In response to the March 11th 9.0 magnitude earthquake and subsequent tsunami, researchers from Oregon State University, the University of Hawaii Manoa, and engineers from Martin and Chock in Hawaii received a NSF Rapid (# 1138699) grant to conduct TLS surveys of selected regions damaged during the event. The scan team was in the field from June 24 through July 3rd, 2011 collecting data from the greater Sendai region, Onagawa, Minamisanriku, and Rikuzentakata. The reconnaissance efforts were greatly facilitated by our Japanese collaborators from Saitama University and the Building Research Institute (BRI) in Tsukuba.
The research field team consisted of a mixture of structural engineers, geomatics graduate students, and tsunami experts. The focus of the reconnaissance effort was to gather and digitally preserve as much structural and topographic data as possible to facilitate modeling tsunami impact forces and effects on structures. The delay from event to survey combined with the occurrence of a tsunami meant that most evidence of earthquake damage was eradicated. As a result, the majority of data collection focused on steel frame and reinforced concrete buildings. The majority of these exhibited varying degrees of deformation or failure due to the tsunami event. Where possible, the team captured examples of surviving structures for comparative analysis. As discussed in recent articles on lidarmag.com and Engineering News-Record, Asia Air Survey also collected mobile scan data throughout this region.
Although there were a great many affected areas, time constraints and logistics forced us to narrow our efforts to a select few cities which exhibited useful research examples. The reconnaissance team returned from Japan with approximately 100 gigabytes of data. Around 90% of this consisted of laser scan data with digital photographs comprising the remainder. The TLS data was collected from 103 scan positions allowing us to acquire an estimated 4 billion points. Laser scan data were collected for the most important sites, while secondary sites were documented with photographs and manual measurements. GPS was used to collect approximate global locations for each scan. These data will be analyzed in order to characterize the post impact conditions encountered throughout the region. Types of analyses may include the deformations to structures and infrastructure, displacement or destruction from pre-existing states, and quantification of scour damage.
While preliminary analyses of the data have been undertaken, it will take time to fully compile and analyze the extensive volume of data collected during this reconnaissance. The combination of structural and topographic elements will hopefully provide an enhanced view of the forces which the town was subjected to during the tsunamis duration. The goal of studying disasters such as the Tohoku earthquake and tsunami, as well as other world events, is to continually evaluate and improve construction codes and practices so that the severity of events to come might be lessened. LiDAR technology has proven invaluable for completing such studies by digitally preserving the scene so that engineers and scientists can virtually visit the location to validate models and theories.