Does an Anomalous Wave-form Signal can occur without Seismic Phase and Signifies Precursor of an Earthquake?

Review Article

Austin J Earth Sci. 2014;1(1): 6.

Does an Anomalous Wave-form Signal can occur without Seismic Phase and Signifies Precursor of an Earthquake?

Khan AA*

Department of Geology, University of Malaya, Malaysia

*Corresponding author: :Khan AA, Department of Geology, University of Malaya, Jalan Universiti, 50603 Kuala Lumpur, Malaysia

Received: March 03, 2014; Accepted: Aug 04, 2014; Published: Aug 06, 2014


Seismic waves precipitate in an earthquake is generated due to ‘physical jolt’/ ‘fault rupture ‘and propagate in an elastic-plastic domain through the earth crust. Seismic waves, thus generated, contain all the seismic phase viz., P-, S-, and Surface wave; and are recorded in broad-band seismographs. The seismic records/seismograms are used to determine location, magnitude and focal depth of an earthquake; and, focal mechanism solution of fault rupture. In contrast, when seismic wave does not contain seismic phase, they are referred to as noise or signal due to nuclear explosion. However, several anomalous signals without seismic phase have been observed before an earthquake those are distinctly different from noise and signal due to nuclear explosion. In this paper an occurrence of such anomalous signals prior to an earthquake are analyzed and correlated with the non-seismic signals and led to propose such anomalous signal a “pseudo seismic signal”. Further, such signals are suggested to occur due to micro-fracturing and its motion is linked to lattice dislocation movement process which can move earlier than brittle failure /fault rupture. Since lattice dislocation movement due to micro-fracturing is faster than the brittle failure that can move earlier than seismic wave. Large dislocation avalanche occur along a preferred slip plane. The dislocation movement of the micro-fracturing with no-slip boundary may emerge as an avenue for the movement of the pseudo seismic wave, a precursory signal of an earthquake.

Keywords: Anomalous signal; Micro-fracturing; Pseudo-seismic wave; Dislocation avalanche; Earthquake precursor


A variety of prediction methods have been used for centuries ranging from typical earthquake to observations of the arrangements of the planetary bodies and odd behavior of animals. The efforts include foreshock, anomalous seismic activity, seismic gap, b-value, source mechanism, hypo central migration of micro seismicity, changes in the ratio of seismic velocities, anomalous geomagnetic & geoelectric signals, and anomalous geochemical signals. Most have been unsuccessful due to its non-compliance with near real time attributes. No mechanism has yet been evolved for earthquake forecasting or alarm. However, the successful predictions have failed to provide any empirical relation applied to any precursory signals. Systematic efforts are being made to detect earthquake precursors since 1960s. Non-seismic signal such as geomagnetic signal, geoelectric signal, geochemical signal, electromagnetic signal, radon emission etc., are being tried as the precursors of an earthquake without much success. On the other hand, seismic signal generated by some ‘physical jolts’ like fault rupture are normally referred to as elastic wave or seismic wave. Non-seismic signals are also generated during the preparation phase of an earthquake. Some anomalous signals have been observed in the seismic records those are not typical non-seismic signal neither a seismic signal since they do not contain any seismic phase. A new acronym “Pseudo seismic” has been suggested for this anomalous signal. In this paper, an effort is given to correlate such signal with some theoretical bases and to understand the genesis of pseudo seismic signal. The paper deals with the problem pertaining to an earthquake that has occurred on July 27, 2003 in the Eastern Fold Belt of the Bengal Basin with a moment magnitude (Mw) 5.6 and focal depth 11 km (Figure 1). Seismogram of this earthquake revealed that five days prior to the main earthquake some anomalous signals were recorded those do not characterize signals due to an earthquake. Neither, there was any earthquake at the time of occurrence of the anomalous signal within thousand kilometers radius.