Assessment of Seismic Fault Rupture, Ground Deformation and Subsidence Hazards
for the Ford-Otosan Automobile Assembly Plant in Kocaeli, Turkey
The August 17, 1999 earthquake in Turkey caused:
- Surface fault rupture along the southern perimeter of the Ford-Otosan Turkish Automobile Assembly Plant;
- Significant damage to Ford-Otosan’s new buildings, especially to the body shop, where the columns were tilted;
- Regional subsidence of as much as 1.5 meters where the main plant buildings are located;
- Synclinal warping and secondary faulting associated with a step in the main fault, at the Golçuk stepover; and
- Lateral slumping and spreading of sediments into the Marmara Sea to the north of the property.
Earth Consultants International was asked to evaluate the probability of another similar earthquake occurring during the lifetime of the plant. Paleoseismic trenching confirmed the historic record of large earthquakes, separated in time by about 200 years. This evidence was critical to assessing short and moderate term risk. It was determined that the Ford-Otosan plant has a low probability of experiencing a similar earthquake in the next 50 to 100 years. However, it will likely experience smaller earthquakes (aftershocks) generated by the same fault system, and lower, attenuated ground motions as a result of earthquakes on other faults some distance from the site. Based on these results Ford-Otosan decided to rebuild the plant rather than moving their facility elsewhere.
Fault Hazard Assessment Study
for the Proposed La Jovita LNG Terminal Site
Baja California, Mexico
Tectonic Geomorphic Reconnaissance
of the Pedro Miguel, Azota, Miraflores, and other faults
Panamá Canal Area and Vicinity, Panamá
Following up on our successful paleoseismic studies of the Gatún and Limón faults, the Autoridad del Canal de Panamá (ACP) authorized Earth Consultants International to investigate the entire Panamá Canal area for the presence of other active faults. The intent of the study was to identify other potential seismic hazards within the Canal watershed that should be included into the seismic hazard model being developed for the Canal Expansion project. Because of the large area to be studied, a heavy reliance was placed on aerial imagery mapping, terrain model analysis, helicopter reconnaissance, and tectonic geomorphic mapping. These techniques were supplemented with a targeted field reconnaissance program at sites identified as likely to provide positive or negative evidence for recency of activity on the faults being studied.
The tectonic geomorphic mapping indicated a high probability that the Azota and Pedro Miguel faults are active seismic sources. Both faults sharply deform all streams where they cross the fault indicating they are both right-lateral strike-slip faults, similar to the Limón fault studied earlier. A previously unmapped fault along the east side of Lake Madden also shows clear evidence for recurrent Holocene activity. The mapping also indicated a lower risk of seismic activity on the Miraflores and Caballo faults. In addition to the faults, we also estimated an uplift rate for the Caribbean Coast of Panamá and evaluated the possibility that the Gatún fault continues farther west across Gatún Lake. All results were presented to ACP management and their Geotechnical and Seismic Advisory Boards.
Paleoseismic Investigations of the Pedro Miguel Fault for Design of the Panamá Canal Expansion Project
As part of the design studies for the Panamá Canal Expansion Project, the Autoridad del Canal de Panamá (ACP) authorized Earth Consultants International (ECI) to undertake a quantitative paleoseismic investigation to determine the slip rate, recurrence intervals, recency, magnitude, location, and rupture kinematics of the Pedro Miguel fault. The fault was initially identified as a potentially active fault by ECI in a regional tectonic geomorphic mapping project as part of studies into the seismic hazard to the existing Canal. Because of the Pedro Miguel fault’s proximity to the existing Miraflores and Pedro Miguel locks, and its location through the Expansion Project’s Borinqu&enacute; Dam, the fault would pose a significant design constraint for the project.
The investigation began with detailed research of the existing geologic investigations for the original Panamá Canal, the design studies for the 1939-41 Third Locks Project, and the new Canal Expansion Project. The trenching phase of the study was conducted over two phases, eventually totaling over 75 trenches and exposures. The study successfully located the fault through the entire Expansion Project area, resolved a right-lateral slip rate of 3.6 to 8.0 mm/yr, and determined that the fault has ruptured three times in the past 1,600 years. The study also successfully resolved slip per event, recency of activity, and recurrence intervals at three different sites along the fault. In a follow-up study, we also confirmed that the last rupture of the Pedro Miguel fault resulted in a 2.8 to 3.0 meter displacement that occurred on May 2, 1621 and severely damaged the original capital of Panamá Viejo. The results of our work were presented to the ACP’s Geotechnical, Seismic, Structural, and Paleoseismic Advisory Boards, ACP’s upper management, and political leaders.
Peer Review Panel for Landslide Mitigation at the Ocean Trails Golf Course
Rancho Palos Verdes, California
The Ocean Trails Golf Course, located on an elevated marine terrace at the tip of the Palos Verdes Peninsula, has had a history of adverse landslide impacts even before it was opened. Three coastal landslides (A, B, & C) had been mapped within the course’s footprint during design studies. In 1998, landslide C dramatically reactivated, taking Holes 10 & 11 into the sea. The failure was repaired, and the course rebuilt. However, the failure led to a renewed scrutiny of the current stability of landslides A & B, and their future stability after new additions to the project were completed, including the Clubhouse expansion, a driving range, and a dozen new homes above landslide A. Over the course of 3+ years, the developer’s geotechnical team and the City of Rancho Palos Verdes’ geotechnical reviewers were consistently unable to reach concurrence on the geological model that would ultimately underpin the stability analysis and any required mitigation efforts. Principals from three firms: Earth Consultants International, GeoKinetics, and AMEC, were retained jointly by the developer and the city to serve as a Peer Review Panel between the two conflicting geotechnical firms, and attempt to bring their opinions together and allow the project to move forward.
The Peer Review Panel reviewed the extensive geotechnical documentation that had been created over 20 years of studying the site. The Panel conducted its own field reconnaissance and mapping, including rappelling down the sea cliff to map, measure, and sample the exposed strata. Four additional borings were drilled and cored at key locations where the two interpretations differed to bring hard data to bear on differentiating between them. These borings were installed with groundwater monitoring piezometers and slope movement inclinometers for future monitoring. After all the existing and new data were reviewed and analyzed, the Panel prepared a review report and held several meetings with the two parties to share the results and help them to understand the differences. The work of the Panel ultimately had two cycles, very similar in scope, as both parties continued to disagree, and more work was done on both sides, including more drilling. Although eventually neither side was pleased, portions of the project were allowed to move forward, albeit with a different design.