Mutual Coupling Between Meteorological Parameters and Secondary Microseisms

Abstract

The basic scientific question of this study was: do other mechanisms exist for excitation of secondary microseisms aside from the widely accepted mechanism by non-linear interactions of respective ocean waves. Here we use continuous broadband data from secondary microseisms recorded at the Ostrava-Krásné Pole, Czech Republic (OKC) seismic station to create a massive seismological database. Except for seismological data, various meteorological features and their mutual relations were analysed: temperature, the so called "shifted" temperature, air density, changes of atmospheric pressure, and synoptic situations. These analyses prove that maximum amplitudes of microseisms were observed during winter, while minimum amplitudes occured in summer months. The annual variations of microseisms amplitudes could not be explained by annual variations of storm activity above the North Atlantic. In addition, current analyses also aim at quantitative and quantitative evaluation of synoptic situations for triggering individual microseismic anomalies. Some of the meteorological features, namely the distribution of low pressures above northern Europe and high-pressure areas in Central Europe make it easy to explain most of the microseismic extremes. Here we pay special attention to the influence of large earthquakes, which usually induce slow deformation waves. We conclude that at least three mechanisms of microseism generation are possible: (1) the function of atmospheric pressure at sea level in the North Atlantic, (2) the effects of spreading of thermoelastic waves in the rock mass and (3) deformation waves induced by large earthquakes.

The Possible Explanation for Secondary Microseisms Seasonal and Annual Variations

“…It can be stated that the excitation of secondary microseisms due to windstorms above the ocean is not the necessary condition for their excitation but represents only a triggering mechanism. Similarly, the third triggering mechanism connected with deformation waves after catastrophic earthquakes shows the same background as this process, i.e., excitation of secondary microseisms after catastrophic earthquakes in summer is relatively low, but the generation of secondary microseisms in winter is likely higher, even for less intensive earthquakes from the group of catastrophic ones Holub et al 2013).…”

“…It has been shown that most microseisms anomalies are connected with atmospherics or strong earthquakes (Holub et al 2013). But, in fact, these influences were only triggers for the anomalous microseisms and not the reason of higher microseisms during winter.…”

“…The value of 3 was chosen according to the normal distribution of amplitudes around the average value at the 90% significance level (see for example Fig. 3b in Holub et al 2013). We obtained approximately 10% of the "anomalous" microseisms outside the median of the whole data set.…”

“…The most wellknown is the annual drift in microseisms amplitudes, which is explained by the annual drift of storms above the Atlantic and Pacific Ocean (Grob et al 2011). Holub et al (2013) showed in their paper that there are at least three other mechanisms, which can lead to secondary microseisms excitation. The first mechanism can be connected with the atmospheric pressure variations, the second is associated with the thermoelastic waves in the rock mass (Hvoždara and Brimich 1988;Brimich 2006), and the third one is associated with large earthquakes .…”

“…The maximal amplitude represents the annual variation in secondary microseisms, which were considered earlier as they are concerned with the annual trends in windstorms and cyclones (Zátopek 1964). Later Holub et al 2013 pointed out that similar lows and extensive windstorms above the Atlantic Ocean excited in the summer season did not trigger secondary microseisms with similar intensity as those in winter. This phenomenon can be explained by the fact that the storms are not the reason for microseisms excitation, but only the triggering mechanism, which depends on the stress background, which has an annual period (compare Figs.…”