Emmy-Noether-Project "Bridging Geodesy and Seismology"

Joint use of near-field and far-field data

To characterise earthquake sources to with more robustness and to more detail we aim to use more measurements in our inferences than the standard approaches.



Earthquakes are caused by shear-failures of rocks that have been strained beyond their strength by external forces, e.g. from tectonic forces. During the failures hazardous seismic waves are exciting and the rock around the rupture gets deformed.


 

If the earthquake is large enough (magnitude 5.8 and larger) and the source shallow and on-land we can measure and analyse the caused surface displacement as well as the seismic waveforms, which for these earthquake sizes travel and can be recorded globally.



Surface displacements are caused by shallow crustal earthquakes of magnitude 6 and larger because they deform the rock around them considerably. For magnitude 6 earthquakes rock displacement reaches several decimeters up to meters close to the rupture (only a few kilometers away) and slowly decreasing displacements for tens of kilometers away from the rupture.

With this information we can locate an earthquake source very precisely. Larger earthquakes with larger rupture planes and larger slip on the fault cause larger displacements and larger deformed areas.

With this information we can determine the rupture size and magnitude. Also the pattern of the surface displacement is characteristic for certain properties of the rupture, e.g. large vertical surface displacements for ruptures with vertical fault slip and large horizontal surface displacements for ruptures with horizontal fault slip.

With this information we can estimate the mechanism of the earthquake.


How we globally measure surface displacements from space [link zu Seite]


Seismic waveforms carry information on the rupture time and the rupture duration. The amplitude of the seismic waves increases with earthquake magnitude, but also depend on the positions between the earthquake source and the recording station.

The reason is that seismic waves are radiated in a so-called radiation pattern, which is determined by the orientation of the rupture plane and the rupture mechanism, so that the waveform pattern and the amplitudes change depending on the azimuth and the distance of the recording station to the earthquake source.

Using the seismic wave travel times we can also locate distant earthquakes.


How we globally measure seismic waveforms [link zu neuer Seite
 

Geofon

SRCMOD Database