Elmer has an education in applied geophysics, but he drifted towards the field of seismology when he started to apply seismic interferometry and reflection imaging to naturally induced wavefields.

Naturally induced seismic wavefields are mainly caused by earthquakes and microseism sources. The first is generally known, the second source is a coupling of ocean-wave interaction with the solid earth. When naturally induced wavefields are measured at the Earth's surface, they contain many complicated reverberations from structure below the seismic sensor. With seismic interferometry in combination with reflection imaging, these multiple reverberations are used to make an image of this structure. Applications on different scales and to different wavefields can be found under 'Publications'.

Human activity in the subsurface, like pumping water in an aquifer, or hydrocarbon extraction, can be a cause of stress build-up along a fault: e.g., a differential pressure may develop between a reservoir compartment being partly emptied of gas, and a neighboring compartment that keeps fully pressurized. The stress can be released by a (sudden) slide along the fault: an earthquake. For mitigating this human induced seismicity, it is of paramount importance to understand where the seismicity is occurring. Using the first arriving waves at the Earth's surface yields a limited sensitivity in depth. To better focus the location of the seismic sources, Elmer investigates the use of multiple reverberations from structure near the source.