=Paper=
{{Paper
|id=Vol-3006/23_short_paper
|storemode=property
|title=Creepex as a parameter of seismo-geodynamic studies based on geo-information systems
|pdfUrl=https://ceur-ws.org/Vol-3006/23_short_paper.pdf
|volume=Vol-3006
|authors=Anna V. Mikheeva,Igor I. Kalinnikov
}}
==Creepex as a parameter of seismo-geodynamic studies based on geo-information systems==
https://ceur-ws.org/Vol-3006/23_short_paper.pdf
Creepex as a parameter of seismo-geodynamic studies
based on geo-information systems
Anna V. Mikheeva1 , Igor I. Kalinnikov2
1
Institute of Computational Mathematics and Mathematical Geophysics SB RAS, Novosibirsk, Russia
2
Institute of Physics of the Earth of O.Yu. Schmidt RAS, Moscow, Russia
Abstract
The GIS-EEDB (the Expert Earthquake Database) and GIS-ENDDB (the Earth’s Natural Disasters
DataBase) geoinformation systems implement methods for spatial-temporal analysis of both classi-
cal and new characteristics of the seismogeodynamic process. One of the new characteristics is a
normalized creepex parameter that can be used in the statistical approach to studying of seismicity to
assess a relative contribution of “soft” (creep) and “hard” (explosion) movements to the overall process
of focal radiation. In this paper, the following modifications of the creepex parameter are proposed
and compared: 1) 𝐶𝑟0 − 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 and 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 as the result of reducing the parameters
𝐶𝑟0 and 𝐶𝑟𝑁 of each event to the world average values of the creepex, obtained from the polynomial
dependence of 𝐶𝑟𝑖_𝑤𝑜𝑟𝑙𝑑 (𝑖 = 0, 𝑁 ) on 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 , where 𝐶𝑟𝑖_𝑤𝑜𝑟𝑙𝑑 are calculated based on the world
average estimates of 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 and 𝑚𝑏_𝑤𝑜𝑟𝑙𝑑 at uniform intervals of the seismic moment (NEIC catalog),
2) 𝐶𝑟_𝑏𝑗𝑖 as the result of reducing 𝐶𝑟𝑁 of each event to 𝐶𝑟𝑁 _𝑏𝑗𝑖 , i.e. to the average for the studied in this
work BJI catalog creepex values obtained from the polygonal trend 𝐶𝑟𝑁 (𝑀𝑆 ) of all the catalog events.
The advantage of using the creepex parameter, reduced to the trend of averaging the magnitudes of the
catalog in question, is revealed, since the smallest linear dependence of the creepex on the magnitude is
achieved (in comparison with the classical and normalized creepex) and the symmetry in the maximum
amplitude of the deviation of the parameter relative to zero is preserved. Examples of the application of
the compared parameters in specific seismic-geodynamic studies of aftershock processes of the Molucca
and Simushir earthquakes also demonstrate the advantage of the parameter 𝐶𝑟_𝑏𝑗𝑖 in the observed
correspondence of the variations of the latter to the known physical processes in the focal zone of the
Kashmir event, studied by the seismic-geodynamic methods of the GIS-EEDB geographical information
system.
Keywords
Catalogs and databases of earthquakes, seismic and geodynamic processes, tectonic environments.
1. Introduction
At the present time, several modifications and prototypes of GIS-EEDB (the Expert Earthquake
Database) and GIS-ENDDB (the Earth’s Natural Disasters DataBase — a database of disas-
trous events: earthquakes and impact structures) [1] are functioning in various scientific and
educational organizations. Its implement methods of statistical spatial-temporal analysis of
the characteristics of the seismogeodynamic process: both the classical (parameters of the
repeatability graph, the total number of earthquakes, the total seismic energy, methods of
transformation of geophysical fields, etc.) and the new (the relative total seismic energy and
SDM-2021: All-Russian conference, August 24–27, 2021, Novosibirsk, Russia
" anna@omzg.sscc.ru (A. V. Mikheeva); i-kalinn@yandex.ru (I. I. Kalinnikov)
© 2021 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
Workshop
Proceedings
http://ceur-ws.org
ISSN 1613-0073 CEUR Workshop Proceedings (CEUR-WS.org)
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Anna V. Mikheeva et al. CEUR Workshop Proceedings 194–202
its gradients; maximum earthquake depths, the total slip direction in seismic foci, methods
of grouping events into seismolineaments, swarms, clusters; methods of correlation analysis,
etc.). Recently, a method for calculating the normalized creepex was implemented in the GIS
system, which complements the complex seismogeodynamic analysis with maps and graphs
of changes in this parameter in order to identify the relationship of seismic events with the
tectonic environment (by the distribution of its anomalies in space), as well as the regularities
of the seismogenesis processes before and after a strong event (by a change in the parameter in
time).
