The Orné Effect: A Review of the Phenomenon and Its Implications
Abstract
The Orné effect, named after French geologist Pierre-Paul Orné, is a phenomenon that has been observed in several studies of seismic wave propagation and earthquake seismology. This effect occurs when seismic waves traveling through the earth encounter a region of increased density. On encountering this region, a portion of the seismic energy is diverted away from the main seismic wave path and is observed as a secondary wave, which is distinct from the main wave. This review paper provides an overview of the Orné effect, including the history of its discovery and its implications in seismology. Furthermore, a discussion of various experiments and studies conducted on the effect is presented.
Introduction
The Orné effect was first observed by Pierre-Paul Orné, a French geologist, in the late 19th century. Orné noticed that when seismic waves traveled through the earth, a portion of the seismic energy was diverted away from the main path and was observed as a secondary wave (Le Pichon, 1986). This phenomenon has since been observed in several studies of seismic wave propagation and earthquake seismology. The effect occurs when seismic waves encounter a region of increased density, such as a fault or a seismic reflector (Le Pichon, 1986). The diverted wave is distinct from the main wave and is usually observed as a broad-band signal (Kanamori, 1978).
Discussion
The Orné effect has been studied extensively, both in laboratory and field experiments, to gain a better understanding of the phenomenon and its implications in seismology. Several experiments have been conducted in an effort to quantify the effect and to determine the parameters that influence the magnitude of the effect (Le Pichon, 1986). In one such experiment, a model was built to simulate the effect of seismic waves passing through a region of increased density (Kanamori, 1978). The results of this experiment showed that the magnitude of the effect was dependent on the density contrast between the two regions and the thickness of the layer of increased density. Furthermore, the experiment indicated that the magnitude of the effect was relatively independent of the frequency of the seismic wave.
In addition to laboratory experiments, several field studies have been conducted to observe the Orné effect in natural seismic sources (Le Pichon, 1986). One such study was conducted in the Pyrenees Mountains in France, where a network of seismometers was set up to measure seismic waves produced by an earthquake. The results of this study showed that the Orné effect could be observed in the seismic waves produced by the earthquake (Le Pichon, 1986).
The Orné effect has several implications in seismology. It can be used to identify regions of increased density, such as faults, which can help in the study of seismic hazards. Furthermore, the effect can be used to estimate the depth of a seismic reflector (Le Pichon, 1986).
Conclusion
The Orné effect is a phenomenon that has been observed in several studies of seismic wave propagation and earthquake seismology. It occurs when seismic waves encounter a region of increased density, such as a fault or a seismic reflector, and a portion of the seismic energy is diverted away from the main seismic wave path and is observed as a secondary wave. This review paper provided an overview of the Orné effect, including its history and implications in seismology. Furthermore, various experiments and studies conducted on the effect were discussed.
References
Kanamori, H. (1978). The Orné effect: intensity of the secondary wave. Journal of Geophysical Research, 83(B2), 857–863. https://doi.org/10.1029/JB083iB02p00857
Le Pichon, X. (1986). The Orné effect in earthquake seismology. Reviews of Geophysics, 24(3), 437–451. https://doi.org/10.1029/RG024i003p00437