Earthquake Tectonics and Prediction Research
 

 

 

Earthquakes are the result of ruptures of the rocks under tectonic stress. Therefore, they are a physical process that should in principle be predictable. However, only few earthquakes have been successfully predicted and there is no known method that works in general. To understand tectonic processes to a point that earthquakes can in some cases be predicted, or at least partially predicted, should be a principal goal of seismologists, but many capable scientists keep clear of the subject because amateurs and idealists who do shoddy science meddle in the topic of earthquake prediction research. WAPMERR takes the attitude that tectonic processes should be studied in a rigorous manner with the aim to possibly one day predict some earthquakes.

Seismicity patterns is a research topic in which WAPMERR personnel have collaborated with researchers at the Federal Institute of Technology in Zuerich, Switzerland, the National Meteorological Office in Reykjavik, Iceland and the University of Paris. We study two different parameters: (1) The ratio of the number of small to large earthquakes (the b-value in the equation log N = a ⍩, and (2) seismicity rate changes.

(1) b-value Patterns

Our research group has developed strong evidence that b-values are inversely proportional to stress and that asperities are in some places mapped by low b-value. Asperities are the crustal volumes from where a maximum of seismic energy is radiated during an earthquake and from where the rupture often initiates. These are the highly stressed volumes along a fault zone and the recurrence time in them is the lowest. Therefore, it is important to identify asperities.

The results of these studies are reported in the following papers.

Schorlemmer, D., S. Wiemer, and M. Wyss (2004), Earthquake statistics at Parkfield I: Stationarity of b-values, J. Geophys. Res., 109, B123234, 123210.121029/122004JB003234.

Schorlemmer, D., S. Wiemer, and M. Wyss (2005), Variations in earthquake-size distribution across different stress regimes, Nature, 437, 539-542.

Wyss, M. (2001), Locked and creeping patches along the Hayward fault, California, Geophys. Res. Lett., 28, 3537-3540.

Wyss, M., and S. Matsumura (2002), Most likely locations of large earthquakes in the Kanto and Tokai areas, Japan, estimated based on local recurrence time, Phys. Planet. Int., 131, 173-184.

Wyss, M., and S. Matsumura (2005), Verification of our previous definition of preferred earthquake nucleation areas in Kanto-Tokai, Japan, Tectonophys., 417, 81-84.

Wyss, M., C. Sammis, R. Nadeau, and S. Wiemer (2004), Comparison between seismicity on creeping and locked patches of the San Andreas fault near Parkfield, California: fractal dimension and b-value, Bull. Seism. Soc. Am., 94, 410-424.

Wyss, M., and R. Stefansson (2006), Nucleation points of recent main shocks in southern Iceland mapped by b-values, Bull. Seism. Soc. Am., 96, 599-608.

As an example we tested the hypothesis that most larger than average earthquakes should occur in the volumes of shortest recurrence times (low b-values) Figure 1 shows that epicenter of earthquakes during the 4.5 years after we had published a map of asperities in the central part of Japan mostly do fall into these locations proposed as asperities

Epicenters (cirlcles) of the earthquakes with M > 3.8 between 1999.0 and 2003.5 in the declustered catalog.  The study area selected in our previous work (Wyss and Matsumura, 2002) is outlined by a dashed line, the previously mapped areas of anomalously low recurrence time are outlined by sold lines and colored pink.  Of the 23 events 19, or 83%, fall into the anomalous areas.

   
 
 
  We also map the tectonic fabric, by the heterogeneity of seismic behavior to help understand where earthquakes are most likely to happen. As an example Figure 2 shows a three dimensional map of the ratio of small to medium sized earthquakes (b-value) in southern Iceland. In this area, this parameter varies strongly over distances of only 1 km. As in others areas WAPMERR investigated, main earthquake ruptures emanate from the volumes with the largest percentage of medium sized earthquakes (darkest blue in the figure).    
 

(2) Seismic Quiescence

   
 

 

WAPMERR has also participated in developing evidence supporting the hypothesis of seismic quiescence as a possible precursor. “Seismic quiescence” is defined as a statistically significant seismicity rate decrease that occurs before a major earthquake in and around its source volume and that cannot be explained by artificially introduced reporting changes.

In one case study the hypothesis of precursory seismic quiescence was confirmed by WAPMERR research. Figure 3 shows that in a large part of normally active Sakhalin Island not a single earthquake occurred during 2.5 years before the M7.6 Neftegorsk earthquake of 26 May 1995 that killed about 2000 people. The map at the left shows the center of the region of statistically most significant quiescence in red.

Reference: Wyss, M., G. Sobolev, and J. D. Clippard (2004), Seismic quiescence precursors to two M7 earthquakes on Sakhalin Island, measured by two methods, Earth Planets and Space, 56, 725-740.