part of the premiums allocated to catastrophic coverage

i.e. ... the part of the business that had catastrophic effects...

se refiere al siniestro asegurado por la poliza. Depende del siniestro, seria damage, accident o loss.

Suggestions from "Word Magic"
seguro catastrófico - - «Seguros» (seguro con extensión de cobertura) catastrophic insurance
seguro con extensión de cobertura - - «Seguros» (seguro catastrófico) insurance with extended coverage , catastrophic
insurance

Wikipedia:
Extended coverage is a term used in the property insurance business. All insurance policies have exclusions - specific causes of loss (also called "perils") that are not covered by the insurance company. An Extended coverage endorsement(EC) was a common extension of property insurance beyond coverage for fire and lightning. Extended coverage added insurance against loss by the perils of windstorm, hail, explosion, civil commotion, riot and riot attending a strike, aircraft damage, vehicle damage, and smoke damage. The endorsement has been largely supplanted by what is referred to as "basic" causes-of-loss form first introduced by Insurance Services Office in 1986 as part of its simplified language revisions. The basic form includes most of the perils previously provided by fire and extended coverage and it adds vandalism and malicious mischief, sprinkler leakage damage, sinkhole collapse, and volcanic action.