Category: Uncategorized

The Alberchigos cluster is named for the town of Albérchigos in
northwestern Baja, Mexico. The earthquakes are mostly small; the largest
event is 5.3 Mw on August 17, 2020. Only events that were recorded to at
least 5° epicentral distance are retained. Teleseismic arrivals are
scarce beyond 40°. The seismograph network in the region is quite dense
since ~2005 and the location calibration is very robust. All events have
depth control from near-source and local-distance readings.

The Kodiak cluster is named for Kodiak Island in the Aleutian Island
chain of Alaska. The distribution of seismograph stations in the region
requires that the cluster be rather large, geographically, and it is
necessary for robust location calibration to include earthquakes deep in
the subduction zone, to depths of ~160 km, which provides raypaths to
the northwest for good azimuthal coverage. The cluster contains many
events in the magnitude 5-6 range, but no events of magnitude 7 or
greater. Some events are only recorded to far regional distances. All
events have depth control, often from near-source and local-distance
arrivals as well as teleseismic depth phases, and in many cases,
waveform modeling.

This version of the Simeonof cluster (simeonof10) replaces the simeonof6 cluster.

The Simeonof cluster is named for Simeonof Island, in the Shumagin
Islands group of the Aleutian Islands, southern Alaska, U.S.A. It
includes the magnitude 7.8 Mw and 7.6 Mw Simeonof earthquakes on July 22
and October 19, 2020, and the 7.2 Mw earthquake on July 16, 2025. All
events have depth control, primarily from arrival time observations at
stations at near-epicentral and local distances and many of the larger
events also have depth control from teleseismic depth phases. There are
many cases with both types of constraint in which the agreement is very
good. The ability to calibrate the location of this cluster depends
heavily on including deeper events (to ~60 km) that provide raypaths to
the north and northwest, balancing the raypaths to events offshore to
the southeast.

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.