This excerpt taken from the SIRI 10-Q filed Nov 12, 2008.
XMs service network or other ground facilities could be damaged by natural catastrophes.
Since XMs ground-based network is attached to towers, buildings and other structures around the country, an earthquake, tornado, flood or other catastrophic event anywhere in the United States could damage its network, interrupt its service and harm its business in the affected area. XM has backup central production and broadcast facilities; however, it does not have replacement or redundant facilities that can be used to assume the functions of XMs repeater network in the event of a catastrophic event. Any damage to XMs repeater network would likely result in degradation of XMs service for some subscribers and could result in the complete loss of service in affected areas. Damage to XMs central production and broadcast facility would restrict its production of programming to its backup facilities.