Dr. Marachi started his professional career by working for Converse Davis & Associates in Pasadena, California in May of 1969 as a project engineer. He was assigned to work on the Castaic Power Plant project. His work included:

• All rock and soil stability evaluations
• All instrumentation planning and installations
• Design of various sections of the project, e.g. penstocks, manifold structure
• Design (in cooperation with Mr. Chuck Stewart) of the 180 ft. high pump-storage afterbay dam (presently named Elderberry Dam), including:
  • Seepage analysis for normal operations
  • Seepage analysis and design of the upstream section configuration for rapid drawdown (52 ft in 65 hrs). This is an extremely high requirement for a dam.
  • Dynamic finite element analysis allowing for pore pressure generation and dissipation to assess liquefaction potential. This was one of the first such studies done in practice.
    

For another project, evaluation of seepage through the proposed soil embankment reservoir for the City of Industry, Dr. Marachi was the first to utilize the first available version of the finite-element transient seepage computer program, then being developed by Professors Paul Witherspoon and Shlom Newman (then a Ph.D. candidate).

The 9 Feb. 1971 San Fernando earthquake gave him the impetus to perform a number of highly critical and challenging assignments, such as:

• Detail investigation of liquefaction at Joseph Jensen Filtration Plant and Holt boys camp,
• Dynamic soil amplification study in San Fernando Valley/ portions of a contract for NSF through Professor H.B. Seed,
• Development of the methodology and performance of a large number of site amplification studies using Fourier analysis of the random site motions.

Dr. Marachi successfully applied this method to Holy Cross Hospital which was severely damaged. Subsequently, he applied this method to assess the site amplification at many critical installations, e.g. Goleta and Ellwood power plants, Hyperion treatment plant (expansion), Supermex LNG facility, and many of the critical buildings at the Jet Propulsion Laboratory. He has since used this method to measure the first few natural frequencies of arch dams and intake/outlet towers to validate/calibrate the computer finite element models of such structures prior to performing exhaustive computational efforts.

In this period Dr. Marachi also developed a method for calculating the statistical probabilities associated with different levels of ground shaking at a given site based on past recorded seismic events within a specified distance from the site. He published it in the International Conference of Seismic Microzonation in 1971. He and some of his colleagues, e.g. David Leads of Dames & Moore, used this method to assess seismic risk for many of the high rise buildings presently in Los Angeles downtown. He also used this method to develop seismic criteria for all buildings in the Jet Propulsion Laboratory in Pasadena, CA. This method was important as it was one of the first methods to use ‘probability’ to arrive at selecting seismic design criteria. (Later in, 1976, Professors Shah and Karamidjian of Stanford University developed a probability method based on fault activity, and this was later improved by Dr. Norman Abrahamson and is presently being used to develop planning criteria for most important projects, e.g. the new section of the San Francisco/Oakland Bay Bridge.)

Dr. Marachi was also very active in various engineering professional societies. He became a member of the SEAOSC committee to rewrite the seismic design section of the Uniform Building Code. He also directed a 12-hr workshop for ASCE members and taught seismicity, faulting, ground motion, liquefaction, wave propagation, and dynamic response to the practicing engineers. He also chaired an ASCE committee for developing practice standards for verification and dissemination of computer programs. He was one of the first few to become a member of EERI (Earthquake Engineering Research Institute) when such memberships were by invitation only.

On the side, he also taught a four unit undergraduate course in soil mechanics and foundation engineering at the Cal State University, Los Angeles in 1972.