Category: Uncategorized

The Fes cluster is named after the city of Fes (Fez) in northern
Morocco. The sparse distribution of seismograph stations and the diffuse
and generally low level of seismicity made it necessary to encompass a
fairly large region for this cluster. Most events are small and recorded
only to regional distances but there is a modest number of teleseismic
arrivals. All events have depth control from near-source and
local-distance readings, teleseismic depth phases or waveform analysis.
The range of depths observed in this cluster is larger than usual, with
events from very shallow depths down to around 50 km.

The Bigadiç cluster is named for the town of Bigadiç in Balıkesir
Province, western Turkey. The cluster is formed around a 6.1 Mw
earthquake on August 10, 2025 which was followed on October 27, 2025 by
a 6.0 Mw event about 13 km to the southeast. The cluster also includes
the 5.9 Ms Demirci earthquake on March 23, 1969. The station
distribution in the region is very dense and the location calibration is
very robust. All events have depth control from near-source and
local-distance readings, teleseismic depth phases or waveform analysis.

The Chamoli cluster has been redone using recently-acquired data from a temporary network and making use of differential time data. The chamoli16 cluster contains 546 events, compared to 44 events in chamoli11.

The Chamoli cluster is named after the Chamoli District of Uttarakhand
State, India. The cluster contains two damaging earthquakes in the
district, the Mw 6.8 Uttarkashi earthquake on October 19, 1991 and the
Mw 6.6 Chamoli earthquake on March 28, 1998. This version of the Chamoli
cluster replaces the chamoli11 version previously uploaded to GCCEL.
This version takes advantage of the ability to relocate a much larger
number of events and includes a large number of small events that were
well-observed by two temporary networks, one in 19990328-19990617 (data
provided by Bal Rastogi) and another in 20171127-20211016 (data provided
by Jyotima Kanaujia). The arrival time data for these small events
establishes a very robust direct calibration analysis, using 11,164
arrivals within 0.8° to locate the hypocentroid. Another reason for
retaining these locally-recorded events is to make their data more
widely available for research. All events have depth control from
near-source and local-distance readings, or teleseismic depth phases.
The relocation also utilizes 293 measurements of differential times of
regional and teleseismic phases made by Benjamin Kohl.

mloc v13.0.4 may now be downloaded from the mloc distribution page of this website. The User’s Manual has been updated and can be downloaded here. The main differences from the previous distribution (v13.0.2) are related to the handling of differential time data.

The Kunar cluster is named for Kunar Province in the lower Hindu Kush
Mountains of eastern Afghanistan. The cluster is based on a devastating
6.0 Mw earthquake on August 31, 2025, and includes a 6.2 Mw earthquake
on February 1, 1984. Location calibration of this cluster is done with
the indirect method, taking advantage of InSAR models produced for the
mainshock and a 5.5 Mw aftershock on September 4. These models indicated
that the rupture was quite shallow, less than 10 km, a finding confirmed
by detailed waveform studies of the mainshock and largest aftershock.
The calibration shift for epicenters is 10.7 km at an azimuth of 250°.
Calibration of the origin time of the cluster is based on observations
of Pg and Sg arrivals at stations to the west (KBL and KBU) and east
(mainly CEP) of the cluster at distances of 0.5° to 1.5° epicentral
distance. The crustal velocity model was found to require a crustal
thickness of ~60 km, so direct-arriving crustal phases can be observed
at greater distances than usual. Resolution of the depth and origin time
calibration for this cluster is weaker than usual because of the
scarcity of seismological data. Resolution of relative locations is
improved for some events by the use of differential time measurements
provided by Will Yeck (NEIC). All events have depth control, mainly from
local distance arrivals.

