Damaging Aftershocks in Northern Italy: Cumulative Insured Losses €300 to €700 Million
Two damaging aftershock earthquakes, a M5.8 followed by a M5.4, occurred Tuesday, May 29, in Italy's Emilia-Romagna region, which experienced a M6 mainshock on May 20. In light of these events, EQECAT's revised estimate of insured loss from the May 20 event and its aftershocks is €300 to €700 million ($375 to $875 million USD). This loss estimate is particularly sensitive to uncertainty in estimates of exposed values and insurance penetration rates.
The aftershocks affected a similar area to the mainshock. They occurred within 15 km of the epicentre of the M6.0 event on May 20, about 30 km northwest of the city of Bologna. Like the mainshock, aftershocks have occurred at shallow depths of 10 km or less. The affected area and distribution of shaking is also similar to that of the May 20 event, with a maximum intensity level VII on the Modified Mercalli MMI scale in the localized epicentral region.
Shakemap M5.8 Aftershock - May 29, 2012
Source: U.S. Geological Society (USGS)
Extensive building damage and several fatalities have been reported. Affected structures include residential buildings, churches, and commercial buildings. Workers throughout the region were evacuated, and several thousand people are now reported to be displaced from their homes since the May 20 event.
Many of the structures that experienced significant aftershock damage likely experienced damage from the initial earthquake. In some cases, pre-existing damage might not have yet been apparent. No major infrastructure damage has been reported.
Estimation of Insured Loss
The current insured loss estimate of €300 to €700 million is a significant upward revision from EQECAT's original estimate of €100 million with a credible upper bound of €200 million. Reasons for the increase include the contribution to losses from the most recent aftershocks and updated insight on insured values in the region.
Scores of smaller aftershocks have occurred in the region. These latest events are expected to create significant new losses. Despite the lower magnitude of the events on May 29, these aftershocks could significantly contribute to insured losses, given the increased vulnerabilities of structures already affected by the May 20 event. Furthermore, the region remains at risk of additional damaging aftershocks.
Overall insured losses are also sensitive to the value of commercial facilities and their contents (notably food and industrial production in the region) for which insurance penetration and cover is highly variable.
EQECAT's insured loss estimate is based on assumed insurance penetration rates of approximately 3% to 5% for commercial/industrial lines of business and 1% or less for residential. With low take-up rates and relatively small area of strong shaking, industry loss estimates are particularly sensitive to geographic distribution of exposure covered by insurance. Damage to a single facility could significantly influence total industry losses, if that facility happens to be one of the covered minority.
This exposure uncertainty is the primary reason for the breadth of the range in EQECAT's insured loss estimate.
The May 29 events impacted a similar area to the event of May 20. The towns of Mirandola, Finale Emilia, San Felice, Cavezzo and San Possidonia were significantly impacted. Affected buildings further afield, including in the city of Bologna, are being investigated for structural integrity.
Affected buildings were those shaken by the initial event and comprise primarily historic buildings of unreinforced brick masonry, as well as more modern precast concrete structures.
The Po river plain has experienced relatively few historical earthquakes, and consequently this area has been classified as a region of low- to moderate-seismicity. The last earthquake exceeding M5 in the immediate vicinity of the recent events occurred in 1570. Accordingly, mapped seismic hazard used in building codes for the region have required a relatively low level of earthquake-resistant design.
A typical construction method for precast concrete frame structures is for columns and beams to be pre-fabricated at a concrete plant, delivered to site, and lifted into place. It is common for beam-column connections to consist of simple bearing ledges.
Source: The Applied Technology Council, with modifications by EQECAT
In this configuration, when the building experiences horizontal motion, the beam can slide off its support, causing collapse. In addition, typical wall construction for the region includes the use of unreinforced hollow clay tile units. Although this construction material is common in regions of low- to moderate-seismicity, it is a well-documented earthquake vulnerability.
EQECAT Event IDs
Users of EQECAT's WORLDCATenterprise™ are advised to consider event ID 18011 as the best-matched proxy for this earthquake. Event IDs 21772 and 14508 can be used to evaluate magnitude sensitivity, and event IDs 17961, 18012, and 18060 can be used to evaluate location sensitivity.
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