סמינר מיוחד בחוג לגיאופיזיקה

Title:

Wind-induced signals and noise in seismological records – Interdisciplinary measurements at the Dead Sea to investigate the impact of wind on ground motion velocity

Abstract:

Atmospheric processes, ranging from microscale turbulence to severe storms on the synoptic scale, impact the continuous ground motion of the earth and have the potential to induce strong broadband noise in seismological recordings. In the scope of the DESERVE project we designed and conducted a target-oriented experiment to quantify the influence of wind on ground motion velocity in the Dead Sea valley. For the period from March 2014 to February 2015 a seismological array, consisting of 15 three-component short-period and broad-band stations, was operated near Madaba, Jordan, complemented by one meteorological tower providing synchronized, continuous threecomponent measurements of wind speed.

Results reveal a pronounced, predominantly linear increase of the logarithmic power of ground motion velocity with rising mean horizontal wind speed at all seismological recording stations. The measurements in rough, mountainous terrain further identify a strong dependency of wind-induced noise on the area overflown, and therefore demonstrate the necessity to consider topography or surface characteristics as well. In order to assess the noise level of seismological recordings with respect to a dynamically changing wind field, we develop a methodology to account for the dependency of power spectral density of ground motion velocity on wind speed and wind direction for long, statistically significant periods. We further find that the turbulent wind field, respectively the friction velocity, in addition to the mean wind flow, indicates the shear stress acting on the ground coinciding with wind-induced noise in seismological records.

מארגן הסמינר: פרופ' איל חפץ