Investigation of strong ground rotation attenuation in Los Angeles area

Recently, the instrument technology (e.g., ring laser) is capable to accurately record the ground rotational motions induced by earthquakes. However, due to the scarcity of data, the systematic ground rotation variation is still a challenge. In order to answer that question, we simulate several M7 earthquakes with different source scenarios on the Newport-Inglewood (NI) fault embedded in the Los Angeles basin and investigate the corresponding propagation properties. At first, complex ground rotation variations are observed with respect to the source scenario (i.e., varying hypocentre location and varying slip history). With the decrease of the fault distance, the amplitude of both the acceleration and the rotation rate stop to increase. For the two components of acceleration and rotation rate, there are obviously high values in some fault distance range where a sedimentary basin is located (basin amplification effect). Finally, by comparing the acceleration and rotation rate at different fault distance, we conclude that the rotation rate follows the same rule to attenuate with the fault distance, except for the very small fault distance range. The peak amplitude of the vertical rotation rate changes more dramatically with the fault distance than the the other two components.