Download Zaliapin and Ben-Zion - University of Nevada, Reno

Discriminating characteristics of tectonic and human-induced seismicity
SCEC Annual Meeting
September 13-16, 2015
Poster 146
Ilya Zaliapin
Yehuda Ben-Zion
Department of Mathematics and Statistics
University of Nevada, Reno
[email protected]
http://www.unr.edu/~zal
Summary
We show that multiple properties of earthquake clusters reveal distinct signatures of
induced and tectonic earthquakes.
We identify earthquake clusters using nearest-neighbor analysis in time-spacemagnitude domain (Panel 1). We also apply this method to identify the background
and clustered subpopulations of seismicity.
Analyzing "end-member" cases of human-induced earthquakes (the Geyser
geothermal field in northern California and TauTona gold mine in South Africa) and
tectonic earthquakes (San Jacinto fault zone and Coso region with no geothermal
production in eastern central California), we find clear differences between the
relative location of background and clustered events expressed via the magnitudescaled time and distance to the nearest neighbor (Panel 2). The time decay of
offspring is much faster in regions of induced seismicity (Panel 3).
Next, we show that similar differences characterize the seismicity within the Coso
and Salton Sea geothermal fields in California before and after the expansion of
geothermal production (Panel 4). Broad regions like southern California have mixed
signatures of both types of clustering.
Department of Earth Sciences
University of South California
[email protected]
http://earth.usc.edu/~ybz/
2. Time and space components of the nearest-neighbor earthquake distance
Induced
Mixed
Tectonic
Distribution of rescaled time T to parent for the offspring within one parent rupture length from the parent. Notice
bimodal distribution of the rescaled times in induced and mixed regions (panels a-d), vs. unimodal distribution in
tectonic regions (panels e-f).
3. Offspring time decay
1. Data and identification of background/cluster populations
 We use the waveform relocated catalog of Hauksson et al. [2012] in southern California, the double-difference
catalog of Waldhauser and Schaff [2008] in northern California, and seismicity of TauTona golden mine [ISSI].
 Cluster identification is done according to Zaliapin et al. [2008] and Zaliapin and Ben-Zion [2013a]. The method is
based on the earthquake nearest-neighbor distance η in time-space-magnitude domain [Baiesi and Paczuski,
2004] – see Panels 1A,B below. The 2D distribution of the time (T) and space (R) components of the nearestneighbor distance in the observed catalogs is prominently bi-modal (see figure below), with upper mode
corresponding to background seismicity and lower mode to the clustered seismicity [Zaliapin et al., 2008; Zaliapin
and Ben-Zion, 2011, 2013a]. This bimodality is used to separate the earthquakes into background and cluster
populations (see below).
Panel 1A: Definition of EQ distance
Space
Expected number of EQs with magnitude m
Background
Induced seismicity shows:
• Higher intensity of repeaters
• Higher background rate
• Higher spatial offspring separation
• Higher temporal offspring separation
Repeaters
Clustered events
Panel 1B: Bimodal distribution (theory)
We notice that   TR and log   log T  log R, where
rescaled time T   10
Magnitude m
 bm /2
,
rescaled distance R  r d 10  bm /2

r
4. Seismicity before and during geothermal production in Coso and Salton Sea
Coso geothermal

Time
(Fractal) dimension of epicenters
Clusters
   r 10
Intercurrence time
 bm
Spatial distance
,  0
Gutenberg-Richter law
[M. Baiesi and M. Paczuski, PRE, 69, 066106 (2004)]
Rescaled distance, log R
Before production
d
Time decay of offspring is slower in tectonic regions. The Omori parameter p is
changing from 2 in induced regions to 1.5 in mixed regions, to 1 in tectonic regions.
During production
Homogeneous flow
(no clusters)
Rescaled time, log T
Start of geothermal production
Salton Sea
[Zaliapin et al., PRL, 101, 018501 (2008)]
 The figure below shows the 2D distribution of the time and
space components of the nearest-neighbor earthquake
distance for southern California
 The bimodal structure is used to identify the cluster and
background populations
 This study explores in detail such 2D distributions for different
local regions and report significant differences that we claim to
be related to induced vs. tectonic origin of earthquakes
Background = weak links
(as in stationary, inhomogeneous
Poisson process)
Before production
Before production
Tectonic seismicity:
• Low background
• Larger clusters
• Weak repeaters
Proportion of background events as a function of time in Coso geothermal (dashed) and Coso non-geothermal (solid) areas. The proportion is
estimated in a 5-year moving window. The results are shown at the end of the window; hence the point at 1990 corresponds to the interval [19851990], etc. Notice the abrupt increase of background events in Coso geothermal area in 1989 that corresponds to the interval [1984-1989] and is
associated with the onset of geothermal production.
5. References and acknowledgements
1.
2.
3.
4.
During production
Clustered part = strong links (events
are much closer to each other than in
the background part)
During production
Mixed seismicity:
• High background
• Smaller clusters
• Active repeaters
5.
6.
7.
8.
Baiesi, M and M. Paczuski (2004) Scale-free networks of earthquakes and aftershocks. Phys. Rev. E, 69, 066106.
Brodsky, E. E., & Lajoie, L. J. (2013). Anthropogenic seismicity rates and operational parameters at the Salton Sea Geothermal Field. Science, 341(6145), 543546.
Hauksson, E. and W. Yang, and P.M. Shearer, (2012) Waveform Relocated Earthquake Catalog for Southern California (1981 to 2011). Bull. Seismol. Soc. Am.,
102(5), 2239-2244.
Waldhauser, F. and D.P. Schaff (2008), Large-scale relocation of two decades of Northern California seismicity using cross-correlation and double-difference
methods, J. Geophys. Res., 113, B08311, doi:10.1029/2007JB005479.
Zaliapin, I., A. Gabrielov, H. Wong, and V. Keilis-Borok (2008). Clustering analysis of seismicity and aftershock identification, Phys. Rev. Lett., 101.
Zaliapin, I. and Y. Ben-Zion (2011). Asymmetric distribution of early aftershocks on large faults in California, Geophys. J. Intl., 185, 1288-1304, doi:
10.1111/j.1365-246X.2011.04995.x.
Zaliapin, I. and Y. Ben-Zion (2013a) Earthquake clusters in southern California, I: Identification and stability. J. Geophys. Res., 118, 2847-2864.
Zaliapin, I. and Y. Ben-Zion (2013b) Earthquake clusters in southern California, II: Classification and relation to physical properties of the crust. J. Geophys. Res.,
118, 2865-2877.
We are grateful to Margaret Boettcher and
Integrated Seismic Systems International (ISSI )
for sharing with us the TauTona gold mine catalog.
The research is supported by the SCEC, project 15120
(the United States Geological Survey Grant G09AP00019
and the National Science Foundation grant DMS-0934871)