These are in contrast to low-frequency volcanic earthquakes which have a very different character and may be indicators of a possible eruption. Swarms of these types of events are fairly common on many volcanoes. Even smaller earthquakes can sometimes be detected and located though some also are missed.Īll of the earthquakes in the Mount Hood sequences have characteristic waveforms similar to tectonic earthquakes.
There are a good number of seismograph stations located on (2) or very near (5) the volcano such that the regional seismic network can reliably detect and locate earthquakes of magnitude 0.5 and larger in this area. See the blog for more details.īelow you will find an epicenter map, time-depth plot and seismicity plot for a region around Mount Hood for the three decades, 1980 - 2010 that shows typical or background levels of earthquakes in this region. NOTE: A depth of 0.0 (zero) km is at sea level and thus events within the volcano will plot above sea level (negative depths). We think these changes are very small but one should still be aware of this possibility. Keep in mind that the PNSN earthquake recording and processing system changed in very major ways starting in 2012 and thus there can be small biases or changes introduced in event detection, location and size. unless, of course unusual activity takes place that suggests a different time sequence is needed to better interpret that activity. This plot is updated weekly until 2020 when a new plot will start. More extensive explainations of Mount Hood swarms is contained in a blog posting about a swarm in 2019 and more recently and slightly to the east a swarm in January 2021.īelow is a time-depth plot of earthquakes located directly under Mount Hood since 2010. 2012 a very small earthquake swarm took place resulting in a blog posting on the PNSN web pages. The largest event in the roughly 15 sequences during the 1990s varied from M=1.6 to M=3.5. The largest event in a swarm usually does not occur at the beginning (such as a main shock-after shock sequence). These swarms usually last from a few hours to a couple of days and have had as many as 50 well located earthquakes and as few as 4. Over three quarters of the earthquakes that were located at Mount Hood during the 1990s occurred in these types of swarms. Seismicity at Mount Hood is primarily characterized by fairly intense swarms of micro-earthquakes which typically occur about 4 to 7 km south of the summit.
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