Three-dimensional thermal modeling associated with subduction of the Cocos plate beneath southern Mexico, and its relationship to the occurrence of interplate seismic events

Abstract:

In the Pacific side of southern Mexico, the Cocos plate is subducting beneath the North American plate at the convergence rate of about 6.5 cm/yr. Megathrust earthquakes such as the 1985 Michoacan earthquake have occurred there repeatedly. The Guerrero seismic gap exists in the neighboring area, and a megathrust earthquake has been considered to occur there in the near future (Fig. 1). Besides, interplate seismic events such as slow slip events (SSEs) and non-volcanic tremor (NVT) are also identified in southern Mexico. In this region, so-called the “flat slab” exists whose northern rim is occupied bythe Trans-Mexican volcanic Belt (TMVB), which is a 1000 km long Neogene continental arc. Recent seismic surveys in Mexico elucidated seismic velocity structures along the profiles MASE and VEOX in detail, and these results enable us to estimate temperature fields in southern Mexico associated with subduction of the Cocos plate by numerical simulation. In this study, we constructed three-dimensional parallelepiped thermal convection model in southern Mexico to elucidate relationships among calculated thermal structures, above-mentioned interplate seismic events, and formation of the TMVB. We used heat flow data of observed Global Heat Flow Database (GHFD) and those estimated from Curie point depths to evaluate the validity of the calculated thermal structures. Our preliminary results show that low heat flow region above the flat slab appeared both in the observations and calculations as a common feature. In our presentation, we will demonstrate dehydration process associated with subduction of the Cocos plate by using phase diagrams of mid-ocean ridge basalt (MORB) and peridotite. Then, we will suggest relationship between the dehydration process and the occurrences of SSEs and NVT in southern Mexico.