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Stories in the Shake: How to Decipher the Dramatic Changes Deep in the Earth Using Focus Mechanisms?
As the Earth continues to rotate, changes and activities deep underground affect the stability of the surface. The stories of shock may not be known, but they are slowly revealed through the analysis of the focus mechanism. The focal mechanism has not only become an important tool for scientists to understand the causes behind earthquakes, but also the key to studying the internal structure of the earth.
Basic concepts of focus mechanism
The focal mechanism describes the deformation that occurs in the source region of an earthquake and is closely related to the seismic waves that are generated. In fault-induced events, the focal mechanism shows the fault plane of slip and the slip vector. This explanation is also called the fault plane solution. By analyzing observed earthquake waveforms, scientists can infer focal mechanisms, a process that often relies on semi-automated analysis of waveform data.
Analysis of focal mechanisms not only reveals the origin of earthquakes, but also reflects the movement of the Earth's interior.
Momentum tensor solution of earthquake source
The momentum tensor solution for earthquakes is displayed in a graphical form known as a beach ball plot. When an earthquake produces a single direction of motion on a single fault plane, the pattern of energy radiated can be modeled as a double dipole. This modeling process is scientifically presented as a special second-order tensor.
Discovering the different radiation patterns of earthquakes and underground nuclear explosion exercises is crucial to preventing misjudgments and understanding the source of earthquakes.
Graphical Representation of a Beach Ball Chart
Seismic data are often rendered using the Lower Hemisphere Stereographic projection. According to the first movement direction of the P wave, different compression waves and tension waves can be distinguished. When there is enough observation data, two orthogonal great circles can be drawn, which divide the areas of compression and tension observation respectively, forming the so-called "node plane".
The determination of the nodal planes and their intersection point N (neutral axis) allows scientists to understand the characteristics of different faults.
Application of focus mechanism
The application of focal mechanism solutions is not limited to earthquake research, but also helps scientists explore the theory of seafloor spreading. By constructing focal plane solutions of seafloor faults, scientists discovered relative motion patterns of ocean deformation. The discovery helps show indirect evidence of ocean deformation and challenges previous classical geological interpretations.
Focal mechanisms provide us with powerful tools to gain insight into the structure and motion of the Earth's interior. These stories hidden deep underground give us a clearer understanding of the causes of earthquakes and help us predict possible geological activities in the future. In the face of the ever-changing Earth, can scientists further decode those stories that have yet to be revealed? Let us look forward to it together?
