Earthquakes could possibly accelerate the rate of downslope movement of material in this case, but without knowing the rock type(s) involved, it would be difficult to assess the risk of complete and catastrophic failure.
IF the slope failed, simultaneously and completely, yes, water would be displaced and a displacement wave generated which could reach significant heights in the estuaries, threatening anyone living there and any vessels on the waterways.
But, since the situation has already been monitored for over 60 years, how soon that failure may occur, or whether the failure would continue as slow moving mass wasting remains to be seen. Considering the relative proximity to the 1964 earthquake epicenter, it is difficult to say with certainty that an earthquake would necessarily trigger a slope failure.