MSGID: 1:317/3 644362e4
PID: hpt/lnx 1.9.0-cur 2019-01-08
TID: hpt/lnx 1.9.0-cur 2019-01-08
 Ridgecrest faults increasingly sensitive to solid Earth tides before
earthquakes 

  Date:
      April 21, 2023
  Source:
      Seismological Society of America
  Summary:
      Faults in the Ridgecrest, California area were very sensitive to
      solid earth tidal stresses in the year and a half before the July
      2019 Ridgecrest earthquake sequence.


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FULL STORY
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Faults in the Ridgecrest, California area were very sensitive to
solid earth tidal stresses in the year and a half before the July 2019
Ridgecrest earthquake sequence, researchers reported at the Seismological
Society of America (SSA)'s 2023 Annual Meeting.


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"The signal of tidal modulation becomes extremely strong" after 2018,
said Eric Beauce of Lamont-Doherty Earth Observatory, who noted that the
signal was identified with seismicity that occurred around the faults
that broke in the 2019 magnitude 7.1 earthquake.

The link does not mean that tidal stresses -- which are very small
compared to other tectonic stresses -- triggered the earthquake, however.

"We don't know if something started to happen in the fault zone,
something that is an indicator of the upcoming earthquake," Beauce
said. "Maybe that process changed the properties of the crust in a way
that made the crust be more sensitive to tidal stresses."  Pulled by
the same gravitational forces of sun and moon that create ocean tides,
the solid earth also deforms in the same periodic way. People can't feel
the changes, but the ground deforms between 10 to 20 centimeters a day.

These solid tides "induce very, very small stress changes in the crust,"
Beauce explains, "which can induce stress changes in all the faults
within the crust."  Although researchers have known about these tiny
stress changes for more than a century, it has been difficult to extract
their signal from the seismic record, and to determine whether they
modulate seismicity.

In the past ten years, however, better earthquake detection and analysis
techniques have made it possible to search through earthquake catalogs
to find the signal of tidal stresses, Beauce said.

He and his colleagues built a rich, high-resolution earthquake catalog,
using machine learning algorithms along with other techniques, for the
past decade of microseismicity in the Ridgecrest area. (Microseismicity
usually refers to earthquakes of magnitude 2.0 or smaller).

They found that "there is suggestive evidence that peak seismicity happens
when tidal stresses are maximum," Beauce said, "but this modulation is
weak, and because it is weak, it is only suggested."  Other researchers
looking at the 2004 Indian Ocean and 2011 Tohoku megathrust earthquakes
have detected an increase in modulation of seismicity connected to
tidal stresses, decades before the earthquakes, said Beauce. And some
scientists have been able to generate similar results in lab-created
earthquake experiments.

The tidal findings do not have direct implications for earthquake
forecasting, "as we do not know if we are looking at a general phenomenon
or one specific to the Ridgecrest earthquake only, said Beauce, "but I
see it as a way of getting new observational constraints on the physics
of earthquakes, possibly the preparation and nucleation of earthquakes."
    * RELATED_TOPICS
          o Earth_&_Climate
                # Earthquakes # Natural_Disasters # Tsunamis # Geology #
                Earth_Science # Near-Earth_Object_Impacts # Geography
                # Oceanography
    * RELATED_TERMS
          o Geologic_fault o 1976_Tangshan_earthquake o
          1906_San_Francisco_earthquake o Tide o Earthquake
          o Making_existing_structures_earthquake_resistant o
          2004_Indian_Ocean_earthquake o Structure_of_the_Earth

==========================================================================
Story Source: Materials provided by
Seismological_Society_of_America. Note: Content may be edited for style
and length.


==========================================================================


Link to news story:
https://www.sciencedaily.com/releases/2023/04/230421092025.htm

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