2. The concept of creepex, its applicability and modifications
A formally constructed parameter of creepex (creep & explosion) is determined by the ratio of
magnitudes 𝑀𝑆 and 𝑚𝑏 :
— by the difference 𝐶𝑟0 = 𝑀𝑆 − 𝑚𝑏 [2] (other types of magnitudes for volume waves are
also allowed [3]);
— by the residual of these magnitudes in the orthogonal regression 𝐶𝑟 = 𝑀𝑆 −𝑘 ·𝑚𝑏 −𝑙 [4].
From a mathematical point of view, a creepex is a difference of quantities of the same dimen-
sion, but with a different physical content. In fact, it is a normalized logarithm of the ratio of
different estimates of the earthquake energy. The energy parameters of MS and mb are deter-
mined by different types (surface and volume) waves at different frequencies (a low-frequency
range for MS: usually with a period of 20 s; and a high-frequency range for mb: usually with a
period of 1 s). The ratio of MS and mb indicates the predominance of low or high frequencies in a
spectrum, indicating macroseismic processes with the creep or the explosion effect, respectively.
This allows the parameter to be used, for example, for reliable explosions identification on the
background of seismic events of natural and anthropogenic origin. The spectral characteristics
of the processes of fast and slow disruptions of the geophysical environment continuity act as
an information carrier in the identification criteria. The extremely fast destruction by explosion
is accompanied by the emission of high-frequency seismic vibrations, the extremely slow one
is by a plastic flow, i.e. a creep, which in the extreme case is not accompanied by the high-
frequency seismic emission (episodic tremor and sliding). But the information content of the
creepex is much broader, since 𝑀𝑆 and 𝑚𝑏 are evaluated by seismologists based on the spectral
characteristics of the wave forms associated with an earthquake, each reflecting the specific
features not only of an earthquake itself, but also the conditions of its origin and propagation in
the “muddy” (according to [5]) geophysical environment.
Thus, 𝐶𝑟0 and 𝐶𝑟 are those simple parameters of the spectral characteristics of the earth-
quakes that can be used in the statistical approach to studying of seismicity to assess a relative
contribution of “soft” (creep) and “hard” (explosion) movements to the overall process of focal
radiation. Thus, the dominance of increased values of the creepex in the region under study,
reflecting the predominance of low frequencies in the earthquake spectrum, is a sign of tectonic
“softness” [3]. Indeed, in [6, 7], it is confirmed that in transform faults with a shift deformation
or spreading zones, the tectonic movement in which generally exhibits the property of “aseismic
creep”, seismic sources have a much higher value of the creepex than in subduction zones
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characterized by a “cold” brittle fracture. On the other hand, the reason for the local differences
in the creepex distributions “be sought for in different conditions for generating seismic waves
in specific foci — the type of strength or mechanism of the focus” [2, 3]. This means that local
𝐶𝑟 deviations are “a measure of the specificity of the focal zone”, and spatial-temporal changes
in the parameter will be “due to the conditions variations in the focal zone on the radiation of
compression and shift waves” [7]. However, a “balanced” approach is also necessary here, since
the accuracy of the 𝐶𝑟 estimate for an individual event, determined by the error in calculating
𝑀𝑆 and 𝑚𝑏 , can be “both objective and subjective” [7, 8].
There are many factors leading to the dependence of the radiation efficiency of a seismic source
on the scope of events, for example, the effect of absorption and scattering of high frequencies
during the oscillations propagation [9]. In addition, there are some methodological problems in
estimating the seismic energy of earthquakes, for example, its systematic overestimation in an
elastic medium in comparison with a viscoplastic one [10], etc. Such factors can be the reason
for the long-discovered nonlinearity of relationships between magnitudes of different types [11].
Thus, studying earthquake catalogs created by many agencies has shown that the difference
between the magnitudes 𝑀𝑆 and 𝑚𝑏 depends on the earthquake magnitude 𝑀𝑆 according to
the linearly growing law [3, 8]. This dependence complicates the use of the creepex parameter
in statistical studies, making it difficult to adequately interpret its anomalies without a special
consideration of the magnitude of each event in a sample.
