Earth tremor

Chat and items of interest about Crete and Greece.
Andy
Posts: 42
Joined: Tue Oct 30, 2018 9:25 am
Location: Epano Sisi

Re: Earth tremor

Postby Andy » Tue Sep 28, 2021 7:39 am

My seismometer detected it, i.e. a three shade ceiling light fitting with the shades at slightly different heights so they are not touching but can touch if they swing.


We have several sets of indoor windchimes that serve the same purpose. They detected this mornings 5.3 but since we were upstairs we felt nothing. The lower floor of our house is below ground effectively set into the bedrock. We have two desks that I always align with each other after each tremor, this morning I found them 5cm apart. Yesterday we were downstairs and had to hold on to the 4 computer monitors standing on the desks :shock:

Kilkis
Posts: 13083
Joined: Sat Apr 21, 2007 3:58 pm
Location: Near Chania

Re: Earth tremor

Postby Kilkis » Tue Sep 28, 2021 8:17 am

You are much closer to the epicentre than me, Andy, so I am not surprised you felt it very strongly.

Warwick

TweetTweet
Posts: 466
Joined: Fri Jan 13, 2012 10:35 am

Re: Earth tremor

Postby TweetTweet » Tue Sep 28, 2021 8:56 am

Kilkis wrote:What you experience is a mixture of exactly how the plates have moved and the geometry of where the epicentre is relative to you. I've experienced up and down motion and side to side in Chania but always at a very low level.

For example the 2004 Indian Ocean Tsunami was so big because one section of plate suddenly displaced vertically relative to the adjacent one putting a vertical pulse into the water. Sometimes one plate is sliding under another at an angle, i.e. a subduction zone, and sometimes they are sliding horizontally parallel to each other.

For buildings built with reinforced concrete pillars to resist earthquakes vertical movement is generally reckoned to be worse than lateral movement. Concrete is excellent in compression but has little strength in extension. For vertical movement you are totally relying on the rebar when the movement tries to stretch the column. For horizontal movement the vertical columns are trying to bend. That puts one side of the column in extension but the other side in compression so the strength of the concrete in compression helps resist damage.

Warwick


Thank you for that very good explanation.

This morning's 5.3 felt pretty strong and seemed to go on forever!

TweetTweet
Posts: 466
Joined: Fri Jan 13, 2012 10:35 am

Re: Earth tremor

Postby TweetTweet » Tue Sep 28, 2021 9:10 am

Kookla wrote:I’ve since read TweetTweet, that National and International sites vary on their grading. A couple more this afternoon, where I briefly left the office as it is old and built well before any laws on earthquake requirements were made. I’ve just had another look at the same site and it lists about 47 today in the same-ish area.


Yes, they do seem to vary.

https://www.usgs.gov/faqs/why-do-usgs-e ... e_products

"Magnitude estimates for a given earthquake can vary between reporting agencies due to differences in methodology, data availability, and inherent uncertainties in seismic data. Individual agencies use magnitude estimation procedures designed to meet the agency's specific needs and monitoring capabilities. Even for well-recorded events, differences in magnitude of 0.2 or 0.3"

I also read (somewhere) that the Richter scale is no longer used so much.

I hope the unexpectedly homeless families from Arkalochoris will be looked after.

Kilkis
Posts: 13083
Joined: Sat Apr 21, 2007 3:58 pm
Location: Near Chania

Re: Earth tremor

Postby Kilkis » Tue Sep 28, 2021 11:00 am

There are lots of different scales now used depending on exactly what is measured. They have a couple of things in common:
    1 They are all logarithmic with an increase of +1 on the scale representing an increase of 10x in amplitude or approximately 32x in energy.
    2 They are normalised so that they all approximately agree for a Richter value of 6.
Richter was based on the total amplitude of all the different waves combined measured relatively local to the epicentre. Most of the other scales now single out specific types of wave and measure their amplitude individually. Because the different types of wave have different propagation characteristics they tend to give different results depending on how far away the measuring site is from the epicentre.

Warwick

Kamisiana
Posts: 519
Joined: Tue Jul 25, 2017 4:06 pm
Location: Timbuctuish

Re: Earth tremor

Postby Kamisiana » Tue Sep 28, 2021 12:32 pm

Be prepared for the next one :wink:
https://www.earthquakecountry.org/step5/

Kookla
Posts: 217
Joined: Sun Mar 27, 2016 4:24 pm

Re: Earth tremor

Postby Kookla » Thu Oct 07, 2021 12:19 pm

Well I’m learning something new, I had no idea that there were so many faults on Crete.

https://www.apokoronaslife.gr/%CE%B1%CF ... 3585085%26

evansmr1
Posts: 395
Joined: Tue Nov 09, 2010 3:00 pm
Location: Pirgos, Kalo Horio,

Re: Earth tremor

Postby evansmr1 » Thu Oct 07, 2021 1:48 pm

Nothing felt around the Agios Nikolaos area.

But I wish sometimes the earth would move for me :cry:
Mike
=============
Sic parvis magna

Tim
Posts: 750
Joined: Sun Feb 19, 2012 1:41 pm
Location: Near Sitia
Contact:

Re: Earth tremor

Postby Tim » Tue Oct 12, 2021 11:36 am

evansmr1 wrote:Nothing felt around the Agios Nikolaos area.

But I wish sometimes the earth would move for me :cry:


Bet you felt THAT one, though! I thought the house was going to fall down ...

Tim

Kilkis
Posts: 13083
Joined: Sat Apr 21, 2007 3:58 pm
Location: Near Chania

Re: Earth tremor

Postby Kilkis » Tue Oct 12, 2021 11:54 am

Again very slight movement down the west.

Warwick

Tim
Posts: 750
Joined: Sun Feb 19, 2012 1:41 pm
Location: Near Sitia
Contact:

Re: Earth tremor

Postby Tim » Tue Oct 12, 2021 12:05 pm

Magnitude 6.4 according to the USGS. Near Paleokastro. It was one hell of a shake!

Tim

Kookla
Posts: 217
Joined: Sun Mar 27, 2016 4:24 pm

Re: Earth tremor

Postby Kookla » Tue Oct 12, 2021 12:15 pm

Yes I felt it too.(Stylos area Apokoronas) To use my new found technical jargon; (thanks for all the info Warwick)...it was very much a sideways wobble!
23 km east of Zakros, depth about 8.2 km 6.3R


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