16:15 〜 16:30
[SIT19-10] 波形インバージョンによる南大西洋下D″領域の3次元S波速度構造推定
キーワード：最下部マントル、波形インバージョン、アフリカLLSVP、D″領域
The D″ region is the thermal boundary layer at the lowermost several hundred kilometers of the mantle and plays an essential role in mantle dynamics. In the D″, two large low shear velocity provinces (LLSVPs) are known to exist: one beneath the Pacific and another beneath Africa. Areas of low-shear wave velocity suggest heterogeneity in temperature, chemical composition, or both put together, but the exact cause of this velocity decrease is not yet understood. Mantle circulation simulations have found that if mantle convection is driven solely by the effect of temperature, gatherings of small thermal plumes called “plume clusters” will be created, while large masses of chemical heterogeneity referred to as “thermochemical piles” will be formed if chemical heterogeneity plays a role in driving the circulation. Many previous studies have carried out whole-mantle inversions and envisaged the seismic structure of the lowermost mantle, but their horizontal resolution of around 1000 km is insufficient to distinguish between thermochemical piles and plume clusters.
In this study, we utilize a large amount of data from seismic arrays in Africa that has recently become available, as well as those from surrounding regions, and conduct waveform inversion for 3D S-wave velocity structure of the western boundary region of the African LLSVP. A total of ~3600 transverse-component broadband body-wave seismograms obtained from the IRIS datacenter are used. They include data of seismic waves from deep- and intermediate-focus earthquakes recorded at epicentral distances of 70-100 degrees. A large amount of data enables us to achieve a resolution of ~250 km horizontally and ~50 km vertically, allowing insights into the internal structure of the African LLSVP.
In the presentation, we will show the inferred 3D S-wave velocity structure of our target region along with resolution checks conducted to validate those results and discuss whether the African LLSVP is closer to the picture of thermochemical piles or to that of plume clusters.
In this study, we utilize a large amount of data from seismic arrays in Africa that has recently become available, as well as those from surrounding regions, and conduct waveform inversion for 3D S-wave velocity structure of the western boundary region of the African LLSVP. A total of ~3600 transverse-component broadband body-wave seismograms obtained from the IRIS datacenter are used. They include data of seismic waves from deep- and intermediate-focus earthquakes recorded at epicentral distances of 70-100 degrees. A large amount of data enables us to achieve a resolution of ~250 km horizontally and ~50 km vertically, allowing insights into the internal structure of the African LLSVP.
In the presentation, we will show the inferred 3D S-wave velocity structure of our target region along with resolution checks conducted to validate those results and discuss whether the African LLSVP is closer to the picture of thermochemical piles or to that of plume clusters.