10 Aug 2015 a significant quake M 6.6, Solomon Isl

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Discussion Overview

The discussion centers around significant seismic events in the Solomon Islands, specifically focusing on a magnitude 6.6 earthquake that occurred on August 10, 2015. Participants share observations from seismographs, inquire about the measurements, and discuss the characteristics of seismometers.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant reports a Mw 6.6 earthquake located 180km SW of Dadali, Solomon Islands, and mentions a preceding M 5.2 quake near Raoul Island, Kermadecs, NZ.
  • Another participant questions whether the deflection of the seismograph needle corresponds to a specific ground movement measurement, seeking clarification on the relationship between needle movement and actual ground displacement.
  • A participant explains the functionality of their Force Balanced Vertical seismometer, detailing its sensitivity and output characteristics, including the distinction between ground velocity and displacement measurements.
  • Additional reports of significant quakes in the Solomon region are shared, including a Mw 6.4 quake and another M 6.6 quake near Santa Cruz Island.

Areas of Agreement / Disagreement

Participants express interest in the seismic events and share information, but there is no consensus on the specifics of measurement interpretations or the implications of the reported quakes.

Contextual Notes

Participants discuss the sensitivity and limitations of the seismometer, including its ability to filter out noise and detect various seismic events, but do not resolve the implications of these characteristics on data interpretation.

davenn
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Mw 6.6 180km SW of Dadali, Solomon Islands 2015-08-10 04:12:14 UTC

from my seismograph located in Sydney, Australia ...

150810 0412UT M6.6 Solomon Isl reg zhi.gif


the event below it was a M 5.2 NE of Raoul Is, Kermadecs, NZ
Dave
 
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Cool.

Does the deflection of the needle translate into some value with a unit? i.e. does an 10 millimeter spike correspond with a 10 centimeter ground movement, or some such correlation?
 
Hi Dave,

the seismometer used in the above recording is a Force Balanced Vertical seismometer
These record ground velocity rather than displacement

on this page you will see pic's of a completed one as well as one during assembly
Dale, the page owner build and calibrated my unit The instrument's final cost to me was AU$550

the spec's for the instruments he builds are ...

FBV INYO specifications


  • The instrument's high-gain output has a sensitivity of approximately 315 V/cm/sec (31,462 V/m/sec) over a frequency range of 50 seconds to 30 Hz, while the low gain output is 6.29 V/cm/sec (629 V/m/sec) over the same bandwidth. Both outputs clip at a level of 10 Volts, which represents 318μm/sec for the high gain channel and 1.59cm/sec for the low gain one.

    High gain channel

    354nm/sec/line *WinSDR Y-scale factor = 1 50sec – 12.5sec (0.08Hz) Clipping level 318μm/sec.

    These settings greatly reduce microseisms and cultural noise although they also eliminate higher-frequency local quakes and may mask some phases of teleseisms. However the sensitivity is sufficient to occasionally display surface waves originating from distant quakes having magnitudes in the high 4's, low 5's. Large quakes will be off screen, although the channel clipping level (10V out) is still 318μm/sec. or 36x this screen height.

    Low gain channel

    17.7μm/sec/line WinSDR Y-scale factor = 1 50sec – 10Hz Clipping level 1.59 cm/sec

    These settings clearly show some cultural noise, which tends to get smaller at night. Higher-frequency local quakes show up well on this display and large teleseisms are also well displayed.
* WinSDR is the datalogging software/hardware

Dave
 
another significant quake from the Solomons region this morning
Mw 6.4

150812   UT M 6.4 S of Gizo, Solomons zhi.gif
 
yet another significant quake in the Solomons reg
M 6.6 SW of Santa Cruz Isl

150815 0747UT M 6.6 SW of Lata, Santa Cruz Is zhi.gif
 

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