#### Presentation Title

Inverting for Earth Structure Using Ocean Tides Loading the Surface

#### Presentation Type

Poster Presentation

#### Category

STEM (science, technology, engineering, mathematics)

#### Abstract/Artist Statement

The fundamental question of geophysics is simple: What is inside the Earth? Because we cannot physically travel there, we rely on indirect methods such as mapping the strength of Earth’s gravity or studying how fast earthquakes travel through Earth’s layers. Most of our knowledge of Earth structure comes measuring the two earthquake velocity, the pressure-wave velocity and shear-wave velocity. In order to turn these two velocities into material parameters such as density, shear modulus, and modulus, we need to make assumptions about Earth structure. These assumptions come in the form of scaling and combining the velocities to recover the elastic moduli. Not only does this step introduce uncertainty, but there is a fundamental flaw in using two parameters to calculate three: the three parameters are not independent of each other. In the crust and upper mantle, seismic methods cannot separate variations in density and elastic moduli. We need an independent method to separate the variations in Earth structure.

How Earth’s surface responds to a load is intrinsically a function of Earth’s structure. If we know the details of a loads and how much Earth’s surface moves in response to that load, we can solve for density, bulk modulus, and shear modulus. GNSS stations (the global terms for GPS stations) continuously measure the movement of Earth’s surface and have sub-millimeter accuracy. Ocean tides are extremely well studies and load Earth’s surface on the order of centimeters near shorelines and even move Earth’s surface as far inland as Missoula, MT. In our study, we use this ocean tidal loading to invert for Earth structure. We compare forward models of ocean tidal loading to GNSS measurements for the western United States and update a 2011 study.

#### Mentor Name

Hilary Martens

Inverting for Earth Structure Using Ocean Tides Loading the Surface

UC North Ballroom

The fundamental question of geophysics is simple: What is inside the Earth? Because we cannot physically travel there, we rely on indirect methods such as mapping the strength of Earth’s gravity or studying how fast earthquakes travel through Earth’s layers. Most of our knowledge of Earth structure comes measuring the two earthquake velocity, the pressure-wave velocity and shear-wave velocity. In order to turn these two velocities into material parameters such as density, shear modulus, and modulus, we need to make assumptions about Earth structure. These assumptions come in the form of scaling and combining the velocities to recover the elastic moduli. Not only does this step introduce uncertainty, but there is a fundamental flaw in using two parameters to calculate three: the three parameters are not independent of each other. In the crust and upper mantle, seismic methods cannot separate variations in density and elastic moduli. We need an independent method to separate the variations in Earth structure.

How Earth’s surface responds to a load is intrinsically a function of Earth’s structure. If we know the details of a loads and how much Earth’s surface moves in response to that load, we can solve for density, bulk modulus, and shear modulus. GNSS stations (the global terms for GPS stations) continuously measure the movement of Earth’s surface and have sub-millimeter accuracy. Ocean tides are extremely well studies and load Earth’s surface on the order of centimeters near shorelines and even move Earth’s surface as far inland as Missoula, MT. In our study, we use this ocean tidal loading to invert for Earth structure. We compare forward models of ocean tidal loading to GNSS measurements for the western United States and update a 2011 study.