To solve this problem, a modified (normalized to the arithmetic mean of 𝑀𝑆 and mb of each
event) estimate of the creepex parameter 𝐶𝑟𝑁 = 4(𝑀𝑆 − 𝑚𝑏 )/(𝑀𝑆 + 𝑚𝑏 ) was proposed
in [8] which somewhat reduced its systematic dependence on the earthquakes magnitude 𝑀𝑆
(especially pronounced for large events), but did not completely eliminate this dependence,
transforming it from linear to logarithmic (Figure 1).
In this paper, the following modifications of the creepex parameter are proposed and com-
pared.
1. 𝐶𝑟0 − 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 and 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 is the result of reducing the parameters 𝐶𝑟0
and 𝐶𝑟𝑁 of each event to the world average values of the creepex, obtained from the
polynomial dependence of 𝐶𝑟𝑖_𝑤𝑜𝑟𝑙𝑑 (𝑖 = 0, 𝑁 ) on 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 (Figure 2, a), where 𝐶𝑟𝑖_𝑤𝑜𝑟𝑙𝑑
a
b
Figure 1: The dependence on the magnitude 𝑀𝑆 of the creepex-parameters 𝐶𝑟0 (a) and 𝐶𝑟𝑁 (b) by an
example of the Tohoku earthquake vicinity (1458 paired determinations: 11.03.2010–11.03.2012, 30–50∘ N;
140–160∘ E).
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Anna V. Mikheeva et al. CEUR Workshop Proceedings 194–202
a b
Figure 2: The polynomial dependences: a — on the average world magnitude 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 of the creepex-
parameters: 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 = 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 − 𝑚𝑏_𝑤𝑜𝑟𝑙𝑑 (red) and 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 (blue); b —of the world average
magnitude 𝑀𝑊 on the 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 (green) and of the magnitude 𝑀𝑊 (calculated from 𝑀𝐿 ) on 𝑀𝑆_ (𝑀𝑆
corrected for the trend level) for all the events in the BJI catalog (blue).
are calculated based on the world average estimates of 𝑀𝑆_𝑤𝑜𝑟𝑙𝑑 and 𝑚𝑏_𝑤𝑜𝑟𝑙𝑑 [11] at
uniform intervals of the seismic moment (NEIC catalog).
2. 𝐶𝑟𝑏 𝑗𝑖 — the result of reducing 𝐶𝑟𝑁 of each event to 𝐶𝑟𝑁 _𝑏𝑗𝑖 , i.e. to the average (for the
studied in this work BJI catalog [12]) creepex values obtained from the polygonal trend
𝐶𝑟𝑁 (𝑀𝑆 ) (black line in Figure 2, b) of all the catalog events.
3. Comparative analysis of creepex modifications, examples of
their application
Comparison of the proposed parameters can be carried out both from the view point of solving
the problem of the creepex dependence on magnitude, and based on the correspondence of the
creepex variations to the known physical processes in the foci of specific events, investigated
by different methods of a geographic information system.
The dependence 𝑀𝑆 of different creepex versions is shown in Figure 3 using an example of
the aftershock swarm of the January 21, 2007 earthquake (𝑀𝑆 = 7.5) in Molucca according to
the BJI catalog. The reduced to the average trend of the BJI catalog creepex value 𝐶𝑟𝑁 −𝐶𝑟𝑁 _𝑏𝑗𝑖
demonstrates a less pronounced dependence on magnitude than the parameter 𝐶𝑟𝑁 , while
maintaining the character of monotonic growth with an increase in the magnitude of the event
(Figure 3, a).
On the contrary, the creepexes, reduced to the global data (calculated by NEIC [11]): 𝐶𝑟𝑁 −
𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 and 𝐶𝑟0 − 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 demonstrate (Figure 3, a) the suppression of the monotonic
growth at large magnitudes, resulting in distortion of information about the creepex for large
events. This may be due to a systematic difference in estimates 𝑀𝑆 presented by different
catalogs (here, by BJI and NEIC ones). It is possible, of course, to find the correspondence of
these estimates by the coincidence of the trends in their relationship with a more objective by
defined magnitude 𝑀𝑊 (Figure 2, b). We have estimated the latter according to the magnitude
𝑀𝐿 presented in the BJI catalog. It was found that, in contrast to the dependence 𝑀𝑊 (𝑀𝐿 ):
𝑀𝑊 = 𝑀𝐿 − 0.4 according to Abubakirov et al. [13], for BJI a good agreement of the trends
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a b
Figure 3: Dependence on the magnitude MS of various creepex parameters: 𝐶𝑟𝑁 , 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 ,
𝐶𝑟0 − 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 and 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑏𝑗𝑖 on an example of the aftershock swarm of the earthquake of
21.01.2007, 𝑀𝑆 = 7.5 in Molucca.
in the area of their intersection is given by the formula 𝑀𝑊 = 𝑀𝐿 + 0.5. If we accept
𝑀𝑊 = 𝑀𝐿 − 0.4 [13], then it is necessary to decrease the estimate 𝑀𝑆 in the BJI catalog
by 1.2: 𝑀𝑆_ = 𝑀 𝑆 − 1.2 (Figure 2, b). For 𝑚𝑏 in this case, a correction −0.4 is required.
The introduction of such significant corrections brings about a large shift of the creepex 𝐶𝑟𝑁
value (and, largely, of the value 𝐶𝑟0 ) into the area of negative values. Conversely, reducing the
values 𝐶𝑟0 and 𝐶𝑟𝑁 to average the 𝐶𝑟𝑤𝑜𝑟𝑙𝑑 and 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 world creepexes, obtained from
relatively high magnitudes, leads to a shift of the obtained estimates into the positive area
(Figure 3, b; yellow and gray lines in Figure 4, a). Apparently, the events distribution shifted
in one or another direction does not correspond to the equal importance of the contributions
(to seismicity, in general) of two physical processes: a brittle fracture and a viscous slip. Thus,
from the viewpoint of the expediency of using the creepex, it does not allow to visually classify
events according to relevant two groups using the obtained parameters.
So, the idea of reducing the creepex to the average value over the world catalogs (NEIC) for
the events of the BJI catalog cannot be accepted because, although it removes the dependence of
the creepex on 𝑀𝑆 , leads to a systematic shift of its normalized estimate to the area of negative
or positive values. Now consider the graph in Figure 3, b showing the advisability of reducing
the creepex to the trend of averaging the itself magnitudes of the catalog used, in this case:
𝐶𝑟𝑏𝑗𝑖 = 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑏𝑗𝑖 . The distribution of this parameter (its trend is highlighted by a bold
line) has no displacements about the zero axis.
Examples of the application of the compared parameters in specific seismic geodynamic
studies on various aftershock processes (Figure 4) also demonstrate the advantage of the
parameter 𝐶𝑟𝑏𝑗𝑖 . The first, strongest shock (marked with vertical lines in Figure 4) on the
graphs of 𝐶𝑟𝑁 and 𝐶𝑟𝑏𝑗𝑖 (red and blue colors) is marked by a regular significant increase in
the creepex value (which shows a large contribution of quasi-plastic flow to the mechanism of
main shocks, and sometimes of several subsequent shocks), after which a gradual (over several
hours) decline occurs, characterizing the beginning of the medium conversion to brittle fracture
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a
b
Figure 4: Changes in various creepex parameters in time. a — a 1.5-day fragment of the aftershock
swarm of the earthquake of January 21, 2007, 𝑀𝑆 = 7.5 in the Moluccan Sea, Indonesia (at the
junction of the Eurasian plate and the Papua microplate): 𝐶𝑟𝑁 (red color), 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 (yellow),
𝐶𝑟0 − 𝐶𝑟0_𝑤𝑜𝑟𝑙𝑑 (gray) and 𝐶𝑟𝑏𝑗𝑖 (blue); b — a 0.5-day fragment of the aftershock swarm of the Simushir
earthquake of January 13, 2007, 𝑀𝑆 = 8.1 (at the junction of the Okhotsk and the Pacific plates): 𝐶𝑟𝑁
(red), 𝐶𝑟𝑁 − 𝐶𝑟𝑁 _𝑤𝑜𝑟𝑙𝑑 (yellow) and 𝐶𝑟𝑏𝑗𝑖 (blue).
(developed the next day). A similar mechanism was established as a result of a more detailed
geodynamic study of the Kashmir earthquake (08.10.2005, 𝑀𝑆 = 7.6) carried out by means of
the GIS-ENDDB system (Figure 5).
The temporal distribution of aftershocks of the Kashmir earthquake (Figure 5, a) clearly
demonstrates the relaxation process of the source in the first hours after the main shock by
partial, periodic chains of events with a decreasing value of the creepex 𝐶𝑟𝑁 within a chain.
According to a change in the value 𝐶𝑟𝑁 , the chains demonstrate the transition from quasi-
plastic flow to brittle fracture, according to the general interpretation from [6]. Let us note that a
number of studies [14, 15] mention periodic activations of the after-shock process of the Kashmir
earthquake and the impossibility of explaining its without introducing special corrections into
the seismodynamic model (in particular, the “slip variability” correction, “repeated slip”, etc.) or
the assumption of the existence of a highly fluid layer in the lower crust.
The connection of the initial events of each chain with quasi-plastic processes at depth is also
proved by their depths: the temporal distribution of the ISC catalog events near the focal zone
shows that at the beginning of each chain there is a deeper event than the subsequent ones in
the chain, and the main shock of the Kashmir earthquake, although confined to the depth of
the brittle layer (𝐻 = 8.2 km according to ISC data), is preceded by two foreshocks (3 hours
before the event), which have a greater depth: 15 and 14 km (Figure 5, b). Let us also note that
according to the data of the CMT global catalog [16], the mechanisms of the overwhelming
number of events in the Kashmir earthquake source are an upthrust (Figure 5, c), determined by
the tectonic setting of collisional compression, covering a large range of depths.
The graph of 𝐶𝑟ISC changes over time is more smoothed (the red line in Figure 5, d) than
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a b
c d
Figure 5: Development in time (the first day) of the seismogeodynamic process in the focal zone of the
Kashmir shock (lcreepex catalog containing the paired ISC definitions of 𝑀𝑆 and 𝑚𝑏 ): a — the events
colored by the creepex value 𝐶𝑟𝑁 , where the size of the circles is set by the focal zone size estimated by
𝑀𝑆 [17]; in the inset picture: distribution of these events in the map (all the pictures were obtained by
the GIS-ENDDB analysis system); b — all events of the ISC catalog in the study zone colored by depth
(color and radius are determined by the legend: 𝐻 in km by color, 𝑀𝑆 by size); c — the mechanisms of
the Kashmir earthquakes for 2004–2016: d — a change in the values of 𝐶𝑟𝑁 (blue) and 𝐶𝑟ISC (red) in
the sample of Figure 5, a.
the 𝐶𝑟𝑁 graph (the blue line), since stronger events at the beginning of each chain are not
manifested here by the creepex increase (because there is no proportional dependence of the
creepex on the magnitude). Apparently, the 𝐶𝑟ISC graph more objectively reflects the physical
processes in the focus: the main shock (which is marked by the first point of each chart) does
not show up on the 𝐶𝑟ISC chart as either a positive or a negative maximum. But 1.5 hours after
it, the sharp maximum marks the greatest contribution of the viscous slip to the mechanism of a
pair of synchronous aftershocks (𝑀𝑆 = 5.9 and 𝑀𝑆 = 5.7) located along the perimeter of the
focal zone of the main shock (red and orange circles in the inset picture of Figure 5, a), which
can characterize a sharp change in the environment state caused by the destructive upthrust
of the main shock. Another 5 hours later, an aftershock with 𝑀𝑆 = 6.4 (the beginning of the
second chain of aftershocks in Figure 5, a) occurs just to the northwest of the main shock, which
also does not show up on the 𝐶𝑟ISC chart as a positive maximum, but an hour after which there
is a jump of 𝐶𝑟ISC to the area of positive values (Figure 5, d). It is possible that both of these
maxima show a pattern of occurrence of aftershocks with an increased creepex value after the
largest aftershocks.
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4. Conclusion
The creepex is an informative parameter reflecting the properties of the geophysical environ-
ment, the dynamic processes in which are manifested in the spectral features of waveforms
generated by earthquakes. Obtaining a quantitative measure of information extracted from the
creepex requires taking into account the peculiarities of the used information base: catalog of
earthquakes. This paper shows the advantage of using the creepex parameter, reduced to the
trend of averaging the magnitudes of the catalog in question, since a smaller linear dependence
of the creepex on the magnitude is achieved (in comparison with classical creepex) and a sym-
metry is preserved in the maximum amplitudes of the parameter deviation relative to zero. The
choice of the most informative modification of the creepex parameter and its implementation
into the expert information and computing system GIS-ENDDB will provide the possibility: to
calculate and visualize the distribution of the creepex parameter in space and time; to trace
its retrospective dynamics in various regions, including that in the zones of preparation and
development of strong earthquakes; to identify possible predictive patterns in the resulting
anomalies. For example, the researching Kashmir earthquake (08.10.2005, 𝑀𝑆 = 7.6) by means
of the GIS-ENDDB system demonstrates in terms of the creepex value change the patterns of
medium transition from quasi-plastic flow to brittle destruction after a major shock.
Acknowledgments
This work was carried out under state contract with ICM&MG SB RAS 0251-2021-0004.
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