6. Conclusion

The Vancouver area has been expecting a large seismic event to occur for a period of hundreds of years.  This is referred to as the return period of an earthquake.  In general there is a logarithmic linear relationship between the intensity of an earthquake and the return period.  The last record of a major earthquake was approximately 400 – 500 years ago.  This means that the upcoming earthquake is expected to be fairly large, considering the size of the seismic gap.  Therefore the Vancouver area has high potential for sustaining structural and non-structural damage, associated with monetary losses and many severity levels of injuries and casualties.  By modeling the results for MMI VI-XII, we have produced predicted values for the outcomes of the various earthquake events.

When examining the outcomes for direct monetary losses, the results are highly dependent on the building prototype and associated replacement cost.  The top 10 buildings were all constructed out of concrete materials, which have relatively high replacement cost values.  Out of all the concrete prototypes, it appears that building size is the next most determinant factor, with CFHR as the most prominent prototype in the top 10.  In fact, 70% of the top 100 buildings are of this prototype because concrete is so widely used in the construction of large buildings in Southwestern British Columbia.  Therefore large concrete buildings will result in elevated monetary losses due to their massive size and expensive replacement cost.  However, this was not necessarily the most expensive prototype when comparing moderately sized buildings (2,000 – 2,400 sq/ft of total area). An interesting comparison of building prototypes for moderate sized buildings is shown in Table 6.0.1.  This comparison shows the RCFIW as the most expensive prototype in terms of direct monetary losses.  This prototype is expected to sustain extensive structural damage, and reinforced concrete materials cost $25 more per square foot to replace compared to concrete.  When looking at these moderately sized buildings, it appears that CFLR is the worst type of concrete building.  This prototype is worse than CFHR due to the high non-structural MDF values.  For example, in an MMI X event, the CFLR prototype has an MDF value of 9.5% for acceleration sensitive non-structural damage, whereas CFHR has a value of 1.8%.  Also at the same intensity, CFHR has an MDF value of 15.9% for displacement sensitive non-structural damage compared to 26.9% for CFLR.  Therefore CFLR appears to perform worse than the CFMR and CFHR prototypes for buildings of equal size; however due to the fact that it is a low rise prototype, the maximum potential for direct monetary loss will be significantly lower due to the constraints on total area.

Table 6.0.1. Direct Monetary Loss Comparison of Prototypes for Moderate Sized Buildings

The second highest monetary loss value was the WPB prototype due to the relatively high non-structural MDF’s and a substantial structural MDF value.  For an MMI X event, WPB has MDF values of 14.3% for acceleration sensitive, and 28.6% for displacement sensitive components.  WPB also costs more than concrete materials to replace.  With a structural MDF of 31.6%, WPB can expect to sustain higher monetary loss values then most other prototypes in the study area.  Fortunately this prototype is only found in 48 buildings, representing 0.5% of all buildings in our study area.  This prototype is also of great concern due to its potential for direct social loss.  The following table reveals that casualties may occur within a WPB building with 424 people, in an MMI IX or greater event (Table 6.0.2.).  In this example, only un-reinforced masonry prototypes and WPB show casualties in an MMI X event.  Therefore, the WPB prototype is expected to sustain elevated amounts of direct monetary loss, which is also accompanied with heavy direct social loss, causing increased risk in a seismic event.

Table 6.0.2. Direct Social Loss Comparison of Prototypes for Moderately Populated Buildings

In this example, the SFMI and RCFIW prototypes reveal the highest risk for slight and serious injuries.  These prototypes are expected to have injuries beginning at MMI VIII, which increase significantly with each seismic intensity.  These two prototypes contain masonry infill walls, making them poorly designed for seismic forces, resulting in extensive damage and partial collapse.  The top 7 prototypes in this example (highlighted in grey) are all constructed with masonry as part of its structural components.  When comparing moderately populated buildings (between 412 – 450 people), these prototypes produce the highest numbers of injuries and casualties across the study area.  Therefore any building containing a significant portion of masonry is at high risk in any seismic event, due to masonry’s potential for extensive damage and social loss.

The resulting direct social losses are dependent upon the population of a given building.  The population of a building was determined for three separate time scenarios, which was related to a specific building occupancy type.  Occupancy type was fundamental because it determined when large amounts of people were in each building, depending on the scenario.  Occupancy type was an essential factor in deriving time scenario building populations from Canadian census variables.    This impacted the results by allocating an accurate number of injuries and casualties into a specific space and time.  For example, a residential building would allocate the most severe results to the 2 a.m. time scenario, due to the increased number of occupants.  In fact for an MMI X event, 89% of all social loss at 2 a.m. occurs in residential and hotel buildings, whereas at 2 p.m., 75% occur in commercial and educational buildings.

The results showed an alarming number of injuries and casualties in educational buildings.  In total, educational buildings contain 49 fatalities, 27 life threatening injuries, 169 serious injuries and 543 slight injuries in an MMI X event occurring at 2 p.m.  However, the most alarming result was the block containing the Vancouver General Hospital, which is expected to sustain the highest values of direct monetary and social losses for every seismic scenario.  For an MMI X event occurring at 2 p.m., this block contains a total of 18 fatalities, 10 life threatening injuries, 86 serious injuries and 267 slight injuries.  This block will also sustain $4,147,740 of direct monetary losses.  These statistics are disturbing because many young children appear to be at high risk, and the Vancouver General Hospital also appears to have high risk which could disrupt the function of vital emergency services.  These results therefore show that these educational and hospital buildings need to be upgraded due to the level of seismic risk in Southwestern British Columbia in order to reduce the level of social vulnerability.