The Kamchatka cluster is named for the Kamchatka Peninsula in the far
east of Russia, and covers the subduction zone along southern
Kamchatka’s Pacific coast. The region is intensely active, most notably
with the 9.0 Mw earthquake of Novermber 4, 1952 and the 8.8 Mw
earthquake of July 29, 2025. The cluster includes both earthquakes
(indicated by larger red stars in the base map), as well as the
September 13 (7.4 Mw) and September 19 (7.8 Mw) aftershocks of the 2025
mainshock, indicated by smaller red stars in the base map, but the point
of this cluster is not to represent the full pattern of seismicity in
the region; it is to provide a framework of calibrated hypocenters which
can be a reference point for more detailed studies of the seismicity. As
in most subduction zone settings, most of the seismicity in southern
Kamchatka is off-shore and therefore is not amenable to direct
calibration because of poor azimuthal coverage. However, by careful
selection of earthquakes, including events that occurred at greater
depths (to ~190 km) in the subduction zone, a cluster with good
azimuthal coverage for direct calibration can be assembled. It is
possible to add additional events to this kernel, of course, but adding
too many offshore events destabilizes the location calibration and even
if that were not the case, the shear number of large earthquakes in this
region overwhelms the computational capacity of the relocation code.
Therefore the strategy for placing more of the seismicity of this
important seismic zone in a location-calibrated context is to first
establish this calibrated framework which includes well-recorded events
from 1952 through 2025. Then subsets of the seismicity in the southern
Kamchatka subduction zone, such as a fuller representation of the 1952
sequence, can be relocated with calibrated locations through the
indirect calibration process, making use of the reference locations
determined in this cluster. All earthquakes in the cluster have depth
control, often from both direct arrivals at short epicentral distance
and from teleseismic depth phases. After the 1952 and 2025 mainshocks,
events are selected mainly on the basis of being well-recorded
teleseismically and also having observations at local seismograph
stations that provide the azimuthal coverage needed for a stable direct
calibration. Another criterion is temporal continuity from 1952 through
2025, so that the cluster adequately represents the evolving network of
regional and global seismograph stations. Direct calibration is based on
a simplistic flat-layered crustal model which is obviously a poor
representation of the true velocity structure of a subduction zone. To
some extent the resulting increased scatter in residuals is reflected in
the uncertainties of hypocentral parameters but there is undoubtedly
some remaining systematic bias in the hypocenters.

The Anchor cluster is named for Anchor Point at the western end of the
Kenai Peninsula, Alaska. The cluster spans the Cook Inlet. It includes
events in two depth ranges, events shallower than ~25 km, mainly along
the coast of the Alaskan mainland on the west side of Cook Inlet and
events in the range 30-65 km on the eastern side of Cook Inlet, and
beneath the western coast of the Kenai Peninsula. Many events are small
and only observed to regional distances, but all events are observed to
at least 5° epicentral distance. All events have depth control from
near-source and local-distance arrival times.

The Simav-Gediz cluster is named for two significant earthquakes in
central Turkey, the 7.2 Mw Gediz earthquake on March 28, 1970, and the
5.9 Mw Simav earthquake on May 19, 2011. Initial work on these clusters
was done by Ezgi Karasözen. The cluster includes both sequences as well
as other well-recorded events in the vicinity. All events were recorded
to at least 10° epicentral distance and most were recorded
teleseismically. The seismograph network in this area was sparse before
about 2007, but quite dense afterwards, so all events after that time
have depth control from near-source and local-distance readings. Depth
control for earlier events is a mixture of local-distance readings,
teleseismic depth phases, and, in 17 cases lacking any other constraint
(all prior to 1977), a default depth sampled from a probability density
function that was based on the distribution of events with depth
constraint. The probability density function has a peak at 9 km and a
spread of 2.5 km. Sampled depths are required to be within 2-sigma of
the mean (i.e., 4-14 km).

The distribution of mloc v13.0.2 was posted today. It can be downloaded from https://seismo.com/mloc/distribution/. The accompanying Desktop User’s Manual can be downloaded from https://seismo.com/mloc/desktop-manual/.

Due to extensive changes to the source code since the last distribution, cohesion between the current version of mloc and the User’s Manual is not as complete as I would like. I will be glad to be informed of places in the Manual that need further work.

The Oran cluster is named for the city of Oran on the Mediterranean
coast of Algeria. It includes a few events across the border in coastal
Morocco. The cluster contains four events with magnitude > 5, the
largest being the 5.5 Mw event on June 6, 2008. Most events were
observed to teleseismic distances but some smaller events that were
recorded only to near-regional distances were retained to improve the
azimuthal coverage and statistical power of the location calibration.
All events have depth control, from near-source or local-distance
readings, or in a several cases, a waveform modeling study or
teleseismic depth phases.