A brief history of seismology Early 1800’s – theoretical development of elastic wave propagation (Cauchy, Poisson, Stokes, Rayleigh, etc)– knew about body waves and surface waves long before observed 1857 Mallett, Naples – concept that earthquakes radiate seismic waves (though he assumed that all sources were explosions and only radiated P waves)

History -- continued First time-recording seismometer (Cecchi, 1875) Deployments of seismometers in Japan by Milne et al. in 1880’s First teleseism recorded in – first seismometer in US (at Lick observatory) 1898 – first damped seismometer (Wiechert) Early 1900’s electromagnetic sensing (Galitzin)

History--continued Recording earthquakes at various ranges led to velocity structure Oldham (1900) identifed P and S and surface waves Oldham (1906) identified the core shadow Mohorovicic (1909) identified crust-mantle boundary Travel time tables (Zoppritz 1907, Gutenberg, 1914 (radius of the core), JB

Raypaths for P and S demonstrating the core shadow

Example of travel time curves

History continued 1928 Wadati identifies existence of deep earthquakes – Wadati-Benioff zones (still not understood how deep earthquakes happen) Nuclear tests (1946 Bikini atoll, 1949 first Russian test) – later go underground – lots of bucks for seismology 1961 WWSSN 1960’s computers, ISC started in 1964 – vast improvement in location ability – see plate boundaries 1960 Chile eq (M=9.5) – free oscillations 1960—1980 Geophysical inverse theory developed largely to look at Earth structure – 1D structure including mantle discontinuities firmly established – beginning of IRIS – easy access to data 1990– seismic tomography, imaging the 3D structure

Shear velocity % isovelocity surfaces Includes S and SS cluster analysis data

Seismometers on the moon

Continuously excited oscillations of the sun observed by looking at doppler shift of spectral lines -- helioseismology

History -- continued Reid develops “elastic rebound theory” after 1906 earthquake 1923 Nakano develops double-couple model of the seismic source (controversial until the 60’s!) 1935 – development of Richter magnitude scale (better estimate of size is “moment” developed by Aki in 1966)

Image of slip surface outlines 1300-km- long earthquake, lasting for about 8 minutes This could be produced for future events within 20 to 30 minutes of the earthquake start time