Explaining seismic activity in Asia Pacific region
Updated
Natural disasters have hit the region this week - with floods in Southeast Asia, as well as earthquakes and tsunamis in the South Pacific. While the tremors may not be directly linked, they are part of a flurry of seismic activity on the so-called "Ring of Fire" and have tested the region's tsunami warning systems.
Presenter: Sen Lam
Speaker: Phil Cummins, senior seismologist at research organisation Geoscience Australia
- Listen:
- Windows Media
CUMMINS: They are connected in the broad sense that they have both occurred at the edges of the Australian Plate. They are also connected in the sense that they've hit communities that perhaps could have been better prepared for them, but other than I don't think there is a causal connection between the two of them.
LAM: And, of course, some people have pointed out that there has been a jump in seismic activity in the Indonesian fault since the 2004 tsunami, and certainly over the past few weeks, there has been considerable activity around the Australian Plate, in Java and even in parts of southeastern Australia. What's behind this flurry of seismic activity?
CUMMINS: Oh, I think there are a couple of things behind that. I think the earthquakes in Sumatra and possibly even in Java - there is a stronger argument that they could be connected, because they are of reasonable close proximity to each other and the stress changes that occur after major earthquake can in fact affect areas around the epicentral region. So I think there is an argument that both quakes in Sumatra and possibly in Java have some connection. I think it is much more difficult to argue that there is a causal connection between say southeast Australian earthquakes, Indonesian earthquakes and south west Pacific earthquakes, because of the distances are much larger. Having said that, it is possible for seismic waves to cause triggering of earthquakes over great distances, that has been seen for smaller cluster earthquakes and that possibility cannot be completely discounted, but it's extremely difficult to prove that that has actually happened here.
LAM: Phil Cummins, the Indonesian archipelago lies within the infamous 'Ring of Fire' - but has seismic activity been more frequent over the past few decades or have they just been better recorded due to new technology?
CUMMINS: Well, I think the occurrence of large earthquakes since the 2004 event is certainly an increase in seismicity and there is as I said, there could well be linkages, especially between earthquakes that are occurring on the same fault, such as the ones off Sumatra, that have occurred on the Sumatran mega-thrust that separates the two plates, the Australian Plate ducking under the Sunda block there and now the recording of smaller earthquakes may have been increased by instrumentation, but these large earthquakes have been picked up by. You don't need a lot of instrumentation to pick up these large earthquakes and there is no question that their frequency has increased since the 2004 event.
LAM: And of course, following the tsunami in late 2004, there was much talk about early warning systems. How are the current systems working and indeed if there is increased seismic activity, should we be concerned? How prepared are we?
CUMMINS: Well, I think there has been a vast improvement in warning systems in the Indian Ocean and in the Pacific since the 2004 event. But by and large, these warning systems are mainly effective for regional and distant tsunamis that you really need a fair bit of lead time in order to detect and characterise an earthquake, but especially to get the message out to communities, get the warning out to the people who actually need it. For the disasters we have seen recently and particularly the one in Samoa, as well as the earlier tsunami disasters in Sumatra, those are local tsunamis which arise can arise with 20 or 30 minutes from the earthquakes occurrence and that's much more difficult to warn for. I think it is difficult to argue that the current systems are effective for that and that they. I think it is difficult to argue that any technological system is more effective than the one that is in place now, educating people and getting them to go, to seek higher ground as soon as they feel strong shaking.
