Pelatihan :

Techniques in Active Tectonic StudyJuni 20-Juli 2, 2013

Instruktur: Prof. J Ramon Arrowsmith (JRA)Dari Arizona State University (ASU) - US

Tempat Pelaksanaan: Ruang Pangea, Laboratorium Gempabumi (LabEarth) –

Puslit Geoteknologi LIPI dan Kuliah lapangan akan dilakukan disekitar Sesar Lembang, Jawa Barat.

* Lebih jelas baca TOR/KAK dan daftar acara

Earthquake RecurrenceOutline of this lecture

• Simple models of earthquake recurrence• Segmentation• Earthquake rate models: Gutenberg-Richter

and Characteristic• Earthquake recurrence simulation

Simple Earthquake Machine

Subduction earthquake cycle

A. Periodic earthquake model in which stress levels at the time of rupture and after it are known. These yield a predictable time and slip for each earthquake. B. Time-predictable model based on a consistent stress level at which failure occurs. Stress drop and slip magnitude are unpredictable, but given previous slip, time until the next earthquake (with unknown slip) is predictable. C. Slip-predictable model based on a consistent stress level at the end of an earthquake. Given time since the last rupture, magnitude of slip is predictable. Modified after Shimaki and Nakata (1980) Burbank and Anderson

Burbank and Anderson, 2011, Tectonic Geomorphology, Chapter 4

Burbank and Anderson, 2011, Tectonic Geomorphology, Chapter 4

Burbank and Anderson

Basic fault segmentation

Fault zone is comprised of heterogeneous non coplanar fault surfaces bounding oblate blocks whose geometry and activity varies in time and space

Map view mode II step

(bend)

Cross-section view

mode III step (bend)

3D mixed mode

stepover

Strong influences on •Stress and displacement fields around the fault surfaces•Further development and linkage•Fluid flow•Rupture dynamics•Fault zone strength

Questions:Geometric—Fault surface and block shapes and sizesTime—How long are they active? What is slip history? Block motion history?Development—Linkage and evolution of roughness

Predicting the endpoints of earthquake ruptures (I)

Wesnousky, 2006

Predicting the endpoints of earthquake ruptures (II)

Wesnousky, 2006

“stop light color scheme”

About 2/3 rupture terminations are associated with discontinuities or fault ends

Ste

p si

ze

Megathrust earthquake segmentation model for Indonesia region

(Irsyam et.al., 2010)

Estimated maximum magnitude and slip rate of faults in Indonesia

(Irsyam et.al, 2010)

Earthquake magnitude and frequency: Earthquake rate model

1984

“…individual faults and fault segments tend to generate essentially the same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum” given fault geometry

Full Rupture of seismogenic width of

fault

Zielke and Arrowsmith, 2008

High resolution satellite imagery based offset reconstruction along Fuyun Fault, China

Approximately 2kyr recurrence interval

Burbank and Anderson

If we know slip rate du/dt

And we assume u(x) per event

We can get recurrence time

uave or umax per event should also imply length and M

Synoptic view of continental shear zone (Scholz, 1988)

Burbank and Anderson, 2011, Tectonic Geomorphology, Chapter 4Modified from Zielke and Arrowsmith, 2008

Burbank and Anderson, 2011, Tectonic Geomorphology, Chapter 4Modified from Zielke and Arrowsmith, 2008

Thatcher, 1990

Zielke and Arrowsmith, 2008; Zielke, 2009

Quasi-static earthquake simulator using elastic dislocations with stress boundary conditions and simple friction produces synthetic earthquake catalogue (900,000 events > 5km2 over 540kyr; cumulative stress history)

So what do these earthquakes look like along the fault over time?

Bimodal Seismicity DistributionBimodal Seismicity DistributionDown-dip rupture width RW of small EQs is limited by

zp

Rupture of strength barrier zp causes activation of full seismic zone

Abrupt increase in RW and RA at transition from small to large EQs

Abrupt increase in Magnitude

Mag. vs. Freq.

RW vs. Freq.

Small vs. Large EQ

Moderate M, partial rupture, Gutenberg-Richter

Large M, full rupture, Characteristic

Zielke and Arrowsmith, 2008

Implies bimodal M, RA, and slip at surface->controlling influence of event on landscape