I found a reference - he (kerry seih) says:
The record at Pallett Creek5, 16, 29 shows that rupture has recurred about every 130 years, on average, over the past 1500 years. But actual intervals have varied greatly, from less than 50 years to more than 300. The physical cause of such irregular recurrence remains unknown.

Kerry Seih's web page is linked below

There's a link on the Earthwave's Bookstore page to his recent book - The Earth in Turmoil: Earthquakes and Volcanos and Their Human Impact - Its very good reading - great for the layperson or professional.

Canie

• Kerry Sieh