Earthquake Report: Iran

A couple weeks following the earthquake in eastern Iraq, there was a sequence of earthquakes in central eastern Iran. These earthquakes are too distant to be related. The Iranian sequence includes a M 6.1 foreshock on 2017.12.01 and two M 6.0 aftershocks on 2017.12.12. Here is my report for the M 7.3 earthquake.

While putting together my annual summary for 2017, I wanted to include a poster that shows these two earthquakes as they relate to regional historic seismicity (with fault plane solutions).

https://earthquake.usgs.gov/earthquakes/eventpage/us1000bjnz/executive#executive

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1917-2017 with magnitudes M > 6.5.

I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 6.1 earthquake. I also include USGS fault plane solutions for most of the earthquakes in the region.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. Based upon the tectonics associated with the San Andreas and Maacama faults, I interpret this M 4.3 earthquake to be a right-lateral strike-slip fault.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include MMI contours for most of the earthquakes that have fault plane solutions plottted.

    • I include some inset figures.

    • In the upper right comer is a map from Peretti et al. (2011) that shows the plate boundaries in this region. I place blue stars in the general location of the M 7.3 and M 6.1 earthquakes. The M 6.1 earthquake happened in a region of north striking strike slip faults.
    • In the lower left corner is a map from Javadi et al. (2013) which shows the tectonic domains for this region. I place two blue stars in the general location of the M 7.3 and M 6.1 earthquakes. The M 6.1 earthquake sequence appears related to the Kubanan or Naiband faults.


    • Here is my poster for the M 7.3 earthquake. See the Earthquake Report page for more information about the tectonics in the region.


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    • Here is the tectonic map from Peretti et al. (2011).


      • Tectonic sketch map of the Persian Gulf and Arabian Peninsula, modified from Al-Husseini (2000), Ziegler (2001) and Pollastro (2003).

    • Here is the map from Javadi et al. (2013).


      • (Colour online) (a) Tectonic setting of Iran in the Middle East and presentation of major convergence vectors of the region. (b) Main sedimentary-structural zones of Iran (modified from Aghanabati, 2004). Major faults discussed in the text are shown. White and black arrows from Sella, Dixon & Mao (2002) and Vernant et al. (2004), respectively. DFS – Doruneh Fault System, MRZF – Main Zagros Reverse Fault, HZF – High Zagros Fault, MFF – Mountain Frontal Fault, ZFF – Zagros Foredeep Fault.

    • Here is a great fault map from Walker and Jackson (2004). The M 6.1 earthquake sewuence was located in the region of Fig. 8 a (shown below as a Landsat map).


      • GTOPO30 image of central and eastern Iran showing the major fault zones and geographical regions. Black and gray arrows represent Arabia-Eurasia plate motions. Rates are in millimeters per year. Black arrows are GPS estimates from Sella et al. [2002] and gray arrows represent 3 Ma magnetic anomaly plate motions which are a combination of the Africa-Eurasia plate motion from Chu and Gordon [1998] and the Africa-Arabia plate motion of DeMets et al. [1994] (see Jackson et al. [1995] for method). Arabia-Eurasia convergence occurs in the Zagros, the Alborz, and Kopeh Dagh, and possibly in central Iran by the rotation of strike-slip faults (see later discussion). Right-lateral shear between central Iran and Afghanistan is taken up on N–S right-lateral faults of the Gowk-Nayband and Sistan suture zone systems, which surround the Dasht-e-Lut. North of 34N, the right-lateral shear is taken up on left-lateral faults that rotate clockwise.

    • Here is a map showing the location of the Gowk fault, also with the geomorphology (shown on the LANDSAT map) associated with this fault system. This is the map labeled as Fig 8.


      • (a) GTOPO30 topography of the Kerman region centered on the Gowk fault (see Figure 1 for location). Fault plane solutions of shallow (<35 km) earthquakes are shown. Black solutions are events modeled using body waveforms (listed by Jackson [2001], Walker [2003], and Talebian and Jackson [2004]); dark gray represents events from the Harvard CMT catalogue with >70% double-couple component; light gray represents first-motion solutions [from McKenzie, 1972]. Zones of shortening and thrust faulting are seen both to the north of Kerman, where the Gowk fault splits into the Kuh-Banan, Lakar-Kuh, and Nayband faults, and south of Mahan, where NW–SE trending thrust faults occupy the region between the Sabzevaran and Gowk faults. These zones of intense deformation may be partly caused by rotation of crustal blocks, as marked by black arrows (see section 5.3). The box marks the location of Figure 8b. (b) Landsat TM image of the central part of the Gowk fault. Restoration of drainage and structural features indicate between 12 and 15 km of cumulative right-lateral displacement [Walker and Jackson, 2002]. Restoration of 15 km of right-lateral slip aligns dark-colored lithologies (marked X), although it is not certain that the dark-colored rocks at either side of the fault are from a single displaced unit.

    • Here is the aerial image map of this region (Walker and Jackson, 2002). The M 6.1 sequence occurred to the northeast of Fandogo.


      • LANDSAT TM image and location map of the Gowk fault region.

    • This figure shows the Walker and Jackson (2002) interpretation for the structures in the region of the Gowk fault. The M 6.1 earthquake is most likely related to the Shahad thrust fault system (also noted on the above map).


    • This is a plot from the International Seismological Center (ISC) that shows seismicity in plan view (the map) and cross sectional view.


      • Historical seismicity map based in ISC Bulletin data for yesterdays Mw 7.3 on Iran-Iraq border. Mostly shallow thrust events in a complex tectonic setting.

    • UPDATE: After chatting with Dr. Eric Fielding on twitter, I discovered a paper that he wrote discussing the faults in the region of the M 6.1 sequence. Perfect! They relate fault growth in a fold and thrust belt (Shahad thrust faults) to aseismic slip, based upon modeling (constrained by InSAR data) of the 1998.03.14 Fandoqa M 6.6 earthquake. However, given the M 6.1 sequence, we now know that all the growth is probably not aseismic.


      • A: Shaded relief topographic map of Shahdad area with active faults (medium black lines) (Walker and Jackson, 2002), XX9 profile location (thick black line), moderate earthquakes (black filled circles), four large earthquakes since 1981 (white filled circles), and fault-plane solution (upper right) for Fandoqa earthquake (Berberian et al., 2001). Rectangles with thin black lines are Fandoqa rupture (F) and Shahdad basalthrust (S) dislocations shown in other figures. Thick dashed white line—Gowk fault zone; P—central Iranian plateau; L—Lut block. B: Topographic profile and depth cross section of Fandoqa main shock, Shahdad basal thrust, and splay slip planes. Solid lines show positions of fault planes from inversion after adjustment for topography; dashed lines are unadjusted. Gray fill shows Shahdad thrust wedge.


      A: Average of two interferograms, converted to radar range change (motion in radar line of sight) in millimeters. Faults (black lines) and profile location (white line) as in Figure 1A. Rectangles (thin lines) show surface locations of Fandoqa and Shahdad basalthrust dislocation models. B: Surface deformation from Fandoqa main-shock elastic model, shown as radar range change. Large rectangle outlines area shown in C and D. C: Residual interferogram after subtracting Fandoqa main shock model shown in B. Note that color scale and area are different from A and B. Green labels are Universal Transverse Mercator zone 40 coordinates and tics are every 10 km. Thin red lines show updip projections of Fandoqa and Shahdad basal thrust to surface. Larger rectangle shows extended Shahdad basal thrust used in distributed slip inversion (Fig. 3) and Poly3D (Fig. 4). D: Surface deformation predicted by slip model of Shahdad basal thrust and splays shown in Figure 4, projected into radar line of sight. Same area and colors as C.

Here are the USGS pages for the main earthquake in this sequence.

    References

  • Allen, M.B., Saville, C., Blac, E.K-P., Talebian, M., and Nissen, E., 2013. Orogenic plateau growth: Expansion of the Turkish-Iranian Plateau across the Zagros fold-and-thrust belt in Tectonics, v. 32, p. 171-190, doi:10.1002/tect.20025
  • Fielding, E.J., Wright, T.J., Muller, J., Parsons, B.E., and Walker, R., 2004. Aseismic deformation of a fold-and-thrust belt imaged by synthetic aperture radar interferometry near Shahdad, southeast Iran in Geology, v. 32, no. 7, p. 577-580, doi: 10.1130/G20452.1
  • Giardini, D., Grunthal, G., Shedlock, K., Zhang. P., and Global Seismic Hazards Program, 1999. Global seismic hazards map: Accessed on Jan. 9, 2007 at http://www.seismo.ethz.ch/GSHAP.
  • Javadi, H. R., M. Esterabi Ashtiani, B. Guest, A. Yassaghi, M. R. Ghassemi, M. Shahpasandzadeh, and A. Naeimi (2015), Tectonic reversal of the western Doruneh Fault System: Implications for Central Asian tectonics, Tectonics, 34, 2034–2051, doi:10.1002/ 2015TC003931.
  • Jenkins, Jennifer, Turner, Bethan, Turner, Rebecca, Hayes, G.P., Sinclair, Alison, Davies, Sian, Parker, A.L., Dart, R.L., Tarr, A.C., Villaseñor, Antonio, and Benz, H.M., compilers, 2013. Seismicity of the Earth 1900–2010 Middle East and vicinity (ver 1.1, Jan. 28, 2014): U.S. Geological Survey Open-File Report 2010–1083-K, scale 1:7,000,000, https://pubs.usgs.gov/of/2010/1083/k/.
  • Perotti, C.R., S. Carruba, M. Rinaldi, G. Bertozzi, L. Feltre and M. Rahimi, 2011. The Qatar–South Fars Arch Development (Arabian Platform, Persian Gulf): Insights from Seismic Interpretation and Analogue Modelling in Earth and Planetary Sciences » Geology and Geophysics » “New Frontiers in Tectonic Research – At the Midst of Plate Convergence”, book edited by Uri Schattner, ISBN 978-953-307-594
  • Stern, R.J. and Johnson, P., 2010. Continental lithosphere of the Arabian Plate: A geologic, petrologic, and geophysical synthesis in Earth-Science Reviews, v. 101, p. 29-67.
  • Taymaz, T., Yilmaz, Y., and Dilek, Y., 2007. The geodynamics of the Aegean and Anatolia: introduction in Geological Society, London, Special Publications, v. 291; p. 1-16, doi:10.1144/SP291.1
  • Verges, J., Saura, E., Casciello, E., Fernandez, M., Villasenor, A., Jimenez-Munt, I., and Garcia-Castellanos, D., 2011. Crustal-scale cross-sections across the NW Zagros belt: implications for the Arabian margin reconstruction in Geol. Mag., v. 148, no. 5-6, p. 739-761
  • Walker, R. and Jackson, J., 2002. Offset and evolution of the Gowk fault, S.E. Iran: a major Intra-continental Strike-Slip System in Journal of Structural Geology, v. 24, p. 1677-1698.
  • Walker, R. and Jackson, J., 2004. Active tectonics and late Cenozoic strain distribution in central and eastern Iran in Tectonics, v. 23, doi:10.1029/2003TC001529
  • Woudloper, 2009. Tectonic map of southern Europe and the Middle East, showing tectonic structures of the western Alpide mountain belt.

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