Two-Dimensional Attenuation and Velocity Tomography of Iran

Abstract

Seismic bulletin data collected by the Iranian Seismological Center are used to image crust and mantle seismic attenuation, group velocity, and phase velocities for Lg, Pg, Sn, and Pn phases. This is possible because the peak amplitude time is picked, and amplitude measurements can be associated with the phase based on travel time plots. The group velocity is the apparent velocity of the maximum amplitude arrival and represents the combined effect of phase velocity and seismic scattering. Thus, it can be used in combination with the attenuation to identify where scattering attenuation is dominant. The Arabian–Iranian plate boundary separates low-velocity Zagros sediments from central Iran; however, in the mantle, it separates a high-velocity Arabian shield from central Iran. Scattering attenuation is low within the Arabian mantle and crust, and the Zagros sediments do not cause Lg or Pg attenuation. The Eocene Urumieh Dokhtar Magmatic Arc has high attenuation within both the crust and mantle, and while there is no partial melting in the crust, there may be some in the mantle. The northern Eocene Sistan Suture Zone shows particularly high attenuation that is accompanied by high scattering. It represents an incompletely closed ocean basin that has undergone intense alteration. The Alborz Mountains have high attenuation with some scattering.

Crustal Lg Attenuation Beneath the Iranian Plateau: Implications for Cenozoic Magmatism Related to Slab Subduction, Slab Break‐Off, and Mantle Flow

“…Crustal P‐ and S‐wave attenuation imaging results also show strong attenuation throughout the whole Iranian Plateau, but more details are difficult to decipher (Pasyanos et al., 2021). Recently, Hearn (2022) conducted seismic attenuation tomography for Lg, Pg, Sn, and Pn phases in the Iranian Plateau. Both in the crust and uppermost mantle, the Iranian Plateau shows strong attenuation characteristics compared with the surrounding regions, and prominent low‐$${Q}_{\mathrm{Lg}}$$ anomalies are revealed beneath the UDMA, Lut Block, Kopet‐Dogh Mountains and Alborz and Talesh Mountains (Hearn, 2022).…”

“…Inside the Iranian Plateau, low‐velocity anomalies were mainly revealed beneath the Lut Block and Kopet‐Dogh Mountains in the east and the Alborz and Talesh Mountains in the west (Pei et al., 2011), which was consistent with the Lg‐wave attenuation observations. The Arabian Plate underlying the Zagros orogen and the subducting Makran subduction slab both exhibited high velocities in the uppermost mantle, which were distinguished from crustal attenuation features (e.g., Amini et al., 2012; Hearn, 2022; Lü et al., 2017; Pei et al., 2011).…”

“…Seismic velocity tomography in the uppermost mantle was widely performed in and around the Iranian Plateau (e.g., Al‐Lazki et al., 2004, 2014; Alinaghi et al., 2007; Amini et al., 2012; Hearn, 2022; Hearn & Ni, 1994; Lü et al., 2012, 2017; Mahmoodabadi et al., 2019; Pei et al., 2011). As shown in Figures 7c–7d, overall low Pn and Sn velocities were revealed in the Anatolian, Iranian, and Pamir Plateaus and Afghan Blocks (Pei et al., 2011), which corresponded well with the strong attenuation in the crust.…”

“…As shown in Figures 7c–7d, overall low Pn and Sn velocities were revealed in the Anatolian, Iranian, and Pamir Plateaus and Afghan Blocks (Pei et al., 2011), which corresponded well with the strong attenuation in the crust. The Eurasia region north of the Iranian Plateau showed high Pn and Sn velocities (e.g., Amini et al., 2012; Hearn, 2022; Lü et al., 2017; Pei et al., 2011). Inside the Iranian Plateau, low‐velocity anomalies were mainly revealed beneath the Lut Block and Kopet‐Dogh Mountains in the east and the Alborz and Talesh Mountains in the west (Pei et al., 2011), which was consistent with the Lg‐wave attenuation observations.…”

“…Several previous studies have conducted Lg attenuation tomography in and around the Iranian Plateau (Al‐Damegh et al., 2004; Cong & Mitchell, 1998; Hearn, 2022; Kaviani et al., 2015; Pasyanos et al., 2009; Sandvol et al., 2001; Zhao & Xie, 2016). The Lg‐coda $${Q}_{0}$$ at 1.0 Hz ranges between 150 and 300 across the Turkish and Iranian Plateaus, and the $${Q}_{0}$$ across the Arabian Shield and platform is approximately 300–450 (Cong & Mitchell, 1998).…”