Seismic Experiments on 3D Printed Earth Models

Abstract:

Understanding the seismic wave propagation in complex media—with small-scale heterogeneities, rough topography and interfaces, anisotropy, or pore fluids—is crucial to various aspects of geophysics such as earthquake ground motion prediction, induced seismicity, and energy exploration. Some of these problems are difficult to address using numerical approaches not only due to constraints in computing resources, but also due to inaccuracies in forward models and approximations that are being imposed. Alternatively, seismic experiments on physical models have been used in exploration geophysics, but these models are often limited to simplistic geometries or coarse structures.

In this work, we take advantage of 3D printing techniques to create physical models for seismic experiments. We mainly use metal as the 3D printing material since it can represent material properties as rigid as the Earth’s mantle at ambient conditions (~1 atm., ~25°C). By adjusting the printing parameters, i.e., the laser power and the scanning speed, during the printing process, we change the density structure within a printed model. This approach allows us to effectively represent a broad range of material properties, e.g., P-wave speeds of about 1-6 km/s. Based on the relationship between the printing parameters and seismic wave speeds, seismic velocity models with different levels of complexity are printed: a 3-layer model with topography, a basin model derived from the Southern­­ California velocity model (CVM-H model), and a multi-layer model with faults and tilted blocks (Marmousi model). We perform seismic experiments on the 3D printed models using laser doppler vibrometers and transducers as sources and receivers. The experiments result in record sections where a variety of seismic phases, e.g., direct and reflected body and surface waves, are identified. The measured travel times of major phases are consistent with predictions based on the input velocity models. Our study demonstrates 3D printing as a promising technique for constructing physical representations of Earth’s structure with high accuracy and realistic material properties. We believe seismic experiments on 3D printed Earth models provide unprecedented opportunities of understanding wave propagation problems.