The calculated dependence of Q_c on the bandpass filter central frequency f in the study area was \({Q}_{c}=\left(72.40\pm 9\right){f}^{\left(1.10\pm 0.06\right)}\) $Q_c=\left(72.40,\pm ,9\right)f^{\left(1.10,\pm ,0.06\right)}$ , \({Q}_{c}=\left(100.95\pm 15\right){f}^{\left(1.03\pm 0.07\right)}\) $Q_c=\left(100.95,\pm ,15\right)f^{\left(1.03,\pm ,0.07\right)}$ , and \({Q}_{c}=\left(128.76\pm 20\right){f}^{\left(0.97\pm 0.07\right)}\) $Q_c=\left(128.76,\pm ,20\right)f^{\left(0.97,\pm ,0.07\right)}$ within lapse-time windows of length 20, 30, and 40 s, respectively. To estimate Q_c in distinct active tectonic and fault regions, we divided the study area into two subregions, the Haiyuan and Qinling active tectonic zones. We determined a strong spatial correlation between the Q_c distribution and tectonic activity in the study area, with correspondingly low Q_c values. Finally, by analyzing the temporal evolution of Q_c, we established that nearly all strong earthquakes (M > 6.0) that occurred in the study area in 2000–2023 were preceded by a 10–27% decrease in Q_c values, a phenomenon possibly related to the ‘rock dilatancy’ theory.

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Characteristics of code-wave attenuation in the northeastern margin of the Qinghai–Tibet Plateau.