Lower crustal seismic activity in the Adana Basin (Eastern Mediterranean): Possible connection to gravitational flexure

• Published in: Tectonophysics 2018-04, Vol.730, p.1-10
• Main Authors: Ergin, Mehmet, Aktar, Mustafa
• Format: Article
• Language: English
• Subjects: Adana Basin; Basins; Broadband; Continental dynamics; Deep crustal seismicity; Double difference location; Duration; Earthquakes; Eastern Mediterranean; Evolution; Flexing; Flexure; Gravity; Mathematical models; Modelling; Parameters; Relocation; Seismic activity; Seismicity; Seismology; Subsidence; Thermal properties; Thermodynamic properties
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2018.02.015

High quality broadband data, together with the application of the double difference relocation technique, has been used to study the characteristics of the lower crustal seismicity in the Adana Basin, in southwestern Turkey. Deep events are clearly seen to be restricted only to the Adana Basin and never extend outside its boundaries. Furthermore, the seismogenic zone is observed to align roughly with the main axis of the basin and plunges steadily in the SSW-direction, following the basement trend of the Adana Basin. Similarities between geometries of the basin evolution and the deep seismic production suggest that both processes are closely related. A flexure process is proposed related to the subsidence of the Adana Basin. The seismogenic zone, originally at a shallow depth, is assumed to have been displaced vertically into the lower crust, by flexure. The temperature evolution of the crust during the flexure has been studied in detail using finite difference modeling, with amplitude and duration parameters taken from earlier studies. It has been concluded that the physical conditions for brittle fracturing remained unchanged for an extended period of time after the flexure. The brittle layers originally at shallow depths, preserved their original thermal properties after the subsidence and will continue to produce earthquakes at considerable depths. Numerical tests using inferred parameters imply a total vertical shift of 7–8 km for the seismogenic zone. Discussions for additional processes, which may further contribute to the cooling of the crust, are also included. •Accurate location of deep events in Adana Basin (Eastern Mediterranean) by dense networks and double difference relocation.•Similarity of basin geometry and deep seismicity suggests gravitational flexure driving the seismogenic zone downwards.•Thermal modeling of lithospheric flexure by finite difference and the subsequent deepening of the seismic cutoff boundary.•Implification for an average vertical shift of 7-8 km for the seismogenic zone.