In order to image the Earth's elastic properties and/or to understand the physics of earthquakes, we need to be capable of simulating seismic wave propagation for a given medium or a given scenario of earthquake rupture and nucleation process. When we would like to image the Earth's interior or earthquake dynamics, we need first to forward model seismic wave propagation. When the model is very close to the reality, one might want to continue further on, by inverting the observed data. Here in IPGP, theoretical and numerical seismology groups are looking for accurate and efficient way of seismic wave propagation simulation as well as source dynamics of earthquakes.
Depending on what we want to see and on how much big the dataset to be analysed, we balance accuracy and efficiency of methodology. For instance, in order to image the Earth's global structure (down to the centre of the inner core: 6371 km deep!) or the subsurface structure (to look for gas and oil reservoirs: ~1-2 km deep), seismologists have used ray theory very often, which is an infinitely high-frequency assumption of wave propataion, or then novel asymptotic theory to high frequency or long-wave surface wave calculation. However, the Fresnel zone of seismic waves is rather volumetric and thus it is very important to take into account its effect when we analyse waveforms. Seismology Laboratory in IPGP is pushing the frontiers to acquire more accurate and efficient methodologies in order that we are able to calculate high-frequency body-wave waveforms accurately even for an entire Earth model.