Moho, seismogenesis, and rheology of the lithosphere
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- 作者：Wang-Ping Chen ; Chun-Quan Yu ; Tai-Lin Tseng ; Zhaohui Yang ; Chi-yuen Wang ; Jieyuan Ning ; Tiffany Leonard
- 关键词：Earthquake focal depths ; Mohorovi膷i膰 discontinuity ; Moho ; Mechanical instability ; Jelly sandwich model ; Caramel slab model
- 刊名：Tectonophysics
- 出版年：8 December, 2013
- 年：2013
- 卷：609
- 期：Complete
- 页码：491-503
- 全文大小：1397 K
文摘
The Moho is not always a sharp interface; but seismic phase SsPmp yields robust, physically averaged estimates of crustal thickness (virtual deep seismic sounding, VDSS). In S. Tibet where the Moho is as deep as 75 km, bimodal distribution of earthquake depths, with one peak in the upper crust and the other below the Moho, generated much interest in how lithological contrast affects seismicity and rheology. Generally seismicity is limited by distinct temperatures (Tc): 350 卤 50 掳C in the crust and 700 卤 100 掳C in the mantle (Earthquake Thermometry). Laboratory experiments show that distinct Tc reflect the onset of substantial crystal plasticity in major crustal and mantle minerals, respectively. Above these Tc, frictional instability ends due to velocity weakening of slip. So the seismic to aseismic transition is closely linked with brittle-ductile transitions in the crust and in the uppermost mantle, where the strength of the continental lithosphere is expected to peak (鈥淛elly Sandwich鈥?. Plasticity depends exponentially on temperature (which evolves over time), so interplay between the geotherm and crustal thickness could result in concentrated seismicity in the upper crust 鈥?the only portion of a very warm lithosphere where temperature is below ~ 350 掳C (鈥淐r猫me Br没l茅e鈥?. Conversely, where the entire crust is below ~ 350 掳C (and the uppermost mantle is also below ~ 700 掳C), then earthquakes could occur over a wide range of depths, including the entire crust and the uppermost mantle (鈥淐aramel Slab鈥?.