{"id":10493,"date":"2022-11-11T20:52:19","date_gmt":"2022-11-11T20:52:19","guid":{"rendered":"https:\/\/earthjay.com\/?p=10493"},"modified":"2023-01-01T00:11:27","modified_gmt":"2023-01-01T00:11:27","slug":"earthquake-report-m-7-3-tonga-trench-outer-rise","status":"publish","type":"post","link":"https:\/\/earthjay.com\/?p=10493","title":{"rendered":"Earthquake Report: M 7.3 Tonga trench outer rise"},"content":{"rendered":"

Early this morning I received some notifications of earthquakes along the Tonga trench (southwestern central Pacific Ocean). It was about 2am my local time. <\/p>\n

I work on the tsunami program for the California state tsunami program (CTP) and we respond to tsunami to (1) help local communities do their first response activities so that they can help reduce suffering and to (2) document the impact of these tsunami.<\/p>\n

Because of this work, our team is “at the ready” 24 hours a day, 7 days a week, to respond to these events. Luckily, this event was unlikely to generate a tsunami that would impact California. I went back to sleep.<\/p>\n

This morning I put together a report and checked to see if there was a tsunami generated. Here is one place that I check for tsunami records as observed on tide gages http:\/\/www.ioc-sealevelmonitoring.org\/map.php<\/a>. I did not see anything convincing.<\/p>\n

This earthquake, from last night my time, has a magnitude of M 7.3.<\/p>\n

https:\/\/earthquake.usgs.gov\/earthquakes\/eventpage\/us7000ip0l\/executive<\/a><\/p>\n

This area of the Earth has a plate boundary fault system called a subduction zone. A subduction zone is a convergent plate boundary, which means that the plates on either side of the boundary move towards each other.<\/p>\n

Here, the Pacific plate dives westwards beneath the Australia plate, forming the Tonga trench. Below is a schematic illustration showing what these plates may look like if we cut into the Earth and viewed this subduction zone from the side. Note the Pacific plate on the right and the Australia plate on the left, with the megathrust subduction zone fault where they meet.<\/p>\n

This illustration shows where earthquakes may happen along this plate boundary. There could be interface earthquakes along the megathrust fault (megathrust earthquakes). These are what most people are familiar with when they are thinking about tsunami (e.g., the 2011 Great East Japan Earthquake and Tsunami<\/a>).<\/p>\n

In the upper plate (the Australia plate), there can be crustal fault earthquakes. In the lower plate (the Pacific plate) there can be slab earthquakes (events within the crust, aka the slab), and there can be outer rise earthquakes).<\/p>\n

The outer rise is a part of the plate that is warping up and down because of the forces adjacent to the subduction zone. This warping can cause extension in the upper part, and compression in the lower part, of this plate.<\/p>\n

This 11 Nov 2022 M 7.3 earthquake was a compressional (reverse) earthquake in the outer rise region of this plate boundary. It was pretty deep (for oceanic crust) so fits nicely in the correct place in this illustration:<\/p>\n


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But megathrust earthquakes are not the only type of earthquake that can cause a tsunami. The 2009 magnitude M 8.1 extensional (normal) fault earthquake near Samoa and American Samoa caused a tsunami that inundated the nearby islands (causing lots of damage and human suffering). This tsunami also travelled across the Pacific Ocean to impact California! (This is why the California Tsunami Program monitors tsunami across the Pacific Basin, so that we can help reduce suffering through the evacuation of coastal areas. Remember, the entire coast of California is a Tsunami Hazard Area<\/a>.)<\/p>\n

Below is my interpretive poster for this earthquake<\/font><\/H2><\/p>\n