Ipak Fault System Monitor

We present the up-to-date seismicity associated with the Ipak fault system as a series of space-time sections. The aim is to reveal the hidden orders and to facilitate prompt interpretation. The earthquake data is obtained from the IRSC and the ISC databases every minute. With new earthquakes the figures and maps are updated immediately; otherwise, they are regenerated every hour. The following points should be considered regarding the images.

  1. There are 8 figures showing time-space sections of seismicity for different periods. Earthquakes are projected on the line segments that represent the Ipak fault system.
  2. The yellow line segments, ‘E-W’, on the maps show the section. Earthquakes within a 20 km range are projected in the section.
  3. For each figure X, there are 3 associated illustrations with a corresponding period. Xa shows the seismicity for the whole region, while Xb displays the events in the window around the section. Figure Xc shows the depth distribution of events along the section. Their links are given below each figure.
  4. The thick red line segments that are labeled L, M, and N on the maps and also along the right axis of each figure represent seismic gaps.
  5. The thick magenta line segments along the left axis or within the figures, (5-100 km, 150-250 km, and 250-281 km), in turn, show the partial projection of the macroseismic area of the 23 February 0958 (M~7.7), the surface rupture of 01 September 1962 (M~7.0) (Ambraseys and Melville, 2005) and the surface rupture of the 22 June 2002 (Mw 6.5) earthquakes (Mahdavifar et al., 2006).
  6. Segments L and M are separated due to the uncertainty on the existence of a strike-slip fault along L, which coincides with the presumably North Rey fault. Nazari et al. (2010) questioned such a fault segment; therefore, it is essential to analyze the mechanism of any microseisms, with depths more than 5 km, within a narrow band around L. A left-lateral strike-slip mechanism would be conclusive on the continuation of the Ipak fault in Tehran area.
  7. Any other reverse fault segment within the Tehran area, e.g. the Milad Tower fault, is unlikely to be linked with the continuation of the left-lateral Ipak fault.
  8. The L segment is limited in the east by crossing the NE-trending Parchin fault.
  9. Provided that L represents a left-lateral fault segment, it is likely that both segments M and L rupture in a single earthquake with a length of about 95 km. This is about the same length that ruptured during the 1962 Ipak earthquake.
  10. The pale-green polygon shows the extents of Tehran.
  11. The earthquake data for the post-2006 period is obtained from the IRSC catalog, while the ISC database is the data source for earlier times.
Elements and details that may become unrecognizable due to dense seismicity or background color of the maps.
Click to open map 1a, map 1b or figure 1c
Click to open map 2a, map 2b or figure 2c
Click to open map 3a, map 3b or figure 3c
Click to open map 4a, map 4b or figure 4c
Click to open map 5a, map 5b or figure 5c
Click to open map 6a, map 6b or figure 6c
Click to open map 7a, map 7b or figure 7c
Click to open map 8a, map 8b or figure 8c

Acknowledgment

The earthquake data for this project is obtained from (i) the “Iranian Seismological Center” (IRSC) of the Institute of Geophysics, University of  Tehran and (ii) the International Seismological Center (ISC). We appreciate these institutions for the release of their products to the public. The figures are produced by using the “Generic Mapping Tool” (GMT) and we thank the developers of the software (Wessel et al., 2013).

References

  • Ambraseys NN, Melville CP. A History of Persian Earthquakes. Cambridge university press; 2005.
  • Mahdavifar MR, Solaymani S, Jafari MK. Landslides triggered by the Avaj, Iran earthquake of June 22, 2002. Engineering geology. 2006;86:166–182.
  • Nazari H, Ritz J-F, Salamati R, et al. Distinguishing between fault scarps and shorelines: the question of the nature of the Kahrizak, North Rey and South Rey features in the Tehran plain (Iran). Terra Nova. 2010;22:227–237.
  • Wessel P, Smith WH, Scharroo R, Luis J, Wobbe F. Generic mapping tools: improved version released. Eos, Transactions American Geophysical Union. 2013;94:409–410.