Category: Uncategorized

The Tofino cluster is named for the village of Tofino on the west coast
of Vancouver Island, Canada. As with many calibrated clusters along
coastlines, azimuthal coverage is a major problem, ameliorated somewhat
in this case by the availability of observations for some events from
ocean bottom seismometers. About half the events in the cluster are
observed only to regional distances but they are retained to provide a
sufficient number of local-distance readings to adequately constrain the
crustal velocity structure and depth constraint. Similarly, about half
the events are beneath the Moho (30 km) of the crustal model, to a
maximum depth of 45-50 km. Even though there are only two events with
magnitude 5.0 or greater (the largest is 5.7) the cluster does have
reasonable coverage at teleseismic distances. All events have depth
control from near-source or local-distance observations, and a few also
have teleseismic depth phases for corroboration.

The Haida cluster is named for the Haida Gwaii region off the west coast
of Canada. The cluster includes some earthquakes on the Queen Charlotte
Fault (QCF), which runs along the southwest edge of Haida Gwaii. Most of
the earthquakes on the QCF have azimuthal coverage that is too weak for
stable, robust locations. Prior to about 1990 there were too few seismic
stations in the area to support high quality relocation analysis.
Station coverage is quite good for earthquakes on Graham Island (the
more northern of two main islands comprising Haida Gwaii) and in the
sound between Haida Gwaii and the mainland. All events have depth
control, most from near-source and local-distance readings, and a few
events have teleseismic depth phase observations. The cluster retains
some events observed only to regional distances, but many events have
teleseismic observations.

The Penasco cluster is named for the city of Puerto Peñasco at the
northern end of the Gulf of California, Mexico. It covers approximately
the northernmost quarter of the length of the Gulf. Earthquakes range up
to mid-5 in magnitude. Because of the geometry of seismicity in the
middle of the Gulf and seismograph stations on either coast, few events
have near-source observations for depth control. As might be expected
for an immature oceanic spreading system the crustal velocity structure
(25 km thick) is thinner than normal continental crust but thicker than
true oceanic crust. All events have depth constraint, mainly from
local-distance readings, but some from teleseismic depth phases and
waveform modeling. The distribution of seismograph stations provides
good azimuthal coverage and the location calibration is quite robust.

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.