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Crustal velocity structure in Borneo Island using receiver function inversion

Syuhada Syuhada, Pranata Bayu, Anggono Titi, Ramdhan Mohamad, Zulfakriza Zulfakriza, Febriani Febty, Prasetio Aditya D., Dewi Cinantya N., Hasib Mohammad, Sulaiman Albertus

Acta Geophysica

2022

Vol. 70, no 6

2529--2553

Borneo is an island situated in a tectonically complex region and characterised by multiple arcs and continental blocks accreted during the Mesozoic and early Cenozoic. We analyse receiver functions of teleseismic events from 12 seismic stations around the island. In general, these stations sample a variety of geological environments, including Meratus Complex, Eastern Borneo, South–Western Borneo, North–Western Borneo, and Sabah Zones. We then derive the shear wave velocity models from the inversion of receiver functions using the stochastic non-linear approach. Inversion results indicate that the island is covered by sedimentary layers with thickness ranging from 1 to 3 km thick. The inversion solutions for most stations also show that the crustal thickness varies between 26 and 36 km around the region. The variation in the average crustal Vp/Vs values obtained for each seismic station addresses the geological diversity of the study area. Furthermore, the lowvelocity zone with high and low Vp/Vs in the lower crust observed beneath some seismic stations may be associated with the tectonic evolution and development of Borneo Island. The results inferred from our inversion are generally consistent with other previous geological and geophysical studies conducted in this region.

Nonlinear robust output feedback control of submersibles via modeling error compensation

Nambisan P. R., Singh S. N.

Systems Science

2007

Vol. 33, no 4

27-35

This paper treats the design of a nonlinear robust dive-plane control system for multivariable submersibles equipped with bow and stern hydroplanes. It is assumed that the vehicle's parameters and the hydrodynamic coefficients are not known, and that disturbance forces due to the sea wave are acting on the vehicle. For the design, the depth and pitch angle are chosen as output variables. Using nonlinear input-output (pitch angle and depth) map inversion, a robust nonlinear output feedback control law for the trajectory control of the pitch angle and depth id derived. For synthesizing the robust inverse control law, the unknown functions and unmeasurable variables are estimated using a high-gain observer. It is shown that in the closed-loop system, the asymptotic tracking of the depth and pitch angle trajectories is accomplished. Simulation results are presented which show precise dive-plane maneuvers in spite of uncertainty in the system parameters and disturbance forces due to the sea waves.

Application of nonlinear methods to inversion of 1D magnetotelluric sounding data based on very fast simulated annealing

Miecznik J., Wojdyła M., Danek T.

Acta Geophysica Polonica

2003

Vol. 51, nr 3

307-322

The inversion of geophysical data depends on the availability of a priori information on the geology of the earth inversion method chosen, and the appropriate definition of parameters of the model. Traditionally, 1D magnetotelluric data have been inverted by the trial-and-error method, which employs iterated, linearized inversion methods. However, this approach involves a good knowledge of parameters of the analyzed earth. Unlike the linearized inversion, the nonlinear inversion does not depend so much on a starting model; however, a proper choice of the starting model can reduce the time and cost of computation. In this paper the authors applied a nonlinear optimization method, called very fast simulated annealing (VFSA), to one-dimensional inversion of magnetotelluric sounding data. The authors made some simplified assumption concerning the selection of cooling constants and reducing the equivalence of geoelectric models. The inversion was performed in three ways: the individual inversion of amplitude data, individual inversion of phase data, and joint inversion of amplitude and phase data.