M6.8 and M6.3 east of Mindanao, Philippines

[Astronuc]

M 6.8 - 18 km ENE of Barcelona, Philippines​

(was reported initially as M6.7)
https://earthquake.usgs.gov/earthquakes/eventpage/us6000nhqc/executive

• 2024-08-02 22:23:01 (UTC)
• 8.193°N 126.600°E
• 25.8 km depth

M 6.3 - 36 km E of Barcelona, Philippines​

https://earthquake.usgs.gov/earthquakes/eventpage/us6000nht0/executive

• 2024-08-03 04:20:26 (UTC)
• 8.170°N 126.764°E
• 15.9 km depth

Many smaller earthquakes in the vicinity in the M4.4 to M5.3 range. No tsunami warning issued.

https://www.voanews.com/a/magnitude-earthquake-hits-off-philippines-mindanao-island/7728430.html

 

[jedishrfu]

A "no tsunami warning issued" means there was no activity in the water to be concerned about, such as an underwater earthquake or a landslide into the water, right?

 

[Astronuc]

A "no tsunami warning issued" means there was no activity in the water to be concerned about, such as an underwater earthquake or a landslide into the water, right?

Right, there would have been no significant displacement of a volume of earth (subsea surface) and/or volume of water. The displacement could have been lateral, instead of vertical, and there was no apparent underwater slide, or if there was, it was away from Mindanao.

Maybe @davenn can comment.

 

[jedishrfu]

I also found that the issuing authority might also decide to issue a warning under the following conditions:

1. Detection of an Undersea Earthquake: A warning may be issued if an undersea earthquake of significant magnitude (typically 7.5 or higher) is detected, particularly in areas known for producing tsunamis.

2. Unusual Sea Level Changes: If significant and unusual sea-level changes are observed, such as rapid rises or falls, this may indicate that a tsunami has been generated, and a warning will be issued.

3. Reports of Tsunami Activity: Credible reports of tsunami activity, such as from coastal residents, ships, or buoys, can trigger a tsunami warning.

4. Confirmation from Tsunami Detection Systems: Tsunami detection systems, such as deep-ocean buoys or coastal tide gauges, can confirm the presence of a tsunami. If these systems detect a tsunami, a warning will be issued.

5. Historical Data and Tsunami Models: If the conditions match those of previous events that have produced tsunamis and models predict a potential tsunami, authorities may issue a warning.

 

[davenn]

. The displacement could have been lateral, instead of vertical, and there was no apparent underwater slide, or if there was, it was away from Mindanao.

Maybe @davenn can comment.

1. Detection of an Undersea Earthquake: A warning may be issued if an undersea earthquake of significant magnitude (typically 7.5 or higher) is detected, particularly in areas known for producing tsunamis.

hi guys,
yes, tho this was a thrust fault, which are the ones that cause most tsunamis, at M6.8, it's well below the magnitude of what would normally cause a tsunami. below the "beachball focal mechanism for the 6.8
main shock. It is mostly thrust ( reverse faulting) with a very small component of strike-slip. Hence why the blue area is offset vertically. With north at the top, the thrust direction was to the WNW ( roughly in a line between the P and the T.

That M7.5 mentioned above is a pretty good guideline for quake size and tsunami generation.

I only recall one M7 quake that produced a significant tsunami. It was on the north coast of New Guinea
On July 17, 1998, a 7.0 magnitude (Mw) earthquake struck the island of Papua New Guinea at 5:49 p.m.
local time.
PNG quake and tsunami

With an up to 15m of run-up. It has been suggested, for various reasons, that the 7.0 triggered an
under-sea land slide that caused a large water colum offset to produce the tsunami.
That article covers it well.

cheers
Dave