Study of the earthquake source process and seismic hazards

Thesis

To obtain the rupture history of the Parkfield, California, earthquake, we perform 12 kinematic inversions using elliptical sub-faults. The preferred model has a seismic moment of 1.21 x 10¹⁸ Nm, distributed on two distinct ellipses. The average rupture speed is ~2.7 km/s. The good spatial agreement with previous large earthquakes and aftershocks in the region, suggests the presence of permanent asperities that break during large earthquakes.

We investigate our inversion method with several tests. We demonstrate its capability to retrieve the rupture process. We show that the convergence of the inversion is controlled by the space-time location of the rupture front. Additional inversions show that our procedure is not highly influenced by high-frequency signal, while we observe high sensitivity to the waveforms duration.

After considering kinematic inversion, we present a full dynamic inversion for the Parkfield earthquake using elliptical sub-faults. The best fitting model has a seismic moment of 1.18 x 10¹⁸ Nm, distributed on one ellipse. The rupture speed is ~2.8 km/s. Inside the parameter-space, the models are distributed according the rupture speed and final seismic moment, defining a optimal region where models fit correctly the data. Furthermore, to make the preferred kinematic model both dynamically correct while fitting the data, we show it is necessary to connect the two ellipses. This is done by adopting a new approach that uses b-spline curves. Finally, we relocate earthquakes in the vicinity of the Darfield, New-Zealand earthquake. 40 years prior to the earthquake, where there is the possibility of earthquake migration towards its epicentral region. Once it triggers the 2010-2011 earthquake sequence, we observe earthquakes migrating inside regions of stress increase. We also observe a stress increase on a large seismic gap of the Alpine Fault, as well as on some portions of the Canterbury Plains that remain today seismically quiet.

Authors: Twardzik, C

• Publication date: 2014
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: seismic hazards; synthetic tests; kinematic inversion; dynamic inversion; stress transfer; earthquake relocation
• Subjects: Earthquakes and tectonics; Seismology