gravity field Andes 16 GOCE 12 Vertical gravity gradient 10 satellite data 10 earthquake rupture 8 Central Andes 6 Megathrust earthquakes 6 Nazca plate 6 continental margin 6 gravity anomaly 6 subduction zone 6 Bouguer anomaly 4 Chile 4 Earthquakes 4 Gravity gradients 4 Harmonic analysis 4 Patagonia 4 Rupture zone 4 Seismology 4 South America 4 Structural geology 4 Tectonics 4 Trench sediments 4 earthquake magnitude 4 lineament 4 lithospheric structure 4 magnetic field 4 satellite mission 4 slab 4