Generating Digital Earthquake-Triggered Ground Failure Inventories for Historical Earthquakes

Abstract:

Earthquake-triggered ground failure, such as landslides and liquefaction, can be a major contributor to the total losses from an earthquake. Hazard models for predicting ground failure in earthquake-prone regions are improved by calibrating against high-quality ground-truth field observations, which in recent years, are compiled in ground failure inventories. Ground failure observations gathered after earthquakes in the past few decades have become more accurate and detailed with the advance of technology such as GPS and remote sensing, but observations of earthquake-triggered ground failure have been documented for many decades, particularly for major, consequential events. Data from these large historic events are very valuable in simulating effects of potential analogous modern-day events. In this study, we develop two ground failure inventories by compiling and digitizing historical documents containing ground failure data from two major earthquakes, the 1906 San Francisco earthquake and the 1964 Great Alaska earthquake. The 1906 San Francisco earthquake ruptured a long stretch of the San Andreas fault and triggered a remarkably high number of well-documented landslides over a widespread area. The 1964 Alaska earthquake had an unusually long duration of shaking, generating extensive deep and shallow landsliding. There are complications to digitizing the ground failure data for these earthquakes, including large location uncertainty, such as references to landmarks no longer present, and inconsistency in data quality, such as having detailed maps of some features and vague descriptions of others. Historical topographic maps and local historical records were very useful in confronting these challenges, and attribute fields were added to delineate different kinds of data and accuracy. Ground failure inventories for these two earthquakes consolidate observations that were previously not available digitally and were spread over many publications. These digital inventories contribute to an existing USGS-hosted ground failure inventory database that can be used to improve the ground failure models necessary for accurate real-time hazard and impact calculations, as well as for scenario exercises and long-term mitigation